Patent Publication Number: US-10316774-B2

Title: System for method for controlling engine knock of a variable displacement engine

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     The present application claims priority to U.S. Provisional Patent Application Ser. No. 62/347,894, filed on Jun. 9, 2016. The entire contents of the above-referenced application are hereby incorporated by reference in its entirety for all purposes. 
    
    
     FIELD 
     The present description relates to systems and methods for controlling engine knock of an engine. The systems and methods may be applied to engines that may deactivate selected engine cylinders via poppet valves. 
     BACKGROUND AND SUMMARY 
     An engine may include one or more knock sensors to sense engine knock. In a petrol engine, knock occurs in an engine after an air-fuel mixture in the cylinder is ignited by a spark. In particular, the air-fuel mixture is ignited at a location in the cylinder outside of a flame front in the cylinder created by the spark. The second ignition after the spark ignition is produced by rising pressure in the cylinder and it causes a pressure oscillation in the cylinder that produces a ping or knocking sound in the engine. The engine block may include several cylinders and support structures that may improve or degrade the capacity of the engine knock sensors to detect engine knock. Consequently, two or more knock sensors may be deployed in an engine to detect engine knock. However, it may be difficult to detect engine knock with even two engine knock sensors since combustion noise and vibration of the engine block may mask engine knock that is detectable via the engine knock sensors. 
     The inventor herein has recognized the above-mentioned disadvantages and has developed a method for operating an engine, comprising: operating the engine with a first group of combusting cylinders in response to a first condition; operating the engine with a second group of combusting cylinders in response to a second condition; adjusting spark timing of a cylinder in response to an indication of knock via a first group of sensors during the first condition; and adjusting spark timing of the cylinder in response to an indication of knock via a second group of sensors during the second condition. 
     By adjusting spark timing in response to different groups of knock sensors during different engine operating conditions, it may be possible to provide the technical result of improved engine knock detection. For example, if all engine cylinders are active and combusting air and fuel, it may be desirable to assess the presence or absence of engine knock via two engine knock sensors. However, if one or more cylinders is deactivated and not combusting air and fuel, it may be desirable to assess the presence or absence of engine knock via a single sensor and ignore output of a second sensor. Deactivating one or more engine cylinders may reduce combustion noise and improve a signal to noise ratio of a knock sensor. 
     The present description may provide several advantages. In particular, the approach may improve engine knock sensing. Additionally, the approach may reduce the possibility of engine degradation. Further, the approach may improve engine knock sensing when cylinders of an engine are deactivated in different ways. 
     The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings. 
     It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The advantages described herein will be more fully understood by reading an example of an embodiment, referred to herein as the Detailed Description, when taken alone or with reference to the drawings, where: 
         FIG. 1A  is a schematic diagram of a single cylinder of an engine; 
         FIG. 1B  is a schematic diagram of the engine of  FIG. 1A  included in a powertrain; 
         FIGS. 2A-2F  show example valve configurations for four cylinder engines with cylinders that may be deactivated; 
         FIGS. 3A and 3B  show example patterns of activated and deactivated cylinders of a four cylinder engine; 
         FIGS. 4A-4C  show example valve configurations for eight cylinder engine with cylinders that may be deactivated; 
         FIG. 5A  shows example camshafts for a hydraulically operated valve deactivating system; 
         FIG. 5B  shows example deactivating valve operators for the hydraulically operated valve deactivating system shown in  FIG. 5A ; 
         FIG. 5C  shows an example valve operator for the hydraulically operated valve deactivating system shown in  FIG. 5A ; 
         FIG. 5D  shows an example cylinder and valve deactivation sequence for the hydraulically operated valve deactivating system shown in  FIG. 5A ; 
         FIG. 6A  shows an example camshaft for an alternative hydraulically operated valve deactivating system; 
         FIG. 6B  shows a cross section of a camshaft and saddle for the hydraulically operated valve deactivating system shown in  FIG. 6A ; 
         FIG. 6C  shows example valve deactivating valve operators for the hydraulically operated valve deactivating system shown in  FIG. 6A ; 
         FIG. 6D  is an example cylinder and valve deactivation sequence for the hydraulically operated valve deactivating system shown in  FIG. 6A ; 
         FIG. 7  is a flowchart of an example method for operating an engine with deactivating cylinders and valves; 
         FIG. 8A  is a flowchart of an example method for selectively activating and deactivating cylinders and cylinder valves of an engine with both deactivating and non-deactivating intake valves and only non-deactivating exhaust valves; 
         FIG. 8B  is a block diagram for estimating an amount of oil in a deactivated cylinder; 
         FIG. 9  is an example sequence for activating and deactivating cylinders and cylinder valves of an engine having both deactivating and non-deactivating intake valves and only non-deactivating exhaust valves; 
         FIG. 10  is a flowchart of an example method for selectively activating and deactivating cylinders and cylinder valves of an engine with both deactivating and non-deactivating intake valves and non-deactivating and deactivating exhaust valves; 
         FIG. 11  is a flowchart of a method for determining available cylinder modes; 
         FIG. 12  is a flowchart of a method for evaluating whether or not cylinder deactivation may be performed responsive to cylinder activation/deactivation busyness; 
         FIG. 13  is a sequence showing cylinder activation and deactivation according to the method of  FIG. 12 ; 
         FIG. 14  is a flowchart of a method for evaluating engine fuel consumption as a basis for selectively allowing cylinder deactivation; 
         FIG. 15  is a flowchart of a method for evaluating engine fuel consumption as a basis for selectively allowing cylinder deactivation; 
         FIG. 16  is a flowchart of a method for evaluating engine cam phasing for selecting engine cylinder modes; 
         FIG. 17  is a sequence showing selecting engine cylinder modes responsive to engine cam phasing; 
         FIG. 18  is a flowchart of a method for selecting engine cylinder mode responsive to engine fuel consumption based on operating an engine in various transmission gears; 
         FIG. 19  is a sequence showing selecting transmission gears and an actual total number of active cylinders to improve engine fuel consumption; 
         FIG. 20  is a flowchart of a method for selecting different engine cylinder modes in while operating a vehicle in various deceleration modes; 
         FIG. 21  is a sequence for operating an engine in different cylinder modes based on operating a vehicle in different deceleration modes; 
         FIG. 22  is a flowchart for determining if conditions are present for operating an engine in various variable displacement (VDE) engine modes; 
         FIG. 23  is a flowchart of a method for controlling engine intake manifold pressure; 
         FIG. 24  is a sequence showing engine intake manifold pressure control according to the method of  FIG. 23 ; 
         FIG. 25  is a flowchart of a method for controlling engine intake manifold pressure; 
         FIG. 26  is an operating sequence for controlling engine intake manifold pressure; 
         FIGS. 27A and 27B  show a flowchart for adjusting engine actuators to improve engine cylinder mode changes; 
         FIGS. 28A and 28B  show sequences for improving cylinder mode changes; 
         FIG. 29  is a flowchart for delivering fuel to an engine during cylinder mode changes; 
         FIG. 30  is a sequence for showing fuel delivery to an engine during cylinder mode changes; 
         FIG. 31  is a flowchart of a method for controlling engine oil pressure during cylinder mode changes; 
         FIG. 32  is a sequence showing oil pressure control during cylinder mode changes; 
         FIG. 33  is a flowchart of a method to improve engine knock control during cylinder mode changes; 
         FIG. 34  is a sequence showing engine knock control during different engine cylinder modes; 
         FIG. 35  is a flowchart of a method for adjusting spark gain; 
         FIG. 36  is a sequence showing adjustable spark gain; 
         FIG. 37  is a flowchart of a method for determining a knock reference value depending on cylinder mode; 
         FIG. 38  is a sequence showing selection of a knock reference value; 
         FIG. 39  is a flowchart of a method for selecting engine cylinder modes in the presence of valve degradation; 
         FIG. 40  is a flowchart of a sequence for selecting engine cylinder modes in the presence of valve degradation; 
         FIG. 41  is a flowchart for sampling an oxygen sensor responsive to cylinder deactivation; and 
         FIG. 42  is a flowchart for sampling a camshaft sensor responsive to cylinder deactivation. 
     
    
    
     DETAILED DESCRIPTION 
     The present description is related to systems and methods for selectively activating and deactivating cylinders and cylinder valves of an internal combustion engine. The engine may be configured and operate as is shown in  FIGS. 1A-6D . Various methods and prophetic operating sequences for an engine that includes deactivating valves are shown in  FIGS. 7-42 . The different methods may operate cooperatively and with the systems shown in  FIGS. 1A-6D . 
     Referring to  FIG. 1A , internal combustion engine  10 , comprising a plurality of cylinders, one cylinder of which is shown in  FIG. 1A , is controlled by electronic engine controller  12 . Engine  10  is comprised of cylinder head casting  35  and block  33 , which include combustion chamber  30  and cylinder walls  32 . Piston  36  is positioned therein and reciprocates via a connection to crankshaft  40 . Flywheel  97  and ring gear  99  are coupled to crankshaft  40 . Starter  96  (e.g., low voltage (operated with less than 30 volts) electric machine) includes pinion shaft  98  and pinion gear  95 . Pinion shaft  98  may selectively advance pinion gear  95  to engage ring gear  99 . Starter  96  may be directly mounted to the front of the engine or the rear of the engine. In some examples, starter  96  may selectively supply torque to crankshaft  40  via a belt or chain. In one example, starter  96  is in a base state when not engaged to the engine crankshaft. 
     Combustion chamber  30  is shown communicating with intake manifold  44  and exhaust manifold  48  via respective intake valve  52  and exhaust valve  54 . Each intake and exhaust valve may be operated by an intake camshaft  51  and an exhaust camshaft  53 . The position of intake camshaft  51  may be determined by intake cam sensor  55 . The position of exhaust camshaft  53  may be determined by exhaust cam sensor  57 . An angular position of intake valve  52  may be moved relative to crankshaft  40  via phasing adjusting device  59 . An angular position of exhaust valve  54  may be moved relative to crankshaft  40  via phasing adjusting device  58 . Valve operators shown in detail below may transfer mechanical energy from intake camshaft  51  to intake valve  52  and from exhaust camshaft  53  to exhaust valve  54 . Further, in other examples, a single camshaft may operate intake valve  52  and exhaust valve  54 . 
     Fuel injector  66  is shown positioned to inject fuel directly into cylinder  30 , which is known to those skilled in the art as direct injection. Optional fuel injector  67  is shown positioned to port inject fuel to cylinder  30 , which is known to those skilled in the art as port fuel injection. Fuel injectors  66  and  67  deliver liquid fuel in proportion to pulse widths from controller  12 . Fuel is delivered to fuel injectors  66  and  67  by a fuel system (not shown) including a fuel tank, fuel pump, and fuel rail (not shown). In one example, a high pressure, dual stage, fuel system may be used to generate higher fuel pressures. 
     In addition, intake manifold  44  is shown communicating with turbocharger compressor  162  and engine air intake  42 . In other examples, compressor  162  may be a supercharger compressor. Shaft  161  mechanically couples turbocharger turbine  164  to turbocharger compressor  162 . Optional electronic throttle or central throttle  62  adjusts a position of throttle plate  64  to control air flow from compressor  162  to intake manifold  44 . Pressure in boost chamber  45  may be referred to a throttle inlet pressure since the inlet of throttle  62  is within boost chamber  45 . The throttle outlet is in intake manifold  44 . In some examples, a charge motion control valve  63  is positioned downstream of throttle  62  and upstream of intake valve  52  in a direction of air flow into engine  10  and operated by controller  12  to regulate air flow into combustion chamber  30 . Compressor recirculation valve  47  may be selectively adjusted to a plurality of positions between fully open and fully closed. Waste gate  163  may be adjusted via controller  12  to allow exhaust gases to selectively bypass turbine  164  to control the speed of compressor  162 . Air filter  43  cleans air entering engine air intake  42 . 
     Distributorless ignition system  88  provides an ignition spark to combustion chamber  30  via spark plug  92  in response to controller  12 . Universal Exhaust Gas Oxygen (UEGO) sensor  126  is shown coupled to exhaust manifold  48  upstream of catalytic converter  70 . Alternatively, a two-state exhaust gas oxygen sensor may be substituted for UEGO sensor  126 . Pressure sensor  127  is shown positioned in exhaust manifold  48  as an exhaust pressure sensor. Alternatively, pressure sensor  127  may be position in combustion chamber  30  as a cylinder pressure sensor. Spark plug  92  may also serve as an ion sensor for ignition system  88 . 
     Converter  70  can include multiple catalyst bricks, in one example. In another example, multiple emission control devices, each with multiple bricks, can be used. Converter  70  can be a three-way type catalyst in one example. Further, converter  70  may include a particulate filter. 
     Controller  12  is shown in  FIG. 1A  as a conventional microcomputer including: microprocessor unit  102 , input/output ports  104 , read-only memory  106  (e.g., non-transitory memory), random access memory  108 , keep alive memory  110 , and a conventional data bus. Controller  12  is shown receiving various signals from sensors coupled to engine  10 , in addition to those signals previously discussed, including: engine coolant temperature (ECT) from temperature sensor  112  coupled to cooling sleeve  114 ; engine mount with integrated vibration and/or movement sensors  117  which may provide feedback to compensate and evaluate engine noise, vibration, and harshness; a position sensor  134  coupled to an accelerator pedal  130  for sensing force applied by foot  132 ; a position sensor  154  coupled to brake pedal  150  for sensing force applied by foot  152 , a measurement of engine manifold pressure (MAP) from pressure sensor  122  coupled to intake manifold  44 ; an engine position sensor from a Hall effect sensor  118  sensing crankshaft  40  position; a measurement of air mass entering the engine from sensor  120 ; and a measurement of throttle position from sensor  68 . Barometric pressure may also be sensed (sensor not shown) for processing by controller  12 . In a preferred aspect of the present description, engine position sensor  118  produces a predetermined number of equally spaced pulses every revolution of the crankshaft from which engine speed (RPM) can be determined. Controller  12  may also receive information from other sensors  24  which may include but are not limited to engine oil pressure sensors, ambient pressure sensors, and engine oil temperature sensors. 
     During operation, each cylinder within engine  10  typically undergoes a four stroke cycle: the cycle includes the intake stroke, compression stroke, expansion stroke, and exhaust stroke. A cylinder cycle for a four stroke engine is two engine revolutions and an engine cycle is also two revolutions. During the intake stroke, generally, the exhaust valve  54  closes and intake valve  52  opens. Air is introduced into combustion chamber  30  via intake manifold  44 , and piston  36  moves to the bottom of the cylinder so as to increase the volume within combustion chamber  30 . The position at which piston  36  is near the bottom of the cylinder and at the end of its stroke (e.g. when combustion chamber  30  is at its largest volume) is typically referred to by those of skill in the art as bottom dead center (BDC). 
     During the compression stroke, intake valve  52  and exhaust valve  54  are closed. Piston  36  moves toward the cylinder head casting  35  so as to compress the air within combustion chamber  30 . The point at which piston  36  is at the end of its stroke and closest to the cylinder head casting  35  (e.g. when combustion chamber  30  is at its smallest volume) is typically referred to by those of skill in the art as top dead center (TDC). In a process hereinafter referred to as injection, fuel is introduced into the combustion chamber. In a process hereinafter referred to as ignition, the injected fuel is ignited by known ignition means such as spark plug  92 , resulting in combustion. 
     During the expansion stroke, the expanding gases push piston  36  back to BDC. Crankshaft  40  converts piston movement into a rotational torque of the rotary shaft. Finally, during the exhaust stroke, the exhaust valve  54  opens to release the combusted air-fuel mixture to exhaust manifold  48  and the piston returns to TDC. Note that the above is shown merely as an example, and that intake and exhaust valve opening and/or closing timings may vary, such as to provide positive or negative valve overlap, late intake valve closing, or various other examples. 
     Driver demand torque may be determined via a position of accelerator pedal  130  and vehicle speed. For example, accelerator pedal position and vehicle speed may index a table that outputs a driver demand torque. The driver demand torque may represent a desired engine torque or torque at a location along a driveline that includes the engine. Engine torque may be determined from driver demand torque via adjusting the driver demand torque for gear ratios, axle ratios, and other driveline components. 
     Referring now to  FIG. 1B ,  FIG. 1B  is a block diagram of a vehicle  125  including a driveline  100 . The driveline of  FIG. 1B  includes engine  10  shown in  FIG. 1A . Driveline  100  may be powered by engine  10 . Engine torque may be adjusted via engine torque actuator  191 , which may be a fuel injector, camshaft, throttle, or other device. Engine crankshaft  40  is shown coupled to torque converter  156 . In particular, engine crankshaft  40  is mechanically coupled to torque converter impeller  285 . Torque sensor  41  provides torque feedback and it may be used to evaluate engine noise, vibration, and harshness. Torque converter  156  also includes a turbine  186  to output torque to transmission input shaft  170 . Transmission input shaft  170  mechanically couples torque converter  156  to automatic transmission  158 . Torque converter  156  also includes a torque converter bypass lock-up clutch  121  (TCC). Torque is directly transferred from impeller  185  to turbine  186  when TCC is locked. TCC is electrically operated by controller  12 . Alternatively, TCC may be hydraulically locked. In one example, the torque converter may be referred to as a component of the transmission. 
     When torque converter lock-up clutch  121  is fully disengaged, torque converter  156  transmits engine torque to automatic transmission  158  via fluid transfer between the torque converter turbine  186  and torque converter impeller  185 , thereby enabling torque multiplication. In contrast, when torque converter lock-up clutch  121  is fully engaged, the engine output torque is directly transferred via the torque converter clutch to an input shaft  170  of transmission  158 . Alternatively, the torque converter lock-up clutch  121  may be partially engaged, thereby enabling the amount of torque directly relayed to the transmission to be adjusted. The controller  12  may be configured to adjust the amount of torque transmitted by torque converter  121  by adjusting the torque converter lock-up clutch in response to various engine operating conditions, or based on a driver-based engine operation request. 
     Automatic transmission  158  includes gears (e.g., reverse and gears  1 - 6 )  136  and forward clutches  135  for the gears. The gears  136  (e.g.,  1 - 10 ) and clutches  135  may be selectively engaged to propel a vehicle. Torque output from the automatic transmission  158  may in turn be relayed to wheels  116  to propel the vehicle via output shaft  160 . Specifically, automatic transmission  158  may transfer an input driving torque at the input shaft  170  responsive to a vehicle traveling condition before transmitting an output driving torque to the wheels  116 . 
     Further, a frictional force may be applied to wheels  116  by engaging wheel brakes  119 . In one example, wheel brakes  119  may be engaged in response to the driver pressing his foot on a brake pedal as shown in  FIG. 1A . In other examples, controller  12  or a controller linked to controller  12  may apply engage wheel brakes. In the same way, a frictional force may be reduced to wheels  116  by disengaging wheel brakes  119  in response to the driver releasing his foot from a brake pedal. Further, vehicle brakes may apply a frictional force to wheels  116  via controller  12  as part of an automated engine stopping procedure. 
     Controller  12  may be configured to receive inputs from engine  10 , as shown in more detail in  FIG. 1A , and accordingly control a torque output of the engine and/or operation of the torque converter, transmission, clutches, and/or brakes. As one example, an engine torque output may be controlled by adjusting a combination of spark timing, fuel pulse width, fuel pulse timing, and/or air charge, by controlling throttle opening and/or valve timing, valve lift and boost for turbo- or super-charged engines. In the case of a diesel engine, controller  12  may control the engine torque output by controlling a combination of fuel pulse width, fuel pulse timing, and air charge. In all cases, engine control may be performed on a cylinder-by-cylinder basis to control the engine torque output. Controller  12  may also control torque output and electrical energy production from DISG by adjusting current flowing to and from field and/or armature windings of DISG as is known in the art. 
     When idle-stop conditions are satisfied, controller  12  may initiate engine shutdown by shutting off fuel and/or spark to the engine. However, the engine may continue to rotate in some examples. Further, to maintain an amount of torsion in the transmission, the controller  12  may ground rotating elements of transmission  158  to a case  159  of the transmission and thereby to the frame of the vehicle. When engine restart conditions are satisfied, and/or a vehicle operator wants to launch the vehicle, controller  12  may reactivate engine  10  by craning engine  10  and resuming cylinder combustion. 
     Intake manifold  44  of engine  10  is in pneumatic communication with vacuum reservoir  177  via valve  176 . Vacuum reservoir may provide vacuum to brake booster  178 , heating/ventilation/cooling system  179 , waste gate actuator  180 , and other vacuum operated systems. In one example, valve  176  may be a solenoid valve that may be opened and closed to selectively allow or prevent communication between intake manifold  44  and vacuum consumers  178 - 180 . Additionally, a vacuum source  183 , such as a pump or ejector, may selectively provide vacuum to engine intake manifold  44  so that if there is leakage through the throttle  62 , engine  10  may be restarted with the engine intake manifold pressure being less than atmospheric pressure. Vacuum source  183  may also selectively supply vacuum to vacuum consumers  178 - 180  via three way valve  171 , for example when vacuum level in vacuum reservoir  177  is less than a threshold. The volume of intake manifold  44  may be adjusted via variable plenum volume valve  175 . 
     Referring now to  FIG. 2A , an example engine configuration of engine  10  is shown. In this configuration, engine  10  is an inline four cylinder engine with a first valve configuration. Portions of the engine&#39;s combustion chambers formed in cylinder head casting  35 , which also may be referred to as part of a cylinder, are numbered from  1 - 4  according to cylinder numbers  1 - 4  as indicated for each engine cylinder  200 . In this example, each combustion chamber is shown with two intake valves and two exhaust valves. Deactivating intake valves  208  are shown as poppet valves with an X through the poppet valve shaft. Deactivating exhaust valves  204  are shown as poppet valves with an X through the poppet valve shaft. Non-deactivating intake valves  206  are shown as poppet valves. Non-deactivating exhaust valves  202  are also shown as poppet valves. 
     Camshaft  270  is shown in mechanical communication with non-deactivating exhaust valves  202  via non-deactivating exhaust valve operators  250 . Camshaft  270  is also in mechanical communication with non-deactivating intake valves  206  via non-deactivating intake valve operators  251 . Camshaft  270  is shown in mechanical communication with deactivating exhaust valves  204  via deactivating exhaust valve operators  252 . Camshaft  270  is also in mechanical communication with deactivating intake valves  208  via deactivating intake valve operators  253 . Some intake and exhaust valves are not shown with valve operators to reduce busyness in the figure, but each valve is accompanied by a valve operator (e.g., non-deactivating valves are accompanied with non-deactivating valve operators and deactivating valves are accompanied with deactivating valve operators). 
     In this configuration, cylinders  2  and  3  are shown with deactivating intake valves  208  and deactivating exhaust valves  204 . Cylinders  1  and  4  are shown with non-deactivating intake valves  206  and non-deactivating exhaust valves  202 . However, in some examples, non-deactivating intake valves  206  and non-deactivating exhaust valves  202  may be replaced with deactivating exhaust valves and deactivating intake valves so that all engine cylinders may be selectively deactivated. 
     The configuration of  FIG. 2A  provides for deactivating cylinders  2  and  3  together or separately. Further, since both intake and exhaust valves of cylinders  2  and  3  are deactivating, these cylinders are deactivated by closing both intake and exhaust valves for an entire engine cycle and ceasing fuel flow to cylinders  2  and  3 . For example, if the engine has a firing order of 1-3-4-2, the engine may fire in an order of 1-2-1-2, or 1-3-2-1-4-2, or 1-3-2-1-3-2-1-4-2, or other combinations where cylinders  1  and  2  combust air and fuel. However, if cylinders  1 - 4  each included deactivating intake and exhaust valves, cylinders  1  and  2  may not fire (e.g., combust air and fuel) during some engine cycles. For example, the engine firing order may be 3-4-3-4, or 1-3-2-1-3-2, or 3-4-2-3-4-2, or other combinations where cylinders  1  and  2  do not combust air and fuel during an engine cycle. It should be noted that a deactivated cylinder may trap exhaust gases or fresh air depending on whether or not fuel is injected into the cylinder and combusted before the exhaust valves are deactivated in a closed position. 
       FIG. 2A  also slows a first knock sensor  203  and a second knock sensor  205 . First knock sensor  203  is positioned closer to cylinders  1  and  2 . Second knock sensor  205  is positioned closer to cylinders  3  and  4 . First knock sensor may be used to detect knock from cylinders  1  and  2  during some conditions and knock from cylinders  1 - 4  during other conditions. Likewise, second knock sensor  205  may be used to detect knock from cylinders  3  and  4  during some conditions and knock from cylinders  1 - 4  during other conditions. Alternatively, the knock sensors may be mechanically coupled to the engine block. 
     Referring now to  FIG. 2B , an alternative example engine configuration of engine  10  is shown. In this configuration, engine  10  is an inline four cylinder engine with a fraction of cylinders having only deactivating intake valves. Portions of the engine&#39;s combustion chambers formed in cylinder head casting  35  are again numbered from  1 - 4  as indicated for engine cylinders  200 . Each cylinder is shown with two intake valves and two exhaust valves. Cylinders  1 - 4  include non-deactivating exhaust valves  202  and no non-deactivating exhaust valves. Cylinders  1  and  4  also include non-deactivating intake valves  206  and no deactivating intake valves. Cylinders  2  and  3  include deactivating intake valves  208  and no non-deactivating intake valves. 
     Camshaft  270  is shown in mechanical communication with non-deactivating exhaust valves  202  via non-deactivating exhaust valve operators  250 . Camshaft  270  is also in mechanical communication with non-deactivating intake valves  206  via non-deactivating intake valve operators  251 . Camshaft  270  is also in mechanical communication with deactivating intake valves  208  deactivating intake valve operators  253 . Some intake and exhaust valves are not shown with valve operators to reduce busyness in the figure, but each valve is accompanied by a valve operator (e.g., non-deactivating valves are accompanied with non-deactivating valve operators and deactivating valves are accompanied with deactivating valve operators). 
     The configuration of  FIG. 2B  provides for deactivating cylinders  2  and  3  together or separately via deactivating intake valves  208 . The exhaust valves of cylinders  2  and  3  continue to open and close during an engine cycle as the engine rotates. Further, since only intake valves of cylinders  2  and  3  deactivate, these cylinders are deactivated by closing only intake valves for an entire engine cycle and ceasing fuel flow to cylinders  2  and  3 . Once again, if the engine has a firing order of 1-3-4-2, the engine may fire in an order of 1-2-1-2, or 1-3-2-1-4-2, or 1-3-2-1-3-2-1-4-2, or other combinations where cylinders  1  and  2  combust air and fuel. It should be noted that a deactivated cylinder in this configuration pulls exhaust into itself and expels exhaust during the deactivated cylinder&#39;s exhaust stroke. Specifically, exhaust is drawn into the deactivated cylinder when the deactivated cylinder&#39;s exhaust valve opens near the beginning of the exhaust stroke, and exhaust is expelled from the deactivated cylinder when the cylinder&#39;s piston approaches top-dead-center exhaust stroke before the exhaust valve closes. 
     In other examples, cylinders  1  and  4  may include the deactivating intake valves while cylinders  2  and  3  include non-deactivating intake valves. Otherwise, the valve arrangement may be the same. 
     Referring now to  FIG. 2C , another alternative example engine configuration of engine  10  is shown. In this configuration, engine  10  is an inline four cylinder engine and all engine cylinders include deactivating intake valves  208 , and none of the cylinders include deactivating exhaust valves. Portions of the engine&#39;s combustion chambers formed in cylinder head casting  35  are again numbered from  1 - 4  as indicated for engine cylinders  200 . Each cylinder is shown with two intake valves and two exhaust valves. Cylinders  1 - 4  include deactivating intake valves  208  and no deactivating intake valves. Cylinders  1 - 4  also include non-deactivating exhaust valves  202  and no deactivating exhaust valves. Engine  10  is also shown with first knock sensor  220  and second knock sensor  221 . 
     Camshaft  270  is shown in mechanical communication with non-deactivating exhaust valves  202  via non-deactivating exhaust valve operators  250 . Camshaft  270  is also in mechanical communication with deactivating intake valves  208  deactivating intake valve operators  253 . Some intake and exhaust valves are not shown with valve operators to reduce busyness in the figure, but each valve is accompanied by a valve operator (e.g., non-deactivating valves are accompanied with non-deactivating valve operators and deactivating valves are accompanied with deactivating valve operators). 
     The configuration of  FIG. 2C  provides for deactivating cylinders  1 - 4  in any combination during an engine cycle via deactivating only intake valves of cylinders  1 - 4 . The exhaust valves of cylinders  1 - 4  continue to open and close during an engine cycle as the engine rotates. Further, cylinders  1 - 4  may be deactivated by closing only intake valves for an entire engine cycle and ceasing fuel flow to cylinders  1 - 4 , or combinations thereof. If the engine has a firing order of 1-3-4-2, the engine may fire in an order of 1-2-1-2, or 1-3-2-1-4-2, or 1-3-2-1-3-2-1-4-2, or other combinations of cylinders  1 - 4  since each cylinder may be deactivated individually without deactivating other engine cylinders. It should be noted that a deactivated cylinder in this configuration pulls exhaust into itself and expels exhaust during the deactivated cylinder&#39;s exhaust stroke. Specifically, exhaust is drawn into the deactivated cylinder when the deactivated cylinder&#39;s exhaust valve opens near the beginning of the exhaust stroke, and exhaust is expelled from the deactivated cylinder when the cylinder&#39;s piston approaches top-dead-center exhaust stroke before the exhaust valve closes. 
     Referring now to  FIG. 2D , another alternative engine configuration of engine  10  is shown. The system of  FIG. 2D  is identical to the system of  FIG. 2A , except the system of  FIG. 2D  includes an intake camshaft  271  and an exhaust camshaft  272 . Portions of the engine&#39;s combustion chambers formed in cylinder head casting  35 , which also may be referred to as part of a cylinder, are numbered from  1 - 4  according to cylinder numbers  1 - 4  as indicated for each engine cylinder  200 . 
     Camshaft  271  is shown in mechanical communication with non-deactivating exhaust valves  202  via non-deactivating exhaust valve operators  250 . Camshaft  272  is in mechanical communication with non-deactivating intake valves  206  via non-deactivating intake valve operators  251 . Camshaft  271  is shown in mechanical communication with deactivating exhaust valves  204  via deactivating intake valve operators  252 . Camshaft  272  is in mechanical communication with deactivating intake valves  208  via deactivating intake valve operators  253 . Some intake and exhaust valves are not shown with valve operators to reduce busyness in the figure, but each valve is accompanied by a valve operator (e.g., non-deactivating valves are accompanied with non-deactivating valve operators and deactivating valves are accompanied with deactivating valve operators). 
     Referring now to  FIG. 2E , another alternative engine configuration of engine  10  is shown. The system of  FIG. 2E  is identical to the system of  FIG. 2B , except the system of  FIG. 2E  includes an intake camshaft  271  and an exhaust camshaft  272 . Portions of the engine&#39;s combustion chambers formed in cylinder head casting  35 , which also may be referred to as part of a cylinder, are numbered from  1 - 4  according to cylinder numbers  1 - 4  as indicated for each engine cylinder  200 . 
     Camshaft  271  is shown in mechanical communication with non-deactivating exhaust valves  202  via non-deactivating exhaust valve operators  250 . Camshaft  272  is in mechanical communication with non-deactivating intake valves  206  via non-deactivating intake valve operators  251 . Camshaft  272  is also in mechanical communication with deactivating intake valves  208  deactivating intake valve operators  253 . Some intake and exhaust valves are not shown with valve operators to reduce busyness in the figure, but each valve is accompanied by a valve operator (e.g., non-deactivating valves are accompanied with non-deactivating valve operators and deactivating valves are accompanied with deactivating valve operators). 
     Referring now to  FIG. 2F , another alternative engine configuration of engine  10  is shown. The system of  FIG. 2F  is identical to the system of  FIG. 2C , except the system of  FIG. 2F  includes an intake camshaft  271  and an exhaust camshaft  272 . Portions of the engine&#39;s combustion chambers formed in cylinder head casting  35 , which also may be referred to as part of a cylinder, are numbered from  1 - 4  according to cylinder numbers  1 - 4  as indicated for each engine cylinder  200 . 
     Camshaft  271  is shown in mechanical communication with non-deactivating exhaust valves  202  via non-deactivating exhaust valve operators  250 . Camshaft  272  is in mechanical communication with deactivating intake valves  208  deactivating intake valve operators  253 . Some intake and exhaust valves are not shown with valve operators to reduce busyness in the figure, but each valve is accompanied by a valve operator (e.g., non-deactivating valves are accompanied with non-deactivating valve operators and deactivating valves are accompanied with deactivating valve operators). 
     The deactivating valve operators shown in  FIGS. 2A-2F  may be a lever type (e.g., see  FIG. 6B ), a sleeve type (e.g., see U.S. Patent Publication No. 2014/0303873, U.S. patent application Ser. No. 14/105,000, entitled “Position Detection For Lobe Switching Camshaft System,” filed Dec. 12, 2013 and hereby fully incorporated by reference for all purposes), a cam lobe type, or a lash adjuster type. Further, each of the cylinder heads shown in  FIGS. 2A-2F  may be mechanically coupled to a same block  33  shown in  FIG. 1A . The cylinder heads shown in  FIGS. 2A-2F  may be formed from a same casting and the deactivating and non-deactivating valve operators for each cylinder head configuration may be varied as shown in  FIGS. 2A-2F . 
     Referring now to  FIG. 3A , an example cylinder deactivation pattern is shown. In  FIG. 3A , cylinder  4  of engine  10  is shown with an X through it to indicate that cylinder  4  may be deactivated during an engine cycle while cylinders  1 ,  2 , and  3  remain active. Active cylinders are shown without Xs to indicate the cylinders are active. One cylinder may be deactivated during an engine cycle via the system shown in  FIG. 2C . As an alternative, cylinder  1  may be the only deactivated cylinder during an engine cycle when engine  10  is configured as is shown in  FIG. 2C . Cylinder  2  may be the only deactivated cylinder during an engine cycle when engine  10  is configured as is shown in  FIGS. 2A, 2B, and 2C . Likewise, cylinder  3  may be the only deactivated cylinder during an engine cycle when engine  10  is configured as is shown in  FIGS. 2A, 2B, and 2C . Cylinders  200  are shown in a line. 
     Referring now to  FIG. 3B , another example cylinder deactivation pattern is shown. In  FIG. 3B , cylinders  2  and  3  of engine  10  is shown with Xs through them to indicate that cylinder  2  and  3  may be deactivated during an engine cycle while cylinders  1  and  4  remain active. Active cylinders are shown without Xs to indicate the cylinders are active. Cylinders  2  and  3  may be deactivated during an engine cycle via the systems shown in  FIGS. 2A, 2B, and 2C . As an alternative, cylinders  1  and  4  may be the only deactivated cylinder during an engine cycle when engine  10  is configured as is shown in  FIG. 2C . Deactivated cylinders shown in  FIGS. 2 and 3  are cylinders where valves are closed to prevent flow from the engine intake manifold to the engine exhaust manifold while the engine rotates and where fuel injection ceases to the deactivated cylinders. Spark provided to deactivated cylinders may also cease. Cylinders  200  are shown in a line. 
     In this way, individual cylinders or cylinder groups may be deactivated. Further, deactivated cylinders may be reactivated from time to time to reduce the possibility of engine oil seeping into engine cylinders. For example, a cylinder may fire 1-4-1-4-1-4-2-1-4-3-1-4-1-4 to reduce the possibility of oil seeping into cylinders  2  and  3  after cylinders  2  and  3  have been deactivated. 
     Referring now to  FIG. 4A , another example configuration of engine  10  is shown. Portions of the engine&#39;s combustion chambers formed in cylinder heads  35  and  35   a , which also may be referred to as part of a cylinder, are numbered from  1 - 8  according to cylinder numbers  1 - 8  as indicated for each engine cylinder. Engine  10  includes a first bank of cylinders  401  including cylinders  1 - 4  in cylinder head casting  35  and a second bank of cylinders  402  including cylinders  5 - 8  in cylinder head casting  35   a . In this configuration, engine  10  is a V eight engine that includes deactivating intake valves  208  and non-deactivating intake valves  206 . Engine  10  also includes deactivating exhaust valves  204  and non-deactivating exhaust valves  202 . The valves control air flow from the engine intake manifold to the engine exhaust manifold via engine cylinders  200 . In some examples, deactivating exhaust valves  204  may be replaced with non-deactivating exhaust valves  202  to reduce system expense while preserving the capacity to deactivate engine cylinders (e.g., cease fuel flow to the deactivated cylinder and cease air flow from an engine intake manifold to engine exhaust manifold via a cylinder while the engine rotates). Thus, in some examples, engine  10  may include only non-deactivating exhaust valves  202  in combination with deactivating intake valves  208  and non-deactivating intake valves  206 . 
     In this example, cylinders  5 ,  2 ,  3 , and  8  are shown as cylinders that have valves that are always active so that air flows from the engine intake manifold to the engine exhaust manifold as the engine rotates via cylinders  5 ,  2 ,  3 , and  8 . Cylinders  1 ,  6 ,  7 , and  4  are shown as cylinders that have valves that may be selectively deactivated in closed positions so that air does not flow from the engine intake manifold to the engine exhaust manifold via cylinders  1 ,  6 ,  7 , and  4  respectively when valves in the respective cylinders are deactivated in a closed state during an engine cycle. In other examples, such as  FIG. 4B , the cylinders that have valves that are always active are cylinders  5  and  2 . The actual total number of cylinders that have valves that are always active may be based on vehicle mass and engine displacement or other considerations. 
     Valves  202 ,  204 ,  206 , and  208  are opened and closed via a single camshaft  420 . The valves  202 ,  204 ,  206 , and  208  may be in mechanical communication with sole camshaft  320  via pushrods and conventional lash adjusters or deactivating adjusters or hydraulic cylinders as shown in U.S. Patent Publication No. 2003/0145722, entitled “Hydraulic Cylinder Deactivation with Rotary Sleeves,” filed Feb. 1, 2002 and hereby fully incorporated by reference for all purposes. Alternatively, valves  202 ,  204 ,  206 , and  208  may be operated via conventional roller cam followers and/or via valve operators as shown in  FIGS. 6A, 6B, and 5C . In still other examples, valves may be deactivated via sleeved cam lobes as shown in U.S. Patent Publication No. 2014/0303873. 
     Camshaft  420  is shown in mechanical communication with non-deactivating exhaust valves  202  via non-deactivating exhaust valve operators  250 . Camshaft  420  is also in mechanical communication with non-deactivating intake valves  206  via non-deactivating intake valve operators  251 . Camshaft  420  is also in mechanical communication with deactivating intake valves  208  deactivating intake valve operators  253 . Camshaft  420  is also in mechanical communication with deactivating exhaust valves  204  via deactivating intake valve operators  252 . Some intake and exhaust valves are not shown with valve operators to reduce busyness in the figure, but each valve is accompanied by a valve operator (e.g., non-deactivating valves are accompanied with non-deactivating valve operators and deactivating valves are accompanied with deactivating valve operators). 
     Referring now to  FIG. 4B , another example configuration of engine  10  is shown. Portions of the engine&#39;s combustion chambers formed in cylinder heads  35  and  35   a , which also may be referred to as part of a cylinder, are numbered from  1 - 8  according to cylinder numbers  1 - 8  as indicated for each engine cylinder. Engine  10  includes a first bank of cylinders  401  including cylinders  1 - 4  in cylinder head casting  35  and a second bank of cylinders  402  including cylinders  5 - 8  in cylinder head casting  35   a . In this configuration, engine  10  is also a V eight engine that includes deactivating intake valves  208  and non-deactivating intake valves  206 . Engine  10  also includes deactivating exhaust valves  204  and non-deactivating exhaust valves  202 . The valves control air flow from the engine intake manifold to the engine exhaust manifold via engine cylinders  200 . Valves  202 ,  204 ,  206 , and  208  are operated via intake camshaft  51  and exhaust camshaft  53 . Each cylinder bank includes an intake camshaft  51  and an exhaust camshaft  53 . 
     In some examples, deactivating exhaust valves may be replaced with non-deactivating exhaust valves  204  to reduce system expense while preserving the capacity to deactivate engine cylinders (e.g., cease fuel flow to the deactivated cylinder and cease air flow from an engine intake manifold to engine exhaust manifold via a cylinder while the engine rotates). Thus, in some examples, engine  10  may include only non-deactivating exhaust valves  202  in combination with deactivating intake valves  208  and non-deactivating intake valves  206 . 
     In this example, cylinders  5  and  2  are shown as cylinders that have valves that are always active so that air flows from the engine intake manifold to the engine exhaust manifold as the engine rotates via cylinders  5  and  2 . Cylinders  1 ,  3 ,  4 ,  6 ,  7 , and  8  are shown as cylinders that have intake and exhaust valves that may be selectively deactivated in closed positions so that air does not flow from the engine intake manifold to the engine exhaust manifold via cylinders  1 ,  3 ,  4 ,  6 ,  7 , and  8  respectively when valves in the respective cylinders are deactivated in a closed state. In this example, cylinders are deactivated by deactivating intake and exhaust valves of the cylinder being deactivated. For example, cylinder  3  may be deactivated so that air does not flow through cylinder  3  via deactivating valves  208  and  204 . 
     Valves  202 ,  204 ,  206 , and  208  are opened and closed via four camshafts. The valves  202 ,  204 ,  206 , and  208  may be in mechanical communication with a camshaft via valve operators shown in  FIGS. 6A, 6B, and 5C  or hydraulic cylinders or tappets, which may deactivate the valves. The engines shown in  FIGS. 4A and 4B  have a firing order of 1-5-4-2-6-3-7-8. 
     Engine  10  is also shown with first knock sensor  420 , second knock sensor  421 , third knock sensor  422 , and fourth knock sensor  423 . Thus, first cylinder bank  401  includes first knock sensor  420  and second knock sensor  421 . First knock sensor  420  may detect knock in cylinder numbers  1  and  2 . Second knock sensor  421  may detect knock in cylinder numbers  3  and  4 . Second cylinder bank  402  includes third knock sensor  422  and fourth knock sensor  423 . Third knock sensor  422  may detect knock in cylinders  5  and  6 . Fourth knock sensor  423  may detect knock in cylinders  7  and  8 . 
     Exhaust camshaft  53  is shown in mechanical communication with non-deactivating exhaust valves  202  via non-deactivating exhaust valve operators  250 . Intake camshaft  51  is in mechanical communication with non-deactivating intake valves  206  via non-deactivating intake valve operators  251 . Exhaust camshaft  53  is also in mechanical communication with deactivating exhaust valves  204  deactivating intake valve operators  252 . Intake camshaft  51  is also in mechanical communication with deactivating intake valves  208  via deactivating intake valve operators  253 . Some intake and exhaust valves are not shown with valve operators to reduce busyness in the figure, but each valve is accompanied by a valve operator (e.g., non-deactivating valves are accompanied with non-deactivating valve operators and deactivating valves are accompanied with deactivating valve operators). 
     The cylinder head configuration shown in  FIG. 4B  may be incorporated in vehicles of lower mass than the vehicles in which the cylinder head configuration shown in  FIG. 4A  is included. The configuration of  FIG. 4B  may be incorporated in vehicle of low mass since lower mass vehicles may only use two cylinders to cruise at a steady highway speed. Conversely, the configuration of  FIG. 4A  may be incorporated in vehicles of higher mass since vehicle&#39;s having a higher mass may use four cylinders to cruise at a steady highway speed. Likewise, the cylinder heads shown in  FIGS. 2A-2F  that have lower actual total numbers of cylinders that are not deactivating may be incorporated into lower mass vehicles. The cylinder heads shown in  FIGS. 2A-2F  that have higher actual total numbers of cylinders that are not deactivating may be incorporated into higher mass vehicles. Additionally, the number of cylinders in cylinder head castings shown in  FIGS. 2A-4C  that are not deactivating cylinders may be based on the vehicle&#39;s axle ratio. For example, if a vehicle has a lower axle ratio (e.g., 2.69:1 versus 3.73:1), a cylinder head configuration with a lower actual total number of cylinders that are not deactivating may be selected so that highway cruising efficiency may be improved. Thus, different vehicles with different masses and axle ratios may include a same engine block and cylinder head castings, but the actual total number of deactivating and non-deactivating valve operators may be different between the different vehicles. 
     Referring now to  FIG. 4C , another example configuration of engine  10  is shown. Portions of the engine&#39;s combustion chambers formed in cylinder heads  35  and  35   a , which also may be referred to as part of a cylinder, are numbered from  1 - 8  according to cylinder numbers  1 - 8  as indicated for each engine cylinder. Engine  10  includes a first bank of cylinders  401  including cylinders  1 - 4  in cylinder head casting  35  and a second bank of cylinders  402  including cylinders  5 - 8  in cylinder head casting  35   a . In this configuration, engine  10  is also a V eight engine that includes deactivating intake valves  208  and non-deactivating intake valves  206 . Engine  10  also includes non-deactivating exhaust valves  202 . The valves control air flow from the engine intake manifold to the engine exhaust manifold via engine cylinders  200 . Valves  202 ,  206 , and  208  are operated via intake camshaft  51  and exhaust camshaft  53 . Each cylinder bank includes an intake camshaft  51  and an exhaust camshaft  53 . 
     In this example, all engine exhaust valves  202  are non-deactivating. Exhaust camshaft  53  is shown in mechanical communication with non-deactivating exhaust valves  202  via non-deactivating exhaust valve operators  250 . Intake camshaft  51  is in mechanical communication with non-deactivating intake valves  206  via non-deactivating intake valve operators  251 . Intake camshaft  51  is also in mechanical communication with deactivating intake valves  208  via deactivating intake valve operators  253 . Some intake and exhaust valves are not shown with valve operators to reduce busyness in the figure, but each valve is accompanied by a valve operator (e.g., non-deactivating valves are accompanied with non-deactivating valve operators and deactivating valves are accompanied with deactivating valve operators). 
     The deactivating valve operators shown in  FIGS. 4A-4C  may be a lever type (e.g., see  FIG. 6B ), a sleeve type (e.g., see U.S. Patent Publication No. 2014/0303873, U.S. patent application Ser. No. 14/105,000, entitled “Position Detection For Lobe Switching Camshaft System,” filed Dec. 12, 2013 and hereby fully incorporated by reference for all purposes), a cam lobe type, or a lash adjuster type. Further, each of the cylinder heads shown in  FIGS. 4A-4C  may be mechanically coupled to a same block  33  shown in  FIG. 1A . The cylinder heads  35  shown in  FIGS. 4A-4C  may be formed from a same casting and the deactivating and non-deactivating valve operators for each cylinder head configuration may be varied as shown in  FIGS. 4A-4C . Likewise, the cylinder heads  35   a  shown in  FIGS. 4A-4C  may be formed from a same casting and the deactivating and non-deactivating valve operators for each cylinder head configuration may be varied as shown in  FIGS. 4A-4C . 
     Referring now to  FIG. 5A , an example valve operating system is shown. The depicted embodiment may represent a mechanism for an inline four cylinder engine or one of two mechanisms for a V-8 engine. Similar mechanisms with for different numbers of engine cylinders are possible. Valve operating system  500  includes an intake camshaft  51  and an exhaust camshaft  53 . Chain, gear, or belt,  599  mechanically couples camshaft  51  and camshaft  53  so that they rotate together at a same speed. In particular, chain  599  mechanically couples sprocket  520  to sprocket  503 . 
     Exhaust camshaft  53  includes cylindrical journals  504   a ,  504   b ,  504   c , and  504   d  that rotate within respective valve bodies  501   a ,  501   b ,  501   c , and  501   d . Valve bodies  501   a ,  501   b ,  501   c , and  501   d  are shown incorporated into exhaust camshaft saddle  502 , which may be part of cylinder head casting  35 . Discontinuous metering grooves  571   a ,  571   b ,  571   c , and  571   d  are incorporated into journals  504   a ,  504   b ,  504   c , and  504   d . Discontinuous metering grooves  571   a ,  571   b ,  571   c , and  571   d  may be aligned with crankshaft  40  shown in  FIG. 1A  to allow oil flow through journals  504   a ,  504   b ,  504   c , and  504   d  coincident with a desired engine crankshaft angle range so that exhaust valve operators shown in  FIG. 5B  are deactivated at a desired crankshaft angle, thereby ceasing airflow from engine cylinders. Lands  505   a ,  505   b ,  505   c , and  505   d  prevent oil flow to valve operators shown in  FIG. 5B  when the respective lands cover respective valve body outlets  506 ,  508 ,  510 , and  512 . 
     Oil may flow to valve operators shown in  FIG. 5B  via valve body outlets  506 ,  508   510  and  512 . Pressurized oil from oil pump  580  may selectively pass through valve body inlets  570 ,  572 ,  574 , and  576 ; metering grooves  571   a ,  571   b ,  571   c , and  571   d ; and valve body outlets when lands are not blocking valve body inlets and outlets  506 ,  508 ,  510  and  512 . The pressurized oil may deactivate valve operators as described in further detail below. Lands  505   a ,  505   b ,  505   c , and  505   d  selectively open and close access to valve bodies  501   a ,  501   b ,  501   c , and  501   d  for pressurized oil from oil pump  580  as exhaust camshaft  53  rotates. Exhaust camshaft  53  also includes cam lobes  507   a ,  507   b ,  509   a ,  509   b ,  511   a ,  511   b ,  513   a , and  513   b  to open and close exhaust valves as lobe lift increases and decreases in response to exhaust camshaft rotation. 
     In one example, pressurized oil selectively flows through metering groove  571   a  via valve body inlet  570  to exhaust valve operators for cylinder number one. Cam lobes  507   a  and  507   b  may provide mechanical force to lift exhaust valves of cylinder number one of a four or eight cylinder engine as exhaust camshaft  53  rotates. Similarly, pressurized oil selectively flows through metering groove  571   b  via valve body inlet  572  to exhaust valve operators for cylinder number two. Cam lobes  509   a  and  509   b  may provide mechanical force to lift exhaust valves of cylinder number two of the four or eight cylinder engine as exhaust camshaft  53  rotates. Likewise, pressurized oil selectively flows through metering groove  571   c  via valve body inlet  574  to exhaust valve operators for cylinder number three. Cam lobes  511   a  and  511   b  may provide mechanical force to lift exhaust valves of cylinder number three of a four or eight cylinder engine as exhaust camshaft  53  rotates. Also, pressurized oil selectively flows through metering groove  571   d  via valve body inlet  576  to exhaust valve operators for cylinder number four. Cam lobes  513   a  and  513   b  may provide mechanical force to lift exhaust valves of cylinder number four of a four or eight cylinder engine as exhaust camshaft  53  rotates. Thus, exhaust camshaft  53  may provide force to open poppet valves of a cylinder bank. 
     Intake camshaft  51  includes cylindrical journals  521   a ,  521   b ,  521   c , and  521   d  that rotate within respective valve bodies  540   a ,  540   b ,  540   c , and  540   d . Valve bodies  540   a ,  540   b ,  540   c , and  540   d  are shown incorporated into intake camshaft saddle  522 , which may be part of cylinder head casting  35 . Continuous metering grooves  551   a ,  551   b ,  551   c , and  551   d  are incorporated into journals  521   a ,  521   b ,  521   c , and  521   d . However, in some examples, continuous metering grooves  551   a ,  551   b ,  551   c , and  551   d  may be eliminated and oil may be supplied directly from pump  580  to intake valve operators. 
     Pressurized oil flows from oil pump  580  via passage or gallery  581  to control valves  586 ,  587 ,  588 , and  589 . Control valve  586  may be opened to allow oil to flow into valve body inlet  550 , metering groove  551   a , and valve body outlet  520   a  before oil flows to cylinder number one intake valve operators via passage  520   b . Pressurized oil is also supplied to inlet  570  via passage or conduit  524   c . Thus, by closing valve  586 , deactivation of intake valves and exhaust valves of cylinder number one may be prevented. Outlet  506  supplies oil to accumulator  506   b  and to exhaust valve operators for cylinder number one. 
     Selective operation of intake and exhaust valves for cylinder number two is similar to selective operation of intake and exhaust valves for cylinder number one. Specifically, pressurized oil flows from oil pump  580  via passage or gallery  581  to valve  587 , which may be opened to allow oil to flow into valve body inlet  552 , metering groove  551   b , and valve body outlet  524   a  before oil flows to cylinder number two intake valve operators via passage  524   b . Pressurized oil is also supplied to valve body inlet  572  via passage or conduit  524   c . Thus, by closing valve  587 , deactivation of intake valves and exhaust valves of cylinder number two may be prevented. Outlet  508  supplies oil to accumulator  508   b  and to exhaust valve operators for cylinder number two. 
     Selective operation of intake and exhaust valves for cylinder number three is similar to selective operation of intake and exhaust valves for cylinder number one. For example, pressurized oil flows from oil pump  580  via passage or gallery  581  to valve  588 , which may be opened to allow oil to flow into valve body inlet  554 , metering groove  551   c , and valve body outlet  526   a  before oil flows to cylinder number three intake valve operators via passage  526   b . Pressurized oil is also supplied to valve body inlet  574  via passage or conduit  526   c . Thus, by closing valve  588 , deactivation of intake valves and exhaust valves of cylinder number three may be prevented. Outlet  510  supplies oil to accumulator  510   b  and to exhaust valve operators for cylinder number three. 
     Selective operation of intake and exhaust valves for cylinder number four is also similar to selective operation of intake and exhaust valves for cylinder number one. In particular, pressurized oil flows from oil pump  580  via passage or gallery  581  to valve  589 , which may be opened to allow oil to flow into valve body inlet  556 , metering groove  551   d , and valve body outlet  528   a  before oil flows to cylinder number four intake valve operators via passage  528   b . Pressurized oil is also supplied to control valve body inlet  576  via passage or conduit  528   c . Thus, by closing valve  589 , deactivation of intake valves and exhaust valves of cylinder number four may be prevented. Outlet  512  supplies oil to accumulator  512   b  and to exhaust valve operators for cylinder number four. 
     Intake valve operators shown in  FIG. 5B  may be urged by cam lobes  523   a - 529   b  to operate intake valves of a bank of cylinders. In particular, cam lobes  523   a  and  523   b  respectively operate two intake valves of cylinder number one. Cam lobes  525   a  and  525   b  respectively operate two intake valves of cylinder number two. Cam lobes  527   a  and  527   b  respectively operate two intake valves of cylinder number three. Cam lobes  529   a  and  529   b  respectively operate two intake valves of cylinder number four. 
     Thus, intake and exhaust valves of a cylinder bank may be individually activated and deactivated. Further, in some examples as previously noted, oil may be supplied directly from valves  586 - 589  to intake valve operators such that continuous metering grooves  551   a - 551   d  may be omitted to reduce system cost if desired. 
     Oil pump  580  also supplies oil to cooling jet  535  to spray piston  36  shown in  FIG. 1A  via cooling jet flow control valve  534 . Oil pressure in gallery  581  may be controlled via dump valve  532  or via adjusting oil pump displacement actuator  533  which adjusts the displacement of oil pump  580 . Controller  12  shown in  FIG. 1A  may be in electrical communication with cooling jet flow control valve  534 , oil pump displacement actuator  533 , and dump valve  532 . Oil pump displacement actuator may be a solenoid valve, a linear actuator, or other known displacement actuator. 
     Referring now to  FIG. 5B , example deactivating intake valve operator  549  and exhaust valve operator  548  for the hydraulically operated valve deactivating system shown in  FIG. 5A  are shown. Intake camshaft  51  rotates so that lobe  523   a  selectively lifts intake follower  545 , which selectively opens and closes intake valve  52 . Rocker shaft  544  provides a selective mechanical linkage between intake follower  545  and intake valve contactor  547 . Passage  546  allows pressurized oil to reach a piston shown in  FIG. 5C  so that intake valve  52  may be deactivated (e.g., remain in a closed position during an engine cycle) Intake valve  52  may be activated when oil pressure in passage  546  is low. 
     Similarly, Exhaust camshaft  53  rotates so that lobe  507   a  selectively lifts exhaust follower  543 , which selectively opens and closes exhaust valve  54 . Rocker shaft  542  provides a selective mechanical linkage between exhaust follower  543  and exhaust valve contactor  540 . Passage  541  allows oil to reach a piston shown in  FIG. 5C  so that exhaust valve  54  may be activated (e.g., open and close during an engine cycle) or deactivated (e.g., remain in a closed position during an engine cycle). 
     Referring now to  FIG. 5C , an example exhaust valve operator  548  is shown Intake valve operators include similar components and operate similar to the way the exhaust valve actuator operates. Therefore, for the sake of brevity, a description of intake valve operators is omitted. 
     Exhaust follower  543  is shown with oil passage  565 , which extends within camshaft follower  564 . Oil passage  565  fluidly communicates with port  568  in rocker shaft  542 . Piston  563  and latching pin  561  selectively lock follower  543  to exhaust valve contactor  540 , which causes exhaust valve contactor  540  to move in response to the motion of follower  543  when oil is not acting on piston  563 . The exhaust valve operator  548  is in an activated state during such conditions. 
     Piston  563  may be acted upon by oil pressure within oil passages  567  and  565 . Piston  563  is forced from its at-rest position shown in  FIG. 5C  (e.g., its normally activated state) by high pressure oil in passage  565  acting against force of spring  569  to its deactivated state. Spring  565  biases piston  563  into a normally locked position that allows exhaust valve contactor  540  to operate an exhaust valve  54  when oil pressure in passage  565  is low. 
     Latching pin  561  stops at a position (e.g., unlocked position) where follower  543  is no longer locked to exhaust valve contactor  540 , thereby deactivating exhaust valve  54  when normally locked latching pin  561  is fully displaced by high pressure oil operating on piston  563 . Camshaft follower  564  is rocked according to the movement of cam lobe  507   a  when exhaust valve operator  548  is in a deactivated state. Exhaust valve  54  and exhaust valve contactor  540  remain stationary when piston latching pin  561  is in its unlocked position. 
     Thus, oil pressure may be used to selectively activate and deactivate intake and exhaust valves via intake and exhaust valve operators. Specifically, intake and exhaust valves may be deactivated by allowing oil to flow to the intake and exhaust valve operators. It should be noted that intake and exhaust valve operators may be activated and deactivated via the mechanism shown in  FIG. 5C .  FIGS. 5B and 5C  depict rocker shaft mounted deactivating valve actuators. Other types of deactivating valve actuators are possible and compatible with the invention including deactivating roller finger followers, deactivating lifters, or deactivating lash adjusters. 
     Referring now to  FIG. 5D , a valve and cylinder deactivation sequence for the mechanism of  FIGS. 5A-5C  is shown. The valve deactivation sequence may be provided by the system of  FIGS. 1A and 5A-5C . 
     The first plot from the top of  FIG. 5D  is a plot of exhaust cam groove width versus crankshaft angle. The vertical axis represents exhaust camshaft groove width measured at the location of the oil outlet passage, such as passage  506  of  FIG. 5A . Groove width increases in the direction of the vertical axis arrow. The horizontal axis represents engine crankshaft angle, where zero is top-dead-center compression stroke for the cylinder whose intake and exhaust grooves are shown. In this example, the exhaust groove corresponds to  571   a  of  FIG. 5A . The crankshaft angles for the exhaust groove width are the same as the crankshaft angle in the third plot from the top of  FIG. 5D . 
     The second plot from the top of  FIG. 5D  is a plot of intake cam groove width versus crankshaft angle. The vertical axis represents intake camshaft groove width and groove width increases in the direction of the vertical axis arrow. The horizontal axis represents engine crankshaft angle, where zero is top-dead-center compression stroke for the cylinder whose intake and exhaust grooves are shown. In this example, the intake groove corresponds to  551   a  of  FIG. 5A . The crankshaft angles for the intake groove width are the same as the crankshaft angle in the third plot from the top of  FIG. 5D . 
     The third plot from the top of  FIG. 5D  is a plot of intake and exhaust valve lift versus engine crankshaft angle. The vertical axis represents valve lift and valve lift increases in the direction of the vertical axis arrow. The horizontal axis represents engine crankshaft angle and the three plots are aligned according to crankshaft angle. Thin solid line  590  represents intake valve lift for cylinder number one when its intake valve operator is activated. Thick solid line  591  represents exhaust valve lift for cylinder number one when its exhaust valve operator is activated. Thin dashed lines  592  represent intake valve lift for cylinder number one if its intake valve operator were activated. Thin dashed line  593  represents exhaust valve lift for cylinder number one if its exhaust valve operator were activated. Vertical lines A-D represent crankshaft angles of interest for the sequence. 
     The intake valve lift for cylinder number one is shown increasing and then decreasing before crankshaft angle A. An oil control valve, such as  586  of  FIG. 5A , is closed before crankshaft angle A to prevent intake and exhaust valve deactivation. The intake valve lift  590  is shown increasing during cylinder number one&#39;s intake stroke before crankshaft angle A. Pressurized oil sufficient to deactivate intake valves is not present in the continuous intake camshaft groove before crankshaft angle A. 
     At crankshaft angle A, the oil control valve (e.g.,  586  of  FIG. 5A ) may be opened to deactivate intake and exhaust valves. The continuous intake camshaft groove width is pressurized with oil after the oil control valve is opened so that the intake valve operator latching pin may be displaced while the camshaft lobe is on a base circle for the intake valve of cylinder number one. The exhaust camshaft groove  571   a  is also pressurized with oil at crankshaft angle A. Outlet passage  506  is not pressurized with oil at angle A because the land  505   a  (shown in  FIG. 5A ) covers the valve body outlet  506  (shown in  FIG. 5A ). Therefore, only the intake valve begins to be deactivated at crankshaft angle A. The intake valve operator latching pin is disengaged from its normal position before crankshaft angle C to prevent the intake valve from opening. 
     At crankshaft angle B, the land of the exhaust camshaft journal  521   a  for cylinder number one makes way for the discontinuous groove  571   a , which allows oil to reach the exhaust valve operator for cylinder number one. Oil can flow to the intake valve operator and the exhaust valve operator at crankshaft angle B, but since the exhaust valve is partially lifted at crankshaft angle B, the exhaust valve operates until the exhaust valve closes near crankshaft angle C. The exhaust valve operator latching pin is disengaged from its normally engaged position before crankshaft angle D to prevent the exhaust valve from opening. 
     At crankshaft angle C, the intake valve does not open since the intake valve operator is deactivated for the engine cycle. Further, the exhaust valve operator latching pin is disengaged from its normal position before crankshaft angle D to prevent the exhaust valve from opening. Consequently, the exhaust valve does not open for the cylinder cycle. The intake and exhaust valves may remain deactivated until the intake and exhaust operators are reactivated by reducing oil pressure to the intake and exhaust valve operators. 
     The intake and exhaust valve may be reactivated via deactivating the oil control valve  586  and allowing oil pressure in the intake and exhaust valve operators to be reduced or via dumping oil pressure from the intake and exhaust valve operators via a dump valve (not shown). 
     Oil accumulator  506   b  maintains oil pressure in oil passage  506  during the portion of the cycle after crankshaft angle D when the exhaust cam groove land blocks passage  506 . The accumulator  506   b  compensates for oil leakage through various clearances during the time when oil supply from the pump is interrupted. The oil accumulator  506   b  may include a dedicated piston and spring or may be combined with the latch pin mechanism such as the mechanism depicted in  FIG. 5C . 
     Referring now to  FIG. 6A , a camshaft for an alternative hydraulically operated valve deactivating system is shown. Camshaft  420  may be included in the engine system shown in  FIG. 4A . 
     In this example, camshaft  420  may be an intake camshaft or an exhaust camshaft or a camshaft that operates both intake and exhaust valves. The intake and exhaust valves of each engine cylinder may be individually activated and deactivated. Camshaft  420  includes sprocket  619  that allows crankshaft  40  of  FIG. 1A  to drive camshaft  420  via a chain Camshaft  420  includes four journals  605   a - 605   d , which include lands  606   a - 606   d , and discontinuous grooves  608   a - 608   d . Camshaft saddle  602  includes stationary grooves  610   a  (shown in  FIG. 6B ) for each of valve bodies  670   a ,  670   b ,  670   c , and  670   d . The stationary grooves  610   a  are situated to axially align with discontinuous grooves  608   a - 608   d . Camshaft  420  also includes cam lobes. In one example, camshaft  420  may operate both intake and exhaust valves as camshaft  420  rotates. In particular, lobe  620  operates an intake valve of cylinder number one and lobe  622  operates an exhaust valve of cylinder number one. Lobe  638  operates an intake valve of cylinder number two and lobe  639  operates an exhaust valve of cylinder number two. Lobe  648  operates an intake valve of cylinder number three and lobe  649  operates an exhaust valve of cylinder number three. Lobe  658  operates an intake valve of cylinder number four and lobe  659  operates an exhaust valve of cylinder number four. 
     Camshaft saddle  602  includes valve bodies  670   a ,  670   b ,  670   c , and  670   d  to support and provide oil passages leading to camshaft grooves. In particular, valve body  670   a  includes inlet  613 , first outlet  612 , and second outlet  616 . First outlet  612  provides oil to exhaust valve operators. Second outlet  616  provides oil to intake valve operators. Valve body  670   b  includes inlet  633 , first outlet  636 , and second outlet  632 . First outlet  636  provides oil to exhaust valve operators. Second outlet  632  provides oil to intake valve operators. Valve body  670   c  includes inlet  643 , first outlet  646 , and second outlet  642 . First outlet  646  provides oil to exhaust valve operators. Second outlet  642  provides oil to intake valve operators. Valve body  670   d  includes inlet  653 , first outlet  656 , and second outlet  652 . First outlet  656  provides oil to exhaust valve operators. Second outlet  652  provides oil to intake valve operators. Passages  616 ,  632 ,  642 , and  652  supply pressurize oil from oil pump  690  to intake valve operators  649  (shown in  FIG. 6C ) via gallery or passage  692  for respective cylinder numbers  1 - 4  when control valves  614 ,  634 ,  644 , and  654  are activated and open. Outlets  612 ,  636 ,  646 , and  656  may supply oil pressure to exhaust valve operators  648  (shown in  FIG. 6C ) when control valves  614 ,  634 ,  644 , and  654  are open. Discontinuous grooves  608   a - 608   d  selectively provide an oil path between inlets  613 ,  633 ,  643 , and  653  and valve body outlets  612 ,  636 ,  646 , and  656  that lead to exhaust valve operators. Journals  605   a - 605   d  are partially circumscribed by discontinuous grooves  608   a - 608   d . Accumulators  609   a - 609   d  provide oil to keep exhaust valves deactivated when land  606   a  covers passage  612  for short periods of time. 
     Referring now to  FIG. 6B , a cross section valve body  670   a  and its associated components is shown. Camshaft  420  is coupled to camshaft saddle  602  via cap  699 . Cap covers stationary groove  610   a  formed in camshaft saddle  602 . Camshaft  420  includes discontinuous groove  608   a  that is axially aligned with stationary groove  610   a . Valve  614  selectively allows oil to flow to intake valve operators via passage  616  and into stationary groove  610   a . Land  606   a  selectively covers and uncovers outlet  612  which provides oil to accumulator  609   a  and exhaust valve operators as camshaft  420  rotates. 
     Referring now to  FIG. 6C , example deactivating intake valve operator  649  and deactivating exhaust valve operator  648  for the hydraulically operated valve deactivating system shown in  FIG. 6A  are shown. Camshaft  420  rotates so that lobe  620  selectively lifts intake follower  645 , which selectively opens and closes intake valve  52 . Rocker shaft  644  provides a selective mechanical linkage between intake follower  645  and intake valve contactor  647 . The intake valve operator  649  and the exhaust valve operator  648  include the components and operate as the operator described in  FIG. 5C . Passage  646  allows pressurized oil to reach a piston shown in  FIG. 5C  so that intake valve  52  may be deactivated (e.g., remain in a closed position during an engine cycle) Intake valve  52  may be activated (e.g., open and close during an engine cycle) when oil pressure in passage  646  is low. 
     Similarly, cam lobe  622  rotates to selectively lifts exhaust follower  643 , which selectively opens and closes exhaust valve  54 . Rocker shaft  642  provides a selective mechanical linkage between exhaust follower  643  and exhaust valve contactor  640 . Passage  641  allows oil to reach a piston shown in  FIG. 5C  so that exhaust valve  54  may be deactivated (e.g., remain in a closed position during an engine cycle). Low oil pressure in passage  641  activates (e.g., open and close during an engine cycle) exhaust valve  54  when piston  563  shown in  FIG. 5C  is returned to its normal or base position via spring  569 . 
     In this way, a single cam may operate intake and exhaust valves. Further, the intake and exhaust valves that are driven via the single cam may be deactivated via the intake and exhaust valve operators  648  and  649 . 
     Referring now to  FIG. 6D , a valve and cylinder deactivation sequence for the mechanism of  FIGS. 6A-6C  is shown. The valve deactivation sequence may be provided by the system of  FIGS. 1A and 6A-6C . 
     The first plot from the top of  FIG. 6D  is a plot of exhaust cam groove width at the passage leading to the exhaust valve operator versus crankshaft angle. The vertical axis represents exhaust camshaft groove width and groove width increases in the direction of the vertical axis arrow. The horizontal axis represents engine crankshaft angle, where zero is top-dead-center compression stroke for the cylinder whose intake and exhaust grooves are shown. In this example, the exhaust groove corresponds to the width of groove  608   a  of  FIG. 6A  measured at the oil outlet passage  612 . The crankshaft angles for the exhaust groove width are the same as the crankshaft angle in the third plot from the top of  FIG. 6D . 
     The second plot from the top of  FIG. 6D  is a plot of intake and exhaust valve lift versus engine crankshaft angle. The vertical axis represents valve lift and valve lift increases in the direction of the vertical axis arrow. The horizontal axis represents engine crankshaft angle and the three plots are aligned according to crankshaft angle. Thin solid line  690  represents intake valve lift for cylinder number one when its intake valve operator is activated. Thick solid line  691  represents exhaust valve lift for cylinder number one when its exhaust valve operator is activated. Thin dashed lines  692  represent intake valve lift for cylinder number one if its intake valve operator were activated. Thin dashed line  693  represents exhaust valve lift for cylinder number one if its exhaust valve operator were activated. Vertical lines A-D represent crankshaft angles of interest for the sequence. 
     The intake valve lift for cylinder number one is shown increasing and then decreasing before crankshaft angle A. An oil control valve, such as  614  of  FIG. 6A , is closed before crankshaft angle A to prevent intake and exhaust valve deactivation. The intake valve lift  690  is shown increasing during cylinder number one&#39;s intake stroke before crankshaft angle A. Pressurized oil sufficient to deactivate intake valves is not present in the continuous intake camshaft groove before crankshaft angle A. 
     At crankshaft angle A, the oil control valve (e.g.,  614  of  FIG. 6A ) may be opened to deactivate intake and exhaust valves. The stationary groove width (e.g.,  608   a  of  FIG. 6B ) and passage  616  are pressurized with oil after the oil control valve is opened so that the intake valve operator latching pin may be displaced while the outlet  616  is covered via land  606   a . Thus, outlet passage  616  is not pressurized with oil at angle A because the land  606   a  (shown in  FIG. 6A ) covers the valve body outlet  616 . Therefore, only the intake valve begins to be deactivated at crankshaft angle A. The intake valve operator latching pin is disengaged from its normal position before crankshaft angle C to prevent the intake valve from opening. 
     At crankshaft angle B, the land of the exhaust camshaft land  606   a  for cylinder number one makes way for the discontinuous groove  608   a , which allows oil to reach the outlet  616  and exhaust valve operator for cylinder number one. Oil can flow to the intake valve operator and the exhaust valve operator at crankshaft angle B, but since the exhaust valve is partially lifted at crankshaft angle B, the exhaust valve operates until the exhaust valve closes near crankshaft angle C. The exhaust valve operator latching pin is disengaged from its normally engaged position before crankshaft angle D to prevent the exhaust valve from opening. 
     At crankshaft angle C, the intake valve does not open since the intake valve operator is deactivated for the engine cycle. Further, the exhaust valve operator latching pin is disengaged from its normal position before crankshaft angle D to prevent the exhaust valve from opening. Consequently, the exhaust valve does not open for the cylinder cycle. The intake and exhaust valves may remain deactivated until the intake and exhaust operators are reactivated by reducing oil pressure to the intake and exhaust valve operators. 
     The intake and exhaust valve may be reactivated via deactivating the oil control valve  614  and allowing oil pressure in the intake and exhaust valve operators to be reduced or via dumping oil pressure from the intake and exhaust valve operators via a dump valve (not shown). 
     Oil accumulator  609   a  maintains oil pressure in oil passage  616  during the portion of the cycle after crankshaft angle D when the exhaust cam groove land blocks passage  616 . The accumulator  609   a  compensates for oil leakage through various clearances during the time when oil supply from the pump is interrupted. The oil accumulator  609   a  may include a dedicated piston and spring or may be combined with the latch pin mechanism such as the mechanism depicted in  FIG. 5C . 
     Thus, the systems of  FIGS. 1A-6D  provide for a vehicle system, comprising: an engine; and a controller including non-transitory executable instructions, which when executed by the controller, cause the controller to vary an actual total number of cylinders combusting air and fuel in the engine at an engine speed and load, varying which cylinders combust air and fuel at the engine speed and load, and adjust spark timing of the engine in response to output of a first knock sensor when a cylinder is deactivated via ceasing fuel injection and not air flow to the cylinder, and further instructions to adjust spark timing of the engine in response to output of a second knock sensor when the cylinder is deactivated via ceasing fuel injection and air flow to the cylinder. The vehicle system includes where the first knock sensor and the second knock sensor are selected based on output of an engine knock sensor to activated cylinder map. The vehicle system includes where the first knock sensor and the second knock sensor are selected based on output of an engine knock sensor to deactivated cylinder map. 
     In some examples, the vehicle system further comprises additional instructions to vary the actual total number of cylinders in response to an actual total number of engine revolutions. The vehicle system further comprises additional instructions to vary which cylinders combust air and fuel in response to an actual total number of engine revolutions. The vehicle system further comprises additional instructions to adjust a knock sensitivity threshold for a cylinder to a first level in response to sensing knock via the first knock sensor, and additional instructions to adjust the knock sensitivity threshold for the cylinder to a second level in response to sensing knock via the second knock sensor. 
     It should be noted that the systems of  FIGS. 1A-6D  may be operated to provide a desired engine torque where an actual total number of active cylinders may remain the same while the active cylinders that form the actual total number of active cylinders may change from engine cycle to engine cycle. In addition, the actual total number of cylinders combusting air and fuel during an engine cycle to produce the desired engine torque may change from engine cycle to engine cycle, if desired. This may be referred to as a rolling variable displacement engine. For example, a four cylinder engine having a firing order of 1-3-4-2 may fire cylinders  1  and  3  during a first engine cycle, cylinders  3  and  2  during a next engine cycle, cylinders  1 - 3 - 2  during a next engine cycle, cylinders  3 - 4 - 2  during a next engine cycle, and so on to provide a constant desired engine torque. 
     Referring now to  FIG. 7 , a method for operating an engine with deactivating cylinders and valves is shown. The method of  FIG. 7  may be included in the system described in  FIGS. 1A-6C . The method may be included as executable instructions stored in non-transitory memory. The method of  FIG. 7  may perform in cooperation with system hardware and other methods described herein to transform an operating state of an engine or its components. 
     At  702 , method  700  determines the engine hardware configuration. In one example, the engine hardware configuration may be stored in memory at a time of manufacture. The engine hardware configuration information may include but is not limited to information describing a total actual number of engine cylinders, a total actual number of engine cylinders that do not include deactivating intake and exhaust valves, an actual total number of engine cylinders that include deactivating exhaust valves, an actual total number of engine cylinders that include deactivating intake valves, identities (e.g., cylinder numbers) of cylinders that include deactivating intake valves, identities of cylinders that include deactivating exhaust valves, identities of cylinders that do not include deactivating intake and exhaust valves, engine knock sensor locations, an actual total number of engine knock sensors, and other system configuration parameters. Method  700  reads the vehicle configuration information from memory and proceeds to  704 . 
     At  704 , method  700  judges if cylinder deactivation via deactivating intake and/or exhaust valves is available given the system configuration information retrieved at  702 . If method  700  judges that cylinder deactivation is not available or possible via intake and/or exhaust valves, the answer is no and method  700  proceeds to exit. Otherwise, the answer is yes and method  700  proceeds to  706 . 
     At  706 , method  700  judges if only intake only cylinder deactivation is available. In other words, method  700  judges if only intake valves of engine cylinders may be deactivated (e.g., held in a closed state throughout an engine cycle) to deactivate cylinders while all exhaust valves of all engine cylinders continue to operate as an engine rotates. In some engine configurations it may be desirable to deactivate only intake valves of cylinders being deactivated to reduce system cost.  FIGS. 2B and 2C  show two examples of such an engine configuration. Cylinder intake and exhaust valves may be deactivated in a closed state where they do not open from a closed position over an engine cycle. Method  700  may judge that only intake valves of engine cylinders may be deactivated to deactivate engine cylinders while all engine exhaust valves of engine cylinders continue to operate as the engine rotates based on the hardware configuration determined at  702 . If method  700  judges that only intake valves of engine cylinders may be deactivated to deactivate engine cylinders while all engine exhaust valves of engine cylinders continue to operate as the engine rotates, the answer is yes and method  700  proceeds to  708 . Otherwise, the answer is no and method  700  proceeds to  710 . 
     At  708 , method  700  determines engine cylinders in which intake valves may be deactivated and exhaust valves continue to operate as the engine rotates. Method may determine engine cylinders in which intake valves may be deactivated while exhaust valves continue to operate based on the method of  FIG. 8 . Method  700  proceeds to  712  after engine cylinders in which intake valves may be deactivated are determined. 
     At  710 , method  700  determines engine cylinders in which intake valves and exhaust valves may be deactivated as the engine rotates. Method may determine engine cylinders in which intake and exhaust valves may be deactivated based on the method of  FIG. 10 . Method  700  proceeds to  712  after engine cylinders in which intake and exhaust valves may be deactivated are determined. 
     At  712 , method  700  determines the allowed or allowable cylinder modes for operating the engine. A cylinder mode identifies how many engine cylinders are active and which cylinders are active (e.g., cylinder number  1 ,  3 , and  4 ). Method  700  determines the allowed cylinder modes according to the method of  FIG. 11 . Method  700  proceeds to  714  after the allowed cylinder modes are determined. 
     At  714 , method  700  adjusts engine oil pressure responsive to cylinder modes. Method  700  adjusts engine oil pressure according to the method of  FIG. 31 . Method  700  proceeds to  716  after engine oil pressure is adjusted. 
     At  716 , method  700  deactivates selected cylinders according to the allowed cylinder modes. Method  700  deactivates intake and/or exhaust valves to deactivate selected cylinders according to the allowed cylinder modes determined at  712 . For example, if the engine is a four cylinder engine and the allowed cylinder mode includes three active cylinders, method  700  deactivates one cylinder. The particular cylinders that are active and the cylinders that are deactivated may be based on cylinder modes. The cylinder modes may change with vehicle operating conditions so that a same actual total number of cylinders may be active and a same actual total number of cylinders may be deactivated, but the cylinders that are activated and deactivated may change from cylinder cycle to cylinder cycle. Valves operation of deactivated cylinders is based on the cylinder deactivation mode associated with the deactivated cylinder. For example, if the allowed cylinder modes include cylinder deactivation modes from the method of  FIG. 20 , the valves in deactivated cylinders may operate according to the cylinder deactivation modes described in  FIG. 20 . 
     If a plurality of actual total numbers of active cylinders is allowed, the actual total number of active cylinders in a particular cylinder mode that provides lowest fuel consumption while providing the desired driver demand torque is activated. Further, the allowed transmission gears that may be associated with the allowed cylinder mode that is activated may be engaged. 
     Method  700  may deactivate intake and/or exhaust valves via the systems described herein or via other known valve deactivation systems. If an engine knock sensor or other sensor indicates engine noise greater than a threshold or vibration greater than a threshold immediately after changing cylinder modes, a different actual total number of active cylinders and transmission gear may be selected (e.g., the transmission gear and cylinder mode prior to changing the cylinder mode, which may be a greater actual total number of active cylinders). The knock sensor may be sampled at an engine crankshaft interval outside of an engine knock window to avoid switching modes based on knock. Knock sensor output from within the knock window may be excluded for reactivating a cylinder in response to engine vibration. 
     Engine cylinders may be deactivated via holding intake valves in closed positions over an entire engine cycle. Further, injection of fuel to deactivated cylinders may also be ceased. Spark delivery to deactivated cylinders may also be ceased. In some examples, exhaust valves of cylinders being deactivated are also held in closed positions over the entire engine cycle while the intake valves are deactivated so that gases are trapped in the deactivated cylinders. Method  700  proceeds to  718  after selected engine cylinders are deactivated via intake and exhaust valves. 
     At  718 , method  700  controls engine knock responsive to cylinder deactivation. Method  700  controls engine knock according to the method of  FIGS. 33-38 . Method  700  proceeds to  720  after controlling engine knock. 
     At  720 , method  700  performs cylinder deactivation diagnostics. Method  700  performs cylinder diagnostics according to the method of  FIGS. 39-40 . Method  700  proceeds to exit after performing cylinder diagnostics. 
     Referring now to  FIG. 8A , a method to determine cylinders in which intake valves may be deactivated is shown. The method of  FIG. 8  may be included in the system described in  FIGS. 1A-6C . The method may be included as executable instructions stored in non-transitory memory. The method of  FIG. 8  may perform in cooperation with system hardware and other methods described herein to transform an operating state of an engine or its components. 
     At  802 , method  800  chooses an actual total number of cylinders for the engine. The actual total number of cylinders may be based on vehicle mass and performance requirements. In some examples, the engine will have four cylinders while in other examples the engine will have six or eight cylinders. Further, the actual total number of engine cylinders with valves that always remain active while the engine rotates is determined. In one example, the actual total number of cylinders that have valves (e.g., intake and exhaust poppet valves) that remain active while the engine rotates is based on an amount of power the vehicle requires to operate at a desired speed (e.g., 60 KPH). If the engine has the capacity to provide the amount of power with two or more cylinders, the engine may be produced with two cylinders that have valves that always remain active (e.g., opening and closing over an engine cycle). If the engine has the capacity to provide the amount of power with four or more cylinders, the engine may be produced with four cylinders that have valves that always remain active. The remaining cylinders are provided with deactivating intake valves and non-deactivating exhaust valves. Method  800  proceeds to  804  after the actual total number of engine cylinders and the actual total number of cylinders with valves that always remain active are determined. 
     At  804 , the engine is constructed with non-deactivating intake valve operators and non-deactivating exhaust valve operators in engine cylinders that always remain active while the engine rotates. The remaining engine cylinders are provided deactivating intake valve operators and non-deactivating exhaust valve operators. Method  800  proceeds to  806  after the engine is assembled with deactivating and non-deactivating valves. 
     At  806 , method  800  estimates an amount of oil in cylinders with intake valves that are deactivated during an engine cycle so that the intake valves do not open during an engine cycle or a cycle of the cylinder in which the intake valves operate. In one example, the amount of oil in engine cylinders is estimated based on the empirical model described in  FIG. 8B . Method  800  determines amounts of oil in each engine cylinder where intake valves of the cylinder are deactivated and where the cylinder is deactivated such that air flow through the cylinder is substantially ceased (e.g., less than 10% of the air flow through the cylinder at idle conditions). The amount of oil in each cylinder is revised each engine cycle. Method  800  proceeds to  808  after the oil amount in each cylinder is determined. 
     Additionally, method  800  may estimate engine oil quality at  806 . Engine oil quality may be an estimate of contaminants in the engine oil. The engine oil quality may be assigned a value from 0 to 100, zero corresponding to oil at an end of its life cycle and one hundred corresponding to fresh oil. In one example, the estimate of engine oil quality is based on engine operating time, engine load during the operating time, and engine speed during the operating time. For example, average engine load and speed may be determined over the engine operating time. The average engine load and speed index a table of empirically determined values and the table outputs an oil quality value. It may be desirable to limit an amount of time cylinder deactivation is available in response to oil quality because low oil quality may increase engine wear during cylinder deactivation and/or increase engine emissions during cylinder deactivation. 
     Method  800  may also determine an actual total number of particulate regenerations since a last time engine oil was changed. A particulate filter may be regenerated via raising particulate filter temperature and combusting carbonaceous soot stored in the particulate filter. Each time the particulate filter is regenerated after an engine oil change, an actual total number of particulate filter regenerations is increased. 
     At  808 , method  800  prevents cylinders containing more than a threshold amount of oil from being deactivated. In other words, if a cylinder with deactivated intake valves (e.g., intake valves that remain closed over an engine cycle) contains more than a threshold amount of oil, the cylinder is reactivated (e.g., cylinder intake and exhaust valves open and close during an engine cycle and air and fuel are combusted in the cylinder) so that oil entry into the cylinder may be limited. The cylinder is reactivated via activating the intake valve operator and supplying spark and fuel to the cylinder. If the cylinder is reactivated, it remains activated at least until an amount of oil in the cylinder is less than a threshold amount. Further, the amount of intake valve and exhaust valve opening time overlap may be increased in response to the amount of oil in the deactivated cylinder exceeding a threshold. By increasing intake valve and exhaust open time overlap in response to the amount of oil in a cylinder exceeding a threshold, it may be possible to evacuate oil vapors from the cylinder to improve subsequent combustion event stability and emissions. Further, one cylinder may be activated in response to an amount of oil in the one cylinder, while during a same engine cycle, a second cylinder may be deactivated so that a total actual number of active engine cylinders remains constant during an engine cycle. The cylinders may be activated and deactivated as described elsewhere herein. For example, the one cylinder may be activated via opening intake and exhaust valves during a cycle of the one cylinder. The second cylinder may be deactivated via closing and holding closed intake, or intake and exhaust valves, closed during a cycle of the second cylinder. 
     If a cylinder with deactivating intake valves and non-deactivating exhaust valves is deactivated by holding intake valves of the deactivated cylinder closed during a cycle of the deactivated cylinder, while exhaust valves continue to open and close, closing timing of exhaust valves may be adjusted in response to deactivating the cylinder so that cylinder compression and expansion losses may be reduced. Method  800  proceeds to exit after cylinders containing more than a threshold amount of oil are reactivated. 
     Additionally at  808 , cylinders may not be deactivated or may be reactivated (e.g., combusting air and fuel in the cylinders) in response to oil quality being less than a threshold value. Further, method  800  may activate engine cylinders or prevent engine cylinders from being deactivated in response to an actual total number of particulate filter regenerations since a last engine oil change being greater than a threshold. These actions may improve vehicle emissions and/or reduce engine wear. 
     Referring now to  FIG. 8B , a block diagram of an example empirical model for estimating an amount of oil in an engine cylinder is shown. An amount of oil in each deactivated cylinder may be estimated via a model similar to model  850 , although variables in the described functions or tables may have different values depending on the cylinder number. 
     Model  850  estimates a base oil amount that enters into cylinders that have deactivated intake valves (e.g., intake valves that remain in a closed position over an engine or cylinder cycle) and operating exhaust valves at block  852 . The cylinder oil amounts are empirically determined and installed into a table or function that is stored in controller memory. In one example, the table or function is indexed by engine speed and in cylinder or exhaust pressure. The table or function outputs an amount of oil in the cylinder. The amount of oil is directed to block  854 . 
     At block  854 , the amount of oil in a cylinder is multiplied by a scalar or real number that adjusts the amount of oil in response to oil temperature. Oil viscosity may vary with oil temperature and the amount of oil that may enter a deactivated cylinder may vary with oil temperature. Since oil viscosity can decrease with oil temperature, the amount of oil that may enter a deactivated cylinder may increase with increased oil temperature. In one example, block  854  includes a plurality of empirically determined scalars for different oil temperatures. The amount of oil from block  852  is multiplied by the scalar in block  854  to determine the amount of oil in the engine cylinder as a function of oil temperature. 
     At  856 , a scalar based on engine or cylinder compression ratio (CR) is multiplied by the output of block  854  to determine the amount of oil in the engine cylinder as a function of oil temperature and engine compression ratio. In one example, the amount of oil in the cylinder is increased for higher cylinder compression ratios since a vacuum is created in the cylinder after the exhaust valve closes. The value of  856  is empirically determined and stored to memory. 
     At  858 , the amount of oil in the cylinder is multiplied by a value that is a function of exhaust valve closing position or trapped cylinder volume. The value decreases as exhaust valve closing timing is retarded from top-dead-center exhaust stroke since additional volume of exhaust gas is trapped in the cylinder as exhaust valve closing retard increases. The value decreases as exhaust valve closing timing is advanced from top-dead-center exhaust stroke since additional volume of exhaust gas is trapped in the cylinder as exhaust valve closing advance increases. The function of  858  is empirically determined and stored to memory. The amount oil in the cylinder is passed to block  860 . 
     At block  860 , the amount of oil in a cylinder is multiplied by a scalar that adjusts the amount of oil in response to engine temperature. Engine temperature may affect clearances between engine components and the amount of oil that enters the cylinder may vary with engine temperature and engine component clearances. In one example, block  860  includes a plurality of empirically determined scalars for different engine temperatures. The amount of oil that enters the cylinder decreases as engine temperature increases since clearance between engine components may decrease with increasing engine temperature. Block  860  outputs an estimate of oil in an engine cylinder. 
     Referring now to  FIG. 9 , an example operating sequence for a four cylinder engine is shown. In this example, engine cylinder numbers two and three may be selectively activated and deactivated via activating and deactivating intake valves of cylinder numbers two and three. The four cylinder engine has a 1-3-4-2 firing order when it combusts air and fuel. The vertical markers at time T 0 -T 7  represent times of interest in the sequence. The plots of  FIG. 9  are time aligned and occur at the same time. 
     The first plot from the top of  FIG. 9  is a plot of estimated oil in cylinder number two versus time. The vertical axis represents an estimated amount of oil in cylinder number two and the estimated amount of oil in cylinder number two increases in the direction of the vertical axis arrow. The horizontal axis represents time and time increases from the left side of the plot to the right side of the plot. Horizontal line  902  represents a threshold limit for an amount of oil in cylinder number two which is not to be exceeded. 
     The second plot from the top of  FIG. 9  is a plot of estimated oil in cylinder number three versus time. The vertical axis represents an estimated amount of oil in cylinder number three and the estimated amount of oil in cylinder number three increases in the direction of the vertical axis arrow. The horizontal axis represents time and time increases from the left side of the plot to the right side of the plot. Horizontal line  904  represents a threshold limit for an amount of oil in cylinder number three which is not to be exceeded. 
     The third plot from the top of  FIG. 9  is a plot of the number of requested operating cylinders. The number of requested operating cylinders may be a function of driver torque demand, engine speed, and other operating conditions. The vertical axis represents the requested number of operating engine cylinders and the requested number of operating engine cylinders are shown along the vertical axis. The horizontal axis represents time and time increases from the left side of the plot to the right side of the plot. 
     The fourth plot from the top of  FIG. 9  is a plot of the operating state of cylinder number two versus time. The vertical axis represents cylinder number two operating state. Cylinder number two is operating combusting air and fuel with intake and exhaust valves opening and closing during an engine cycle when the trace is at a higher level near the vertical axis arrow. Cylinder number two is not operating and not combusting air and fuel when the trace is at a lower level near the horizontal axis. The intake valves are closed for the entire engine cycle when the trace is near the horizontal axis and exhaust valves open and close during an engine cycle when the trace is at the lower level near the horizontal axis arrow. 
     The fifth plot from the top of  FIG. 9  is a plot of the operating state of cylinder number three versus time. The vertical axis represents cylinder number three operating state. Cylinder number three is operating combusting air and fuel with intake and exhaust valves opening and closing during an engine cycle when the trace is at a higher level near the vertical axis arrow. Cylinder number three is not operating and not combusting air and fuel when the trace is at a lower level near the horizontal axis. The intake valves are closed for the entire engine cycle when the trace is near the horizontal axis and exhaust valves open and close during an engine cycle when the trace is at the lower level near the horizontal axis arrow. 
     At time T 0 , the estimated amount of oil in cylinder number two is low. The estimated amount of oil in cylinder number three is also low. The engine is operating with four active (e.g., cylinders combusting air and fuel) cylinders as indicated by the requested number of cylinders being equal to four and the operating states of cylinder number two and number three being active (e.g., cylinder operating state traces are at higher levels). Cylinder numbers one and four are active whenever the engine is miming and combusting air and fuel. 
     At time T 1 , the estimated amounts of oil in cylinder numbers two and three is low. The number of requested operating cylinders is reduced from four to three. The requested number of engine cylinders may be reduced in response to a lower driver demand torque. Cylinder number three is deactivated (e.g., combustion is stopped in cylinder number three, intake valves of cylinder number three are deactivated such that they do not open and close during an engine cycle, fuel delivery to the cylinder ceases, spark delivery to the cylinder may be ceased, and exhaust valves of cylinder number three continue to open and close during each engine cycle) in response to the requested number of cylinders being three. Cylinder number two continues to operate with active intake valves and combustion. 
     Between time T 1  and time T 2 , the estimated amount of oil in cylinder number two remains low and constant. The estimated amount of oil in cylinder number three is increasing. The amount of oil in cylinder number three increases because a vacuum may form in cylinder number three after exhaust valves of cylinder number three close because intake valves of cylinder number three are deactivated. 
     At time T 2 , the amount of oil in cylinder number three equals or exceeds threshold  904 . Therefore, cylinder number three is reactivated which increases pressure in the cylinder and pushes oil out of the cylinder past the cylinder rings, thereby reducing the amount of oil in cylinder number three. However, since the requested number of cylinders is three, cylinder number two is deactivated (e.g., combustion is stopped in cylinder number two, intake valves of cylinder number two are deactivated such that they do not open and close during an engine cycle, fuel delivery to the cylinder ceases, spark delivery to the cylinder may be ceased, and exhaust valves of cylinder number two open and close during each engine cycle). In this way, the requested number of operating cylinders is provided even when the oil amount of one cylinder is at or above a threshold limit. The estimated amount of oil in cylinder number two is at a lower level. The operating state of cylinder number two is low to indicate cylinder number two is deactivated. The operating state of cylinder number three is high to indicate cylinder number three is activated. 
     At time T 3 , the number of requested operating cylinders is two and the estimated amount of oil in cylinder number three is low. Cylinder number three is deactivated in response to the low amount of oil in cylinder number three and the number of requested operating cylinders. Cylinder number two remains in a deactivated state. The amount of oil in cylinder number two continues to increase. 
     At time T 4 , the amount of oil in cylinder number two exceeds threshold level  902  and the number of requested operating cylinders is two. Cylinder number two is reactivated to evacuate oil from cylinder number two. Cylinder number three remains deactivated so that the number of cylinders combusting is near the requested number of operating cylinders. A short time after time T 4 , cylinder number two is reactivated in response to the estimated amount of oil in cylinder number two being low. 
     At time T 5 , the amount of oil in cylinder number three exceeds threshold level  904  and the number of requested operating cylinders is two. Cylinder number three is reactivated to evacuate oil from cylinder number three. Cylinder number two remains deactivated so that the number of cylinders combusting is near the requested number of operating cylinders. A short time after time T 5 , cylinder number three is reactivated in response to the estimated amount of oil in cylinder number three being low. 
     At time T 6 , the amount of oil in cylinder number two exceeds threshold level  902  and the number of requested operating cylinders is two. Cylinder number two is reactivated to evacuate oil from cylinder number two. Cylinder number three remains deactivated so that the number of cylinders combusting is near the requested number of operating cylinders. A short time after time T 6 , cylinder number two is reactivated in response to the estimated amount of oil in cylinder number two being low. 
     At time T 7 , the requested number of operating cylinders is increased in response to an increase in driver demand torque. The operating states of cylinder numbers two and three changes to active to indicate cylinder numbers two and three have been reactivated in response to the number of operating cylinders. The estimated amount of oil in cylinder numbers two and three is reduced by activating cylinder numbers two and three. 
     In this way, engine cylinders may be selectively deactivate and activated to conserve fuel and reduce oil in engine cylinders. Further, the activated cylinders may be deactivated to reduce oil in engine cylinders and to attempt to match the requested number of operating cylinders. Activating cylinders to remove oil from cylinders has priority over deactivating cylinders to match the requested number of operating cylinders so that oil consumption may be reduced. 
     Referring now to  FIG. 10 , a method to determine cylinders in which intake valves may be deactivated is shown. The method of  FIG. 10  may be included in the system described in  FIGS. 1A-6C . The method may be included as executable instructions stored in non-transitory memory. The method of  FIG. 10  may perform in cooperation with system hardware and other methods described herein to transform an operating state of an engine or its components. 
     At  1002 , method  1000  an actual total number of cylinders for the engine is chosen. The actual total number of cylinders may be based on vehicle mass and performance requirements. In some examples, the engine will have four cylinders while in other examples the engine will have six or eight cylinders. Further, the actual total number of engine cylinders with valves that always remain active while the engine rotates is determined. In one example, the actual total number of cylinders that have valves (e.g., intake and exhaust poppet valves) that remain active while the engine rotates is based on an amount of power the vehicle requires to operate at a desired speed (e.g., 60 KPH). If the engine has the capacity to provide the amount of power with four or more cylinders, the engine may be produced with four cylinders that have valves that always remain active (e.g., opening and closing over an engine cycle). If the engine has the capacity to provide the amount of power with six or more cylinders, the engine may be produced with six cylinders that have valves that always remain active. The remaining cylinders are provided with deactivating intake valves and non-deactivating exhaust valves. Method  1000  proceeds to  1004  after the actual total number of engine cylinders and the actual total number of cylinders with valves that always remain active are determined. 
     At  1004 , the engine is constructed with non-deactivating intake valve operators and non-deactivating exhaust valve operators in engine cylinders that always remain active while the engine rotates. The remaining engine cylinders are provided deactivating intake valve operators and deactivating exhaust valve operators. Method  1000  proceeds to  1006  after the engine is assembled with deactivating and non-deactivating valves. 
     At  1006 , method  1000  estimates an amount of oil in cylinders with intake valves that are deactivated during an engine cycle so that the intake valves do not open during an engine cycle or a cycle of the cylinder in which the intake valves operate. In one example, the amount of oil in engine cylinders is estimated based on the empirical model described in  FIG. 8B ; however, the functions and/or tables described in  FIG. 8B  may include different variable values than those for an engine with cylinders that are deactivated via closing only intake valves over an engine cycle. Method  1000  determines amounts of oil in each engine cylinder where intake valves of the cylinder are deactivated and where the cylinder is deactivated such that air flow through the cylinder is substantially ceased (e.g., less than 10% of the air flow through the cylinder at idle conditions). The amount of oil in each cylinder is revised each engine cycle. Method  1000  proceeds to  1008  after the oil amount in each cylinder is determined. 
     At  1008 , method  1000  prevents cylinders containing more than a threshold amount of oil from being deactivated. In other words, if a cylinder with deactivated intake and exhaust valves (e.g., intake and exhaust valves that remain closed over an engine cycle) contains more than a threshold amount of oil, the cylinder is reactivated (e.g., cylinder intake and exhaust valves open and close during an engine cycle and air and fuel are combusted in the cylinder) so that oil entry into the cylinder may be limited. The cylinder is reactivated via activating the intake valve operator and supplying spark and fuel to the cylinder. Method  1000  proceeds to exit after cylinders containing more than a threshold amount of oil are reactivated. 
     Referring now to  FIG. 11 , a method to determine available cylinder modes for an engine is shown. The method of  FIG. 11  may be included in the system described in  FIGS. 1A-6C . The method may be included as executable instructions stored in non-transitory memory. The method of  FIG. 11  may perform in cooperation with system hardware and other methods described herein to transform an operating state of an engine or its components. 
     At  1102 , method  1100  evaluates engine cylinder mode busyness against limits to determine if changing of cylinder modes is too busy or if it is reasonable. If the cylinder mode is switched too often, the vehicle&#39;s occupants may be made aware of cylinder mode shifting such that cylinder mode shifting becomes undesirable. Method  1100  evaluates cylinder mode shifting according to the method of  FIG. 12  and proceeds to  1106 . 
     At  1106 , method  1100  evaluates which cylinder modes may provide a requested amount of engine brake torque. Method  1100  proceeds to the method of  FIG. 14  to determine which cylinder modes may provide the requested amount of engine brake torque. Method  1100  proceeds to  1108  after determining which cylinder modes may provide the requested amount of brake torque. 
     At  1108 , method  1100  evaluates if changing cylinder mode will reduce fuel consumption. Method  11  proceeds to the method of  FIG. 15  to determine if changing the cylinder mode may conserve fuel. Method  1100  proceeds to  1112  after it is determined if changing cylinder mode will conserve fuel. 
     At  1112 , method  1100  evaluates a cam phasing rate for determining the cylinder mode. The cam phasing rate is a rate that a cam torque actuated phasor changes a position of an engine&#39;s cam relative to a position of the engine&#39;s crankshaft. Because cam torque actuated variable valve timing phase actuators rely on valve spring force to operate, and because deactivating a cylinders valves reduces the reaction force provided by the valve springs, it may not be desirable to use some cylinder modes when high rates of change of cam phase is desired. Method  1100  evaluates the cam phase rate for available cylinder modes according to the method of  FIG. 16  and then proceeds to  1114 . 
     At  1114 , method  1100  evaluates different transmission gears for selecting the cylinder mode. Method  1100  evaluates different transmission gears for selecting the cylinder mode according to the method of  FIG. 18 . Method  1100  proceeds to  1116  after evaluating different transmission gears for selecting the cylinder mode. 
     At  1116 , method  1100  evaluates towing and hauling modes for selecting the cylinder mode. Method  1100  evaluates towing and hauling modes for selecting the cylinder mode according to the method of  FIG. 20 . Method  1100  proceeds to  1118  after evaluating towing and hauling modes for selecting the cylinder mode. 
     At  1118 , method  1100  judges if select conditions are present for selecting the cylinder mode. Method  1100  determines of conditions are present for determining the cylinder mode according to the method of  FIG. 22 . Method  1100  proceeds to  1120  after determining if conditions are present for selecting the cylinder mode. 
     At  1120 , method  1100  controls engine manifold absolute pressure (MAP) during conditions when one or more cylinders are being deactivated via deactivating intake and/or exhaust valves of engine cylinders. Further, fuel delivery to the cylinder and spark delivery to the cylinder are ceased when the cylinder is deactivated. Method  1100  controls MAP according to the method of  FIG. 23  and proceeds to  1121 . 
     At  1121 , method  1100  controls engine manifold absolute pressure (MAP) during conditions when one or more cylinders are being activated via activating intake and/or exhaust valves of engine cylinders. Further, fuel delivery to the cylinder and spark delivery to the cylinder are activated when the cylinder is activated. Method  1100  controls MAP according to the method of  FIG. 25  and proceeds to  1122 . 
     At  1122 , method  1100  controls engine torque during changing cylinder modes. Method  1100  controls engine torque according to the method of  FIG. 27A  before proceeding to  1124 . 
     At  1124 , method  1100  controls fuel supplied to the engine for changing cylinder modes. Method  1100  controls fuel supplied to the engine according to the method of  FIG. 29 . Method  1100  proceeds to exit after controlling fuel flow to the engine. 
     Referring now to  FIG. 12 , a method for evaluating whether or not changing the cylinder mode exceeds busyness limits is shown. The method of  FIG. 12  may be included in the system described in  FIGS. 1A-6C . The method of  FIG. 12  may be included as executable instructions stored in non-transitory memory. The method of  FIG. 12  may perform in cooperation with system hardware and other methods described herein to transform an operating state of an engine or its components. 
     At  1202 , method  1200  judges if the present execution of method  1200  is a first execution of method  1200  since the vehicle and engine were stopped and shutdown. Method  1200  may judge that the present execution of method  1200  is a first execution since the vehicle was activated after the vehicle was deactivated (e.g., stopped without intent to restart immediately). In one example, method  1200  judges that the present execution is a first execution when a value in memory is zero and the method has not been executed since a driver requested the vehicle to start via a pushbutton or key. If method  1200  judges that the present execution of method  1200  is a first execution of method  1200  since the engine was stopped, the answer is yes and method  1200  proceeds to  1220 . Otherwise, the answer is no and method  1200  proceeds to  1204 . 
     At  1220 , method  1200  determines values of variables PAYBACK_TIME and VDE_BUSY. The variable PAYBACK_TIME is an amount of time it takes in a newly selected cylinder mode or variable displacement engine (VDE) mode to cover the fuel cost of transitioning from one cylinder mode or VDE mode to the next cylinder mode or VDE mode. The fuel cost may be due to reducing engine torque via spark retard or some other adjustment to control engine torque during mode transitions. The variable VDE_BUSY is a value that is a basis for determining whether or not cylinder mode or VDE switching is occurring at a higher than desired frequency. The value is updated based on the number of cylinder mode or VDE transitions and the amount of time spent in a cylinder mode or VDE mode. VDE_BUSY is initially set to zero and PAYBACK_TIME is empirically determined and stored in memory. In one example, the variable PAYBACK_TIME may vary depending on the cylinder mode being exited and the cylinder mode being entered. There may be VDE_BUSY variables for each cylinder mode as shown in  FIG. 13 . Method  1200  proceeds to  1204  after the variable values are determined. 
     At  1204 , method  1200  judges if the engine is exiting a valve deactivation mode. Method  1200  may judge that the engine is exiting a valve deactivation mode if valves of one or more cylinders are being activated (e.g., intake valves transition from not opening and closing during an engine cycle to opening and closing during an engine cycle) in an engine cycle. If method  1200  judges that the engine is exiting a valve deactivation mode and valves of at least one cylinder are being reactivated during an engine cycle, the answer is yes and method  1200  proceeds to  1208 . Otherwise, the answer is no and method  1200  proceeds to  1230 . 
     At  1230 , method  1200  judges if the engine is operating in a valve deactivation mode. Method  1200  may judge that the engine is operating in a valve deactivation mode if intake and/or exhaust valves of an engine cylinder stay closed and do not open and close during an engine cycle. If method  1200  judges that the engine is operating in a valve deactivation mode, the answer is yes and method  1200  proceeds to  1232 . Otherwise, the answer is no and method  1200  proceeds to  1210 . 
     At  1232 , method  1200  counts an amount of time one or more cylinders have valves in a deactivated state to determine an amount of time the engine is in a deactivation mode. The engine may have more than one deactivation mode and time in each deactivation mode may be determined. For example, an eight cylinder engine may deactivate two cylinders or four cylinders to provide two deactivation modes. The first deactivation mode is where two cylinders are deactivated and the second deactivation mode is where four cylinders are deactivated. Method  1200  determines the amount of time the engine has two deactivated cylinders and the amount of time the engine has four deactivated cylinders. Method  1200  proceeds to  1210  after determining an amount of time one or more engine cylinders are in a deactivation mode. 
     At  1208 , method  1200  determines an amount of time to add or subtract from the VDE_BUSY variable based on an amount of time one or mode cylinders have deactivated valves and the PAYBACK_TIME. A larger number is added to the VDE_BUSY variable if the engine has deactivated cylinders in a mode for a short period of time relative to the PAYBACK_TIME. For example, when an eight cylinder engine operates with active valves in four cylinders for four seconds method  1200  may add a value of 120 to the VDE_BUSY variable when the variable PAYBACK_TIME is 20. On the other hand, when an eight cylinder engine operates with active valves in four cylinders for 19 seconds method  1200  may add a value of 40 to the VDE_BUSY variable when the variable PAYBACK_TIME is 20. If the eight cylinder engine operates with active valves in four cylinders for 45 seconds method  1200  may add a value of −10 to the VDE_BUSY variable when the variable PAYBACK_TIME is 20. The value added to VDE_BUSY may be a linear or non-linear function of the difference between the amount of time the engine spends in the cylinder deactivation mode and the value of PAYBACK_TIME. Method  1200  proceeds to  1210  after the value of VDE_BUSY has been adjusted. 
     At  1210 , method  1200  subtracts a predetermined amount or value from the VDE_BUSY variable. For example, method  1210  may subtract a value of 5 from the VDE_BUSY variable. By subtracting a predetermined amount from the VDE_BUSY variable, the VDE_BUSY variable may be driven toward a value of zero. The variable VDE_BUSY is limited to positive values greater than zero. Method  1200  proceeds to  1212  after subtracting the predetermined amount from the VDE_BUSY variable. 
     At  1212 , method  1200  judges if cylinder valve deactivation is requested to lower the number of active cylinders. Cylinder valves deactivation may be requested in response to a lower driver demand torque or other driving conditions. If method  1200  judges that cylinder valve deactivation is requested from the present cylinder mode or VDE mode, the answer is yes and method  1200  proceeds to  1214 . Otherwise, the answer is no and method  1200  proceeds to  1240 . 
     At  1240 , method  1200  judges if cylinder valve reactivation is requested to increase the number of active cylinders (e.g., if intake valves of two cylinders are requested to be reactivated in response to an increase in driver demand torque). Cylinder valves may be reactivated to reactivate a cylinder. The cylinder may be reactivated in response to an increase in driver demand torque or another condition. If method  1200  judges that cylinder valve reactivation is requested, the answer is yes and method  1200  proceeds to  1244 . Otherwise, the answer is no and method  1200  proceeds to  1242 . 
     At  1244 , method  1200  authorizes reactivation of deactivated cylinder valves and cylinders. The cylinder valves may be reactivated via the mechanisms shown in  FIGS. 6A and 6B  or other known mechanisms Method  1200  proceeds to exit after authorizing reactivation of deactivated cylinder valves. The valves may be activated according to the method of  FIG. 22 . 
     At  1242 , method  1200  does not authorize activating or deactivating a different number of cylinder valves than those that are presently activated or deactivated. In other words, the number of activated valves and cylinders is maintained at its present value. Method  1200  proceeds to exit after maintaining the present number of activated and deactivated cylinders. 
     At  1214 , method  1200  judges if an amount of time since a cylinder valve reactivation request is greater than the value of variable VDE_BUSY. If so, the answer is yes and method  1200  proceeds to  1216 . Otherwise, the answer is no and method  1200  proceed to  1242 . In this way, cylinder valve deactivation may be delayed until an amount of time between cylinder mode or VDE mode changes is greater than the value of VDE_BUSY which increases when the frequency of cylinder valve deactivation increases and decreases when the frequency of cylinder valve deactivation decreases. 
     At  1216 , method  1200  authorizes deactivation of selected cylinder valves to deactivate selected cylinders. Deactivation of fuel supplied to the cylinders and spark to the cylinders may also be authorized. The valves may be deactivated according to the method of  FIG. 22 . 
     Referring now to  FIG. 13 , an engine operating sequence according to the method of  FIG. 12  is shown. The vertical lines at time T 1300 -T 1314  represent times of interest in the sequence.  FIG. 13  shows six plots and the plots are time aligned and occur at the same time. In this example, deactivating a cylinder means deactivating at least intake valves of the cylinder being deactivated so that the deactivated intake valves remain in closed states during an entire engine cycle. In some examples, exhaust valves of deactivated cylinders are also deactivated so that the exhaust valves remain in a closed state during a cycle of the engine. Spark and fuel are not supplied to deactivated cylinders so that combustion does not occur in deactivated cylinders. Alternatively, cylinder deactivation may include ceasing combustion and fuel injected to a cylinder while valves of the cylinder continue to operate. 
     The first plot from the top of  FIG. 13  is a plot of cylinder deactivation request versus time. Engine cylinders may be deactivated in response to the cylinder deactivation request. The vertical axis represents cylinder deactivation request and the horizontal axis represents time. Time increases from the left side of the figure to the right side of the figure. In this example, the engine is an eight cylinder engine that may operate with four, six, or eight active cylinders. The numbers along the vertical axis identify which cylinders are requested or not requested to be deactivated. For example, when the trace is at the level of eight, no cylinders are requested deactivated. When the trace is at the level of six, two cylinders are requested deactivated. Four cylinders are requested deactivated when the trace is at the level of four. A cylinder deactivation request may be based on driver demand torque or other vehicle conditions. In some examples, only intake valves of a cylinder are deactivated to deactivate a cylinder. In other examples, intake valves and exhaust valves are deactivated to deactivate a cylinder. If a cylinder is deactivated, spark and fuel flow cease to the cylinder. 
     The second plot from the top of  FIG. 13  is a plot of cylinder activation state versus time. The cylinder activation state provides the actual operating state of engine cylinders. The vertical axis represents cylinder activation state and the horizontal axis represents time. The numbers along the vertical axis identify which cylinders are activated. For example, when the trace is at the level of eight, all cylinders are activated. If the trace is at the level of six, six cylinders are activated. Four cylinders are activated when the trace is at the level of four. The horizontal axis represents time and time increases from the left side of the figure to the right side of the figure. 
     The third plot from the top of  FIG. 13  is a plot of the amount of time the engine is in the first cylinder mode, six cylinder operation in this example. The vertical axis represents the amount of time in the first cylinder mode and time in the first cylinder mode increases in the direction of the vertical axis arrow. The horizontal axis represents time and time increases from the left side of the figure to the right side of the figure. 
     The fourth plot from the top of  FIG. 13  is a plot of the amount of time the engine is in the second cylinder mode, four cylinder operation in this example. The vertical axis represents the amount of time in the second cylinder mode and time in the second cylinder mode increases in the direction of the vertical axis arrow. The horizontal axis represents time and time increases from the left side of the figure to the right side of the figure. 
     The fifth plot from the top of  FIG. 13  is a plot of the value of the VDE_BUSY variable for the first cylinder valve deactivation mode, six cylinder operation in this example. The vertical axis represents the value of the VDE_BUSY variable in the first cylinder mode. The value corresponds to an amount of time that has to pass after a request to enter the first cylinder mode is requested before the first cylinder mode may be entered. The horizontal axis represents time and time increases from the left side of the figure to the right side of the figure. 
     The sixth plot from the top of  FIG. 13  is a plot of the value of the VDE_BUSY variable for the second cylinder mode, four cylinder operation in this example. The vertical axis represents the value of the VDE_BUSY variable in the second cylinder mode. The value corresponds to an amount of time that has to pass after a request to enter the second cylinder mode is requested before the second cylinder mode may be entered. The horizontal axis represents time and time increases from the left side of the figure to the right side of the figure. 
     At time T 1300 , the engine is operating with all valves and cylinders active as indicated by the cylinder activation state being a value of eight. The cylinder deactivation request is not requesting to deactivate any valves or cylinders and the amount of time in the first and second cylinder modes is zero. The VDE_BUSY variable for the first cylinder mode, which deactivates cylinders, is zero. The VDE_BUSY variable for the second cylinder mode, which deactivates cylinders, is also zero. 
     At time T 1301 , the cylinder deactivation request changes state to request deactivation of valves of two cylinders so that the eight cylinder engine operates with six active cylinders. The cylinder activation state changes state to indicate that the engine is operating with six active cylinders and with valves of two cylinders deactivated. Time begins to accumulate in the first cylinder mode because the engine is in the first cylinder mode (e.g., operating with six active cylinders). No time accumulates in the second cylinder mode because the engine is not operating in the second cylinder mode (e.g., operating with four active cylinders). The variables VDE_BUSY for the first cylinder mode and VDE_BUSY for the second cylinder mode are zero since the engine has not exited the first or second cylinder modes. 
     At time T 1302 , the cylinder deactivation request change state to request deactivation of no cylinder valves so that the engine operates as an eight cylinder engine. The cylinder activation state changes state to indicate that the engine is operating with eight active cylinders and with no deactivated valves. Accumulation of time in the first cylinder mode ceases because the engine is operating all cylinder valves and as an eight cylinder engine. No time accumulates in the second cylinder mode because the engine is not operating in the second cylinder mode. The value of VDE_BUSY for the first cylinder mode increases based on the time duration the engine was in the first cylinder mode. 
     At time T 1303 , the cylinder deactivation request again changes state to request deactivation of valves of two cylinders so that the eight cylinder engine operates with six active cylinders. The cylinder activation state does not change state because the value of VDE_BUSY for the first cylinder mode is greater than the variable PAYBACK_TIME (not shown). The value of VDE_BUSY for the first cylinder mode decreases as a predetermined amount of time is subtracted from VDE_BUSY first cylinder mode each time the method is executed. No time accumulates in the second cylinder mode because the engine is not operating in the second cylinder mode (e.g., operating with four active cylinders). VDE_BUSY for the second cylinder mode is zero since the engine has not exited the second cylinder mode. 
     At time T 1304 , the value of VDE_BUSY for the first cylinder mode is equal to or less than the value of the variable PAYBACK_TIME so cylinder valves are deactivated to provide six cylinder engine operation as indicated by the cylinder activation state transitioning to the level that indicates six cylinder engine operation. The amount of time in the first cylinder mode begins to increase. The amount of time in the second cylinder mode remains at zero. The value of VDE_BUSY for the first cylinder valve deactivation mode continues to decrease and the value of VDE_BUSY for the second cylinder valve deactivation mode remains at zero. 
     At time T 1305 , the cylinder deactivation request transitions back to the value of eight. The cylinder activation state also transitions back to a value of eight based on the cylinder deactivation request. The amount of time in the first cylinder mode is small so the value of VDE_BUSY for the first cylinder mode is increased by a large amount. The value of VDE_BUSY for the second cylinder mode is zero because the engine was not in the second cylinder mode. Shortly thereafter, the cylinder deactivation request transitions to a value of six to request deactivation of valves in two engine cylinders so that the engine operates as a six cylinder engine combusting air fuel mixtures in six of eight cylinders. However, the engine is not switched into six cylinder operation as indicated by the cylinder activation state remaining at a value of eight. The engine does not switch into six cylinder mode and deactivate valves of two cylinders because the value of VDE_BUSY for the first cylinder mode is greater than the value of the variable PAYBACK_TIME (not shown). 
     At time T 1306 , the engine transitions to six cylinder mode where cylinder valves in two engine cylinders are deactivated to deactivate two cylinders. Fuel and spark are not provided to the two deactivated cylinders. The cylinder activation state transitions to a value of six to indicate that the engine is operating in six cylinder mode with cylinder valves deactivated in two cylinders. The amount of time in the first cylinder mode begins to increase. The amount of time in the second cylinder mode remains at zero. The value of VDE_BUSY for the first cylinder mode continues to decrease and the value of VDE_BUSY for the second cylinder mode remains at zero. 
     At time T 1307 , the cylinder deactivation request transitions to eight to request eight active cylinders. The amount of time the engine operated in the first cylinder mode is long so the value of VDE_BUSY for the first mode is revised to a small value. The cylinder activation state is transitioned to a value of eight to indicate that the engine has activated all eight cylinders and valves. The amount of time in the second cylinder mode is zero and the value of VDE_BUSY for the second cylinder mode is zero. 
     At time T 1308 , the cylinder deactivation request transitions to a value of six in response to a reduced driver demand torque (not shown). At nearly the same time, the cylinder activation state also transitions to a value of six based on the cylinder deactivation request. The amount of time in the first cylinder mode begins to increase and the amount of time in the second cylinder mode remains at zero. The values of VDE_BUSY for the first and second valve deactivation modes are zero. 
     At time T 1309 , the cylinder deactivation request transitions to a value of four in response to driver demand torque (not shown). The cylinder activation state also transitions to a value of four in response to the cylinder deactivation request value. The amount of time in the first cylinder mode is transitioned to zero and the VDE_BUSY value for the first cylinder mode is made zero. The amount of time in the second cylinder mode begins to increase and the VDE_BUSY value for the second cylinder valve deactivation mode remains at a value of zero. 
     At time T 1310 , the cylinder valve deactivation request transitions back to a value of six in response to the driver demand torque increasing (not shown). The cylinder activation state transitions back to a value of six in response to the value of the cylinder deactivation request. The value of VDE_BUSY for the second cylinder valve deactivation mode is increased in response to the short amount of time the engine is operated in four cylinder mode. The amount of time in the first cylinder mode begins to increase and the amount of time in the second cylinder mode is made zero. 
     At time T 1311 , the cylinder deactivation request transitions back to a value of four in response to the driver demand torque decreasing (not shown). The cylinder activation state remains at a value of six because the value of VDE_BUSY for the second cylinder mode is greater than the value of the variable PAYBACK_TIME (not shown). The amount of time in the first cylinder mode continues to increase and the amount of time in the second cylinder mode remains at zero. The value of VDE_BUSY for the first cylinder valve deactivation mode remains at zero. 
     At time T 1312 , the cylinder deactivation request transitions back to a value of six in response to the driver demand torque increasing (not shown). The cylinder activation state is at a value of six based on the value of the cylinder deactivation request. The amount of time in the first cylinder mode continues to increase and the amount of time in the second cylinder mode is zero. The value of VDE_BUSY for the second cylinder mode continues to decrease since the engine was not transitioned out of the second cylinder mode. 
     At time T 1313 , the cylinder deactivation request transitions to a value of four in response to the driver demand torque decreasing (not shown). The cylinder activation state remains at a value of six because the value of VDE_BUSY for the second cylinder mode is greater than the value of the variable PAYBACK_TIME (not shown). Thus, valves of two cylinders are deactivated even though the cylinder deactivation request is at a value of four. The amount of time in the first cylinder mode continues to increase and the amount of time in the second cylinder mode remains at zero. The value of VDE_BUSY for the first cylinder mode remains at zero. 
     At time T 1314 , the cylinder deactivation request remains at a value of four and the cylinder activation state transitions to a value of four in response to the value of PAYBACK_TIME (not shown). Thus, valves of four cylinders are deactivated and four cylinders are activated. The amount of time in the first cylinder mode is transitioned to zero and the VDE_BUSY value for the first cylinder mode is made zero. The amount of time in the second cylinder mode begins to increase and the VDE_BUSY value for the second cylinder mode continues to decrease. 
     At time T 1315 , the cylinder deactivation request transitions to a value of eight to request activation of all cylinder valves and cylinders. The cylinder activation state is transitioned to a value of eight to indicate that all cylinder valves and cylinders are activated. The amount of time in the second cylinder mode is long so the value of VDE_BUSY for the second valve mode is made small, thereby permitting a quick transition into four cylinder mode where cylinder valves of four cylinders are deactivated. 
     Thus, it may be observed that entry into various cylinder modes may be prevented based on the amount of time in a cylinder mode relative to a payback time. Further, the cylinder modes are not locked out in response to cylinder mode shifting busyness. Instead, entry into the various cylinder modes may be delayed for varying amounts of time to reduce a driver&#39;s perception of cylinder mode switching busyness. 
     Referring now to  FIG. 14 , a method for evaluating engine brake torque in available cylinder modes as a basis for selectively allowing cylinder deactivation is shown. The method of  FIG. 14  may be included in the system described in  FIGS. 1A-6C . The method of  FIG. 14  may be included as executable instructions stored in non-transitory memory. The method of  FIG. 14  may perform in cooperation with system hardware and other methods described herein to transform an operating state of an engine or its components. 
     At  1402 , method  1400  determines a desired engine torque and present engine speed. Engine speed may be determined via an engine position or speed sensor. An amount of time it takes for the engine to travel between two positions is the engine speed. The desired engine torque may be determined from a driver demand torque. In one example, the driver demand torque is based on accelerator pedal position and vehicle speed. Accelerator pedal position and vehicle speed index a table of empirically determined driver demand torque values. The driver demand torque value corresponds to a desired torque at a position along the driveline. The position along the driveline may be the engine crankshaft, the transmission input shaft, transmission output shaft, or vehicle wheel. If the driver demand torque is an engine torque, output from the table is the desired or demanded engine torque. Torques at other locations along the driveline may be determined via adjusting a desired torque at one location based on gear ratios, torque multiplication devices, losses, and torque capacities of clutches. 
     For example, if driver demand torque is a wheel torque, engine torque may be determined by multiplying the driver demand torque (or the desired wheel torque) by the gear ratios between the wheel and the engine. Further, if the driveline includes a torque converter, the desired wheel torque may be divided by the torque converter torque multiplication factor to determine engine torque. Torque transferred via clutches may be estimated as a multiplier. For example, if a clutch is not slipping torque input to the clutch equals torque output from the clutch and the multiplier value is one. Torque input to the clutch multiplied by one yields clutch output torque. If the clutch is slipping, the multiplier is a value from 0 to a number less than one. The multiplier value may be based on the clutch&#39;s torque capacity. Method  1400  proceeds to  1404 . 
     At  1404 , method  1400  determines cylinder modes that may provide the desired engine torque. In one example, an engine torque table may be provided that describes maximum engine torque output as a function of cylinder mode and engine speed. The desired engine torque is compared to engine cylinder valve timing and barometric pressure compensated outputs from the engine torque table indexed by the cylinder mode at the present engine speed, barometric pressure, and cylinder valve timing (e.g., intake valve closing timing). If the engine torque table outputs a torque value that is greater than the desired engine torque plus an offset torque, the cylinder mode corresponding to the torque output by the table may be determined to be a cylinder mode that provides the desired engine torque. Values stored in the engine torque table may be empirically determined and stored to controller memory. 
     On example of an engine brake torque table is shown in  FIG. 1 . It is an engine torque table for a four cylinder engine. The engine torque table may include torque output values for three cylinder modes; a mode with two active cylinders, a mode with three active cylinders, and a mode with four active cylinders. The engine torque table may also include a plurality of engine speeds. Torque values between the engine speeds may be interpolated. 
                                 TABLE 1                          Engine speed                                             500   1000   2000   3000   4000                                                             Active   2   39   48   52   49   43           cylinders   3   58   74   79   76   65               4   77   96   104   100   88                       Table 1.            
Thus, table 1 includes rows of active cylinder modes and columns of engine speed. Table 1 outputs torque values in units of N-m in this example. The engine brake torque values output from the brake torque table may be adjusted by functions based on spark timing from minimum spark for best torque (MBT), intake valve closing time from a nominal intake valve closing time, engine air-fuel ratio, and engine temperature. The functions output empirically determined multipliers that modify the engine brake torque value output from the engine brake torque table. The desired engine brake torque is compared to the modified value output from the engine brake torque table. Note that a desired wheel torque may be converted to a desired engine torque via multiplying the desired wheel torque by the gear ratio between the wheels and the engine. Further, determining engine torque may include modifying the wheel torque according to the torque multiplication of the transmission torque converter. Additionally, or alternatively, cylinder modes that include different firing orders or active cylinders in an engine cycle may also be a basis for indexing and storing values in an engine brake torque table. Method  1400  proceeds to  1406 .
 
     At  1406 , method  1400  allows cylinder modes that provide the desired engine torque to be allowed. Allowed cylinder modes may be activated at  716  of  FIG. 7 . 
     An example using table 1: table 1 is indexed by engine speed and cylinder mode. The cylinder mode begins at a minimum value, two in this example, and it incremented until it reaches the maximum cylinder mode. For example, if the engine is operating at 1000 RPM and the desired engine torque is 54 N-m, table 1 outputs a value of 48 N-m corresponding to 1000 RPM and cylinder mode two (e.g., two active cylinders), 74 N-m corresponding to 1000 RPM and cylinder mode three (e.g., three active cylinders), and 96 N-m corresponding to 1000 RPM and cylinder mode four (e.g., four active cylinders). The cylinder mode with two active cylinders at 1000 RPM is not allowed because two active cylinders lack capacity to provide the desired 74 N-m of torque. Cylinder modes with three and four cylinders are allowed. In some examples, the desired engine torque plus a predetermined offset is compared to values output from the table. If the desired engine torque plus the predetermined offset is greater than an output from the table, the cylinder mode corresponding to the table output is not allowed. Allowed and not allowed cylinder modes may be indicated by values of variables stored in memory. For example, if three cylinder mode is allowed at 1000 RPM, a variable in memory corresponding to three cylinder mode at 1000 RPM may be populated with a value of one. If cylinder mode three is not allowed at 500 RPM, a variable in memory corresponding to cylinder mode three at 500 RPM may be populated with a value of zero. Method  1400  proceeds to exit. 
     Thus, engine cylinder modes and engine brake torque available in the cylinder modes may be a basis for determining which cylinder mode the engine operates with. Further, cylinder modes with lower fuel consumption may be given selection priority so that fuel may be conserved. 
     Referring now to  FIG. 15 , a method for evaluating engine fuel consumption in available cylinder modes as a basis for selectively allowing cylinder deactivation is show. The method of  FIG. 15  may be included in the system described in  FIGS. 1A-6C . The method of  FIG. 15  may be included as executable instructions stored in non-transitory memory. The method of  FIG. 15  may perform in cooperation with system hardware and other methods described herein to transform an operating state of an engine or its components. 
     At  1502 , method  1500  determines a desired engine torque and present engine speed. Engine speed may be determined via an engine position or speed sensor. Method  1500  proceeds to  1504 . 
     At  1504 , method  1500  determines cylinder modes that may provide the desired engine torque. In one example, cylinder modes that may provide the desired engine torque are determined as described in  FIG. 14 . 
     At  1506 , method  1500  estimates fuel consumption in cylinder modes that are allowed. The allowed cylinder modes are from  1406  of  FIG. 14 . In one example, a brake specific fuel table or function indexed by cylinder modes from the allowed cylinder modes from  FIG. 14 , engine speed, and desired engine torque outputs a brake specific fuel consumption value. Values stored in the brake specific fuel table may be empirically determined and stored to controller memory. The brake specific fuel consumption value may be adjusted by functions based on spark timing from minimum spark for best torque (MBT), intake valve closing time from a nominal intake valve closing time, engine air-fuel ratio, and engine temperature. The functions output empirically determined multipliers that modify the brake specific fuel consumption value output from the table. Brake specific fuel values for each allowed cylinder mode at the present engine speed are output from the brake specific fuel table. For example, from the example described at  1406 , the actual number of active cylinders is three and four since three and four cylinder modes provide the desired engine torque. Method  1500  proceeds to  1508 . 
     At  1508 , method  1500  compares fuel consumption for the allowed cylinder modes that can provide the requested torque. In one example, the present engine fuel consumption, which may be determined by the present engine fuel flow rate, is compared to values output from the brake specific fuel table for allowed cylinder modes. The comparison may be performed by subtracting values output from the brake specific fuel table from the present engine fuel consumption rate. Alternatively, the comparison may be based on dividing the present engine fuel consumption value by the values output from the brake specific fuel table. Cylinder modes that provide greater than a threshold percentage improvement in engine fuel economy over the present cylinder mode are allowed. 
     Thus, cylinder modes and fuel consumption in the cylinder modes may be a basis for determining which cylinder mode the engine operates with. Further, cylinder modes with lower fuel consumption may be given selection priority so that fuel may be conserved. 
     Referring now to  FIG. 16 , a method for evaluating a rate of cam phasing for cam torque actuated cam phase adjustments is shown. The method of  FIG. 16  may be included in the system described in  FIGS. 1A-6C . The method of  FIG. 16  may be included as executable instructions stored in non-transitory memory. The method of  FIG. 16  may perform in cooperation with system hardware and other methods described herein to transform an operating state of an engine or its components. Method  1600  may be performed for each engine camshaft. 
     At  1602 , method  1600  determines engine conditions. Engine conditions may include but are not limited to an actual total number of cylinder valves that are deactivated during an engine cycle, engine speed, driver demand torque, vehicle speed, engine temperature, and ambient temperature. Method  1600  proceeds to  1604  after operating conditions are determined. 
     At  1604 , method  1600  judges if one or more cylinder valves is deactivated. Method  1600  may judge that one or more cylinder is deactivated based on a value of a bit stored in memory, output of a sensor that measures valve operator position, cylinder pressure sensors, or other sensors. If method  1600  judges that one or more cylinder valves is deactivated, the answer is yes and method  1600  proceeds to  1606 . Otherwise, the answer is no and method  1600  proceeds to  1634 . 
     At  1606 , method  1600  judges if a camshaft position adjustment relative to crankshaft position is desired. For example, method  1600  judges if it is desirable to advance camshaft timing 5 degrees relative to crankshaft timing so that intake or exhaust valves open 5 crankshaft degrees sooner after camshaft position is adjusted. The camshaft position may be adjusted in response to driver demand torque and engine speed. If driver demand torque is increasing rapidly and engine speed is increasing rapidly, it may be desirable to adjust camshaft position relative to crankshaft position at a higher rate of speed so that the engine provides a desired amount of torque and engine emissions. In one example, method  1600  determines if a camshaft position adjustment is desired based on a current camshaft position relative to crankshaft position and a change in driver demand torque and engine speed. If method  1600  judges that a camshaft position adjustment is desired, the answer is yes and method  1600  proceeds to  1608 . Otherwise, the answer is no and method  1600  proceeds to  1634 . In some examples,  1606  may be omitted and method  1600  may simply proceed to  1608 . 
     At  1608 , method  1600  determines a desired rate of camshaft position change relative to crankshaft position. In one example, method  1600  determines a desired rate of camshaft position change based on a rate of change in driver demand torque. If the rate of change of driver demand torque is low, the rate of change of camshaft position relative to crankshaft position is low. If the rate of change of driver demand torque is high, the rate of camshaft position change relative to crankshaft position is high. For example, the camshaft may be advanced at 0.5 crankshaft degrees per second when a change in driver demand torque is low (e.g., 5 N-m/second). However, if the change in driver demand torque is high (e.g., 200 N-m/second), the camshaft may be advanced at 5 crankshaft degrees per second In one example, the desired rate of camshaft position change relative to crankshaft position is empirically determined and stored to memory in a table or function. The table or function is indexed based on a rate of change in driver demand torque, the table or function outputs a desired rate of camshaft position change relative to crankshaft position. Method  1600  proceeds to  1610  after the desired rate of camshaft position change is determined. 
     At  1610 , method  1600  judges if an actual total number of active cylinder valves (e.g., valves that open and close during an engine cycle) presently operating is sufficient to move the camshaft relative to the crankshaft at the desired rate. In one example, a table or function describes camshaft rate of position change relative to the crankshaft position based on an actual total number of active cylinder valves. The table is indexed via the actual total number of active valves and it outputs a rate of camshaft position change relative to crankshaft position. Values in the table or function are empirically determined and stored in memory. Output from the table or function is compared to the value determined at  1608 . If the camshaft rate of position change from  1610  is greater than the camshaft rate of position change from  1608 , the answer is yes and method  1600  proceeds to  1634 . Otherwise, the answer is no and method  1600  proceeds to  1612 . 
     At  1612 , method  1600  judges if the camshaft operates both intake and exhaust valves. In one example, a bit in memory identifies the camshaft as operating only intake valves if a value of the bit is zero. If the value of the bit is one, the camshaft operates both intake and exhaust valves. If method  1600  judges that the camshaft operates intake and exhaust valves, the answer is yes and method  1600  proceeds to  1630 . Otherwise, the answer is no and method  1600  proceeds to  1614 . 
     At  1614 , method  1600  judges if the camshaft is an intake camshaft. Method  1600  may judge if the camshaft is an intake camshaft based on a value of a bit stored in memory. The bit may be programed at time of manufacture. If method  1600  judges that the camshaft is an intake camshaft, the answer is yes and method  1600  proceeds to  1616 . Otherwise, the answer is no and method  1600  proceeds to  1620 . 
     At  1620 , method  1600  authorizes activating one or more deactivated exhaust valves. In one example, the desired rate of exhaust camshaft position change relative to crankshaft position determined at  1608  is used to index a table or function of empirically determined values that describe an actual total number of valves that have to operate to provide the desired rate of exhaust camshaft position adjustment relative to crankshaft position. Method  1600  requests or authorizes operation of the actual total number of exhaust valves output from the table or function. The exhaust valves may be activated with or without activating cylinders that include the exhaust valves being activated. If the driver demand torque is increasing, the cylinders with exhaust valves being activated may be activated to increase engine torque while increasing the camshaft position change. If the driver demand torque is decreasing, the cylinders with exhaust valves being activated may not be activated so that fuel consumption may be reduced. Method  1600  proceeds to  1634 . 
     At  1634 , method  1600  moves the camshaft and operates valves for operating conditions after the camshaft is moved. The camshaft may be moved while valves are being activated to move the camshaft to a desired position as soon as possible. After the camshaft reaches its desired position relative to the crankshaft position, cylinder valves may be deactivated based on vehicle conditions other than the desired rate of camshaft position change. In this way, valves may be reactivated to improve a rate that a camshaft position moves relative to a crankshaft position. The engine cylinders may also be reactivated when the cylinder valves are reactivated. Method  1600  proceeds to exit after the camshaft begins to move to its desired new position based on driver demand torque and engine speed. 
     At  1616 , method  1600  authorizes activating one or more deactivated intake valves. In one example, the desired rate of intake camshaft position change relative to crankshaft position determined at  1608  is used to index a table or function of empirically determined values that describe an actual total number of valves that have to operate to provide the desired rate of intake camshaft position adjustment relative to crankshaft position. Method  1600  requests or authorizes operation of the actual total number of intake valves output from the table or function. The cylinders that include the intake valves that are being activated may be activated or they may not combust air and fuel during engine cycles when the intake valves are being operated. In one example, the cylinders with intake valves being activated combusts air and fuel during engine cycles in response to an increase in driver demand torque. The cylinders with intake valves being activated may not combust air and fuel during engine cycles in response to a decrease in driver demand torque. Deactivated intake valves may be activated as described at  FIG. 22 . 
     In addition, method  1600  may increase an amount of boost provided to the engine so that the additional boost may blow exhaust gases from the cylinder before the exhaust valve of the cylinder being reactivated is closed. By clearing exhaust gases from the cylinder, combustion stability may improve and the cylinder may provide additional power. Additionally, an amount of overlap (e.g., open time) between the cylinder&#39;s intake valves and exhaust valves may be increased to further allow pressurized air from the intake manifold to clear out the cylinder being activated. Method  1600  proceeds to  1634  after intake valves are activated. 
     At  1630 , method  1600  judges if engine noise vibration and harshness (NVH) are less than threshold levels if one or more cylinders are reactivated and combustion occurs in the reactivated cylinders. In one example, method  1600  judges if reactivating one or more cylinders including combusting air and fuel in the reactivated cylinders will produce NVH greater than is desired based on output of a table or function that describes engine and/or powertrain NVH. The table is indexed via engine speed, driver demand torque, and cylinder mode being activated (e.g., four or six cylinder mode). The table outputs a numerical value that is empirically determined, via a microphone or accelerometer for example. If the output value is less than a threshold value, the answer is yes and method  1600  proceeds to  1632 . Otherwise, the answer is no and method  1600  proceeds to  1640 . 
     At  1632 , method  1600  authorizes activating one or more cylinder via activating the cylinder&#39;s valves and supplying fuel, air, and spark to the cylinder. The cylinder begins combusting air and fuel when it is reactivated. Thus, if reactivating one or more cylinders to increase camshaft rate of position change produces little objectionable NVH, the cylinder is reactivated via reactivating the cylinder&#39;s valves and beginning combustion in the reactivated cylinder. Method  1600  proceeds to  1634 . 
     At  1640 , method  1600  authorizes activating one or more valves of a deactivated cylinder that is not combusting air and fuel. If the cylinder includes deactivated intake and exhaust valves, only the cylinders exhaust valves may be activated to improve the rate of camshaft position adjustment relative to crankshaft position. By reactivating only exhaust valves of the cylinder, cam torque may be increased to improve the camshaft position adjustment relative to crankshaft position without flowing air through the cylinder. Stopping air flow through the cylinder may help to keep catalyst temperature elevated and maintain a desired amount of oxygen in the catalyst. If both intake and exhaust valves of the cylinder are reactivated, air may flow through the cylinder after the intake and exhaust valves are activated. Spark and fuel are not supplied to the cylinders with reactivated valves so that NVH may not degrade. Method  1600  proceeds to  1642 . 
     At  1642 , method  1600  increases an amount of fuel delivered to an active cylinder combusting air and fuel to richen the mixture combusted by the active cylinder if air is flowing through the cylinder with one or more valves authorized to be activated at  1640 . By richening the mixture of an active cylinder combusting air and fuel while air flows through a cylinder, it may be possible to maintain desired levels of hydrocarbons and oxygen in a catalyst so that the catalyst may convert exhaust gases efficiently. For example, if cylinder number eight of an eight cylinder engine has its intake and exhaust valves reactivated while cylinder number eight is not combusting air and fuel, the air-fuel ratio of cylinder number one that is combusting air and fuel may be richened to improve or maintain catalyst efficiency. Method  1600  proceeds to  1634  after enriching at least one cylinder&#39;s air-fuel ratio. 
     Referring now to  FIG. 17 , a sequence for operating an engine according to the method of  FIG. 16  is shown. The vertical lines at time T 1700 -T 1704  represent times of interest in the sequence.  FIG. 17  shows six plots and the plots are time aligned and occur at the same time. In this example, the engine is a four cylinder engine with a firing order of 1-3-4-2. Cylinders  2  and  3  have deactivating valve operators for deactivating cylinders  3  and  4 . Valves of cylinders  1  and  4  always remain active. 
     The first plot from the top of  FIG. 17  is a plot of a camshaft movement request versus time. A camshaft movement request is a request to change a position of a camshaft relative to a position of a crankshaft. For example, if a camshaft has a lobe that begins to open an intake valve of cylinder number one of an engine 370 crankshaft degrees before top-dead-center compression stroke (e.g., position of crankshaft zero degrees), the position of the camshaft may be moved relative to the crankshaft so that the camshaft lobe begins to open the intake valve of cylinder number one of the engine at 380 crankshaft degrees before top-dead-center compression stroke. Thus, in this example, the relative position of the camshaft is advanced 10 crankshaft degrees relative to the crankshaft position. 
     The vertical axis represents the camshaft move request. The cam move request trace is at a higher level and asserted when it is desired to move the engine camshaft relative to the engine crankshaft. The cam move request trace is at a lower level and not asserted when it is not desired to move the engine camshaft relative to the engine crankshaft. The horizontal axis represents time and time increases from the left side of the figure to the right side of the figure. 
     The second plot from the top of  FIG. 17  is a plot of camshaft position versus time. The vertical axis represents camshaft position and the camshaft is more advanced in the direction of the vertical axis arrow. The horizontal axis represents time and time increases from the left side of the figure to the right side of the figure. 
     The third plot from the top of  FIG. 17  is a plot of deactivating cylinder intake valve state. In this example, the deactivating cylinder may be cylinder number two or cylinder number three. The deactivating cylinder intake valve state indicates whether or not the intake valve of the deactivating cylinder is activated (e.g., opening and closing during an engine cycle) or deactivated (e.g., held closed during an entire engine cycle). The vertical axis represents deactivating cylinder intake valve state. The deactivating cylinder intake valve is active when the trace is at a higher level near the vertical axis arrow. The deactivating cylinder intake valve is deactivated when the trace is at a lower level near the horizontal axis. The horizontal axis represents time and time increases from the left side of the figure to the right side of the figure. 
     The fourth plot from the top of  FIG. 17  is a plot of deactivating cylinder exhaust valve state. In this example, the deactivating cylinder may be cylinder number two or cylinder number three. The deactivating cylinder exhaust valve state indicates whether or not the exhaust valve of the deactivating cylinder is activated (e.g., opening and closing during an engine cycle) or deactivated (e.g., held closed during an engine cycle). The vertical axis represents deactivating cylinder exhaust valve state. The deactivating cylinder exhaust valve is active when the trace is at a higher level near the vertical axis arrow. The deactivating cylinder exhaust valve is deactivated when the trace is at a lower level near the horizontal axis. The horizontal axis represents time and time increases from the left side of the figure to the right side of the figure. 
     The fifth plot from the top of  FIG. 17  is a plot of deactivating cylinder fuel flow state. In this example, the deactivating cylinder may be cylinder number two or cylinder number three. The deactivating cylinder fuel flow state indicates whether or not the fuel is flowing to the deactivating cylinder. The vertical axis represents deactivating cylinder fuel flow state. Fuel is flowing to the deactivating cylinder when the deactivating cylinder fuel flow trace is at a higher level near the vertical axis arrow. Fuel is not flowing to the deactivating cylinder when the deactivating cylinder fuel flow trace is at a lower level near the horizontal axis. The horizontal axis represents time and time increases from the left side of the figure to the right side of the figure. 
     The sixth plot from the top of  FIG. 17  is a plot of active cylinder fuel air-fuel ratio. In this example, the active cylinder may be cylinder number  1  or cylinder number  4 . The vertical axis represents active cylinder air-fuel ratio and the air-fuel ration increases (e.g., become leaner) in the direction of the vertical axis arrow. The horizontal axis represents time and time increases from the left side of the figure to the right side of the figure. Horizontal line  1702  represents a stoichiometric air-fuel ratio. 
     At time T 1700 , there is not a camshaft move request and the camshaft is relatively retarded. The deactivating cylinder intake valve state indicates that the deactivating cylinder intake valve is deactivated (e.g., not opening during a cycle of the engine). The deactivating cylinder exhaust valve state indicates that the deactivating cylinder exhaust valve is deactivated (e.g., not opening during a cycle of the engine). The active cylinder is operating at a stoichiometric air-fuel ratio and no fuel flows to the deactivating cylinder as indicated by the deactivating cylinder fuel flow state being at a low level. 
     At time T 1701 , the camshaft move request is asserted requesting a camshaft position change relative to a position of the engine crankshaft. The request may be initiated via an increase in a driver demand torque or a change in another operating condition. The rate of change in position of the engine camshaft relative to the position of the engine crankshaft (not shown) is greater than that which may be accomplished with the deactivating cylinder intake and exhaust valves deactivated since operating fewer valves provides less torque to actuate camshaft motion. Therefore, the deactivating cylinder&#39;s intake and exhaust valves are reactivated as indicated by the deactivating cylinder intake valve state and exhaust valve state transitioning to higher levels to indicate the intake and exhaust valves of the deactivating cylinder are reactivated. Additionally, fuel flows to the deactivating cylinder and combustion begins in the deactivating cylinder (not shown). The camshaft position is advanced while the deactivating cylinder intake and exhaust valves are activated. The air-fuel ratio of the active cylinders is stoichiometric. 
     At time T 1702 , the camshaft move request transitions to a not asserted state. The camshaft move request may transition to not asserted when the camshaft reaches its destination. Further, fuel stops flowing to the deactivating cylinder and combustion stops in the deactivating cylinder (not shown). The camshaft position reaches a middle advanced position and is maintained at its position. The air-fuel ratios of the active cylinders remain stoichiometric. 
     At time T 1703 , the camshaft move request is asserted again requesting a camshaft position change relative to a position of the engine crankshaft. The request may be initiated via an increase in a driver demand torque or a change in another operating condition. The rate of change in position of the engine camshaft relative to the position of the engine crankshaft (not shown) is greater than that which may be accomplished with the deactivating cylinder intake and exhaust valves deactivated since operating fewer valves provides less torque to actuate camshaft motion. As a result, the deactivating cylinder&#39;s intake and exhaust valves are reactivated as indicated by the deactivating cylinder intake valve state and exhaust valve state transitioning to higher levels to indicate the intake and exhaust valves of the deactivating cylinder are reactivated. Fuel flow to the deactivating cylinders remains stopped. In this example, combustion is not reinitiated in the deactivating cylinders because reactivating the deactivating cylinders is expected to produce NVH levels greater than is desired. The camshaft position is advanced while the deactivating cylinder intake and exhaust valves are activated. The air-fuel ratio of the active cylinders is enrichened so that when the richened exhaust from the activated cylinders meets with oxygen from the deactivating cylinders, a stoichiometric exhaust gases are provided to the catalyst. 
     At time T 1704 , the camshaft move request transitions to a not asserted state. The camshaft move request may transition to not asserted when the camshaft reaches its destination. Further, the deactivating cylinder&#39;s intake and exhaust valves are deactivated as indicated by the deactivating cylinder intake and exhaust valve states. The camshaft position reaches a fully advanced position and is maintained at its position. The air-fuel ratios of the active cylinders transition back to a stoichiometric air-fuel ratio by leaning the air-fuel mixtures of the deactivating cylinders. 
     In this way, cylinder intake and exhaust valves that have been deactivated may be reactivated to provide more rapid position adjustments to the engine camshaft. Further, stoichiometric exhaust gases may be provided to a catalyst to maintain catalyst efficiency whether air or exhaust gases flow from deactivating cylinders. 
     Referring now to  FIG. 18 , a method for judging whether or not to shift transmission gears when evaluating cylinder mode changes is shown. The method of  FIG. 18  may be included in the system described in  FIGS. 1A-6C . The method of  FIG. 18  may be included as executable instructions stored in non-transitory memory. The method of  FIG. 18  may perform in cooperation with system hardware and other methods described herein to transform an operating state of an engine or its components. 
     At  1802 , method  1800  determines a desired wheel torque. In one example, desired wheel torque is determined based on accelerator pedal position and vehicle speed. For example, accelerator pedal position and vehicle speed index a table that outputs desired wheel torque. Values in the table may be empirically determined and stored to controller memory. In other examples, accelerator pedal position and vehicle speed may index a table that outputs desired engine brake torque or torque at another location of the driveline (e.g., transmission input shaft). The output from the table is multiplied by gear ratios between the torque location (e.g., engine), torque converter multiplication, and driveline torque losses to estimate desired wheel torque. Method  1800  proceeds to  1804 . 
     At  1804 , method  1800  determines the presently selected transmission gear. Method  1800  may determine the presently selected transmission gear via a value of a location in controller memory. For example, a variable in memory may range from a value of 1-10, which indicates the presently selected gear ratio. Method  1800  proceeds to  1806 . 
     At  1806 , method  1800  estimates engine fuel consumption in cylinder modes that may provide the desired wheel torque the present transmission gear. Method  1800  determined engine brake specific fuel consumption in the present transmission gear according to the method of  FIG. 15 . Method  1800  proceeds to  1808 . 
     At  1808 , method  1800  estimates engine fuel consumption in cylinder modes that may provide the desired wheel torque the next higher transmission gear. For example, if the transmission is presently in 3 rd  gear, engine fuel consumption to provide equivalent wheel torque with the transmission in 4 th  gear is determined. In one example, method  1800  determines engine brake specific fuel consumption in the next higher transmission gear as follows: the present vehicle speed is divided by the gear ratio between engine and the wheels including the next higher transmission gear to estimate the engine speed in the next higher transmission gear. The present wheel torque is divided by the gear ratio between the engine and the wheels to estimate engine torque for providing equivalent wheel torque in the next higher transmission gear. The gear ratio between the engine and the wheels may also be compensated for the torque converter if one is present. Method  1800  determines cylinder modes that may provide the desired wheel torque in the next higher transmission gear according to the method of  FIG. 14  using the estimate of engine torque in the next higher gear that provides equivalent wheel torque to the present wheel torque. Note that the present wheel torque may be the desired wheel torque. The estimated engine fuel consumption is then determined as described in the description of the method of  FIG. 15 . Method  1800  proceeds to  1810 . 
     At  1810 , method  1800  estimates engine fuel consumption in cylinder modes that may provide the desired wheel torque the next lower transmission gear. For example, if the transmission is presently in 3 rd  gear, engine fuel consumption to provide equivalent wheel torque with the transmission in 2nd gear is determined. In one example, method  1800  determines engine brake specific fuel consumption in the next lower transmission gear as follows: the present vehicle speed is divided by the gear ratio between engine and the wheels including the next lower transmission gear to estimate the engine speed in the next higher transmission gear. The present wheel torque is divided by the gear ratio between the engine and the wheels to estimate engine torque for providing equivalent wheel torque in the next lower transmission gear. The gear ratio between the engine and the wheels may also be compensated for the torque converter if one is present. Method  1800  determines cylinder modes that may provide the desired wheel torque in the next lower transmission gear according to the method of  FIG. 14  using the estimate of engine torque in the next lower gear that provides equivalent wheel torque to the present wheel torque. Note that the present wheel torque may be the desired wheel torque. The estimated engine fuel consumption is then determined as described in the description of the method of  FIG. 15 . Method  1800  proceeds to  1812 . 
     In some examples, method  1800  estimates engine fuel consumption in cylinder modes that may provide the desired wheel torque for all transmission gears. For example, if the transmission is presently in 3 rd  gear, and the transmission includes five forward gears, engine fuel consumption to provide equivalent wheel torque with the transmission in gears  1 ,  2 ,  4 , and  5  is determined. In this way, it may be possible to select whichever gear provides the most improvement in vehicle fuel economy. 
     At  1812 , method  1800  allows activation of transmission gears and cylinder modes that provide greater than a threshold percentage of decrease in engine fuel consumption as compared to present cylinder mode and transmission gear. In one example, brake specific engine fuel consumption in engine cylinder modes that provide the desired engine torque or wheel torque in the next higher transmission gear are divided by the brake specific engine fuel consumption in the present cylinder mode and present transmission gear. If the result is greater than a threshold, the engine cylinder modes that provide the desired engine torque or wheel torque in the next higher transmission gear are allowed. Likewise, engine fuel consumption in engine cylinder modes that provide the desired engine torque or wheel torque in the next lower transmission gear are compared to engine fuel consumption in the present cylinder mode and present transmission gear. If the result is greater than a threshold, the engine cylinder modes that provide the desired engine torque or wheel torque in the next lower transmission gear are allowed. Additionally, method  1800  may require that an expected noise level and an expected vibration level in a new gear (e.g., a higher or lower gear than the present transmission gear) are less than threshold values of noise and vibration. Noise and vibration levels may be assessed as described at  FIG. 22 . Further, if an engine knock sensor or other sensor detects engine vibration greater than a threshold after changing transmission gears, the transmission may be shifted back to its former gear state. 
     Referring now to  FIG. 19 , a sequence for operating an engine according to the method of  FIG. 18  is shown. The vertical lines at time T 1900 -T 1905  represent times of interest in the sequence.  FIG. 19  shows four plots and the plots are time aligned and occur at the same time. In this example, the vehicle is being maintained at a constant speed and requested wheel torque is varied to maintain the constant vehicle speed. The vehicle has a four cylinder engine. 
     The first plot from the top of  FIG. 19  is a plot of a requested wheel torque versus time. In one example, requested wheel torque is based on accelerator pedal position and vehicle speed. Requested wheel torque increases in the direction of the vertical axis arrow. The horizontal axis represents time and time increases from the left side the figure to the right side of the figure. 
     The second plot from the top of  FIG. 19  is a plot of active transmission gear versus time. The vertical axis represents presently active transmission gear and transmission gears are indicated along the vertical axis. The horizontal axis represents time and time increases from the left side of the figure to the right side of the figure. 
     The third plot from the top of  FIG. 19  is a plot of the actual total number of active engine cylinders versus time. The actual total number of active engine cylinders is listed along the vertical axis. The horizontal axis represents time and time increases from the left side of the figure to the right side of the figure. 
     The fourth plot from the top of  FIG. 19  is a plot of estimated engine fuel consumption versus time. The vertical axis represents estimated engine fuel consumption and estimated engine fuel consumption increases in the direction of the vertical axis arrow. The horizontal axis represents time and time increases from the left side of the figure to the right side of the figure. Trace  1902  represents engine fuel consumption if the engine is operated with the transmission in third gear. Trace  1904  represents engine fuel consumption of the engine is operated with the transmission in second gear. 
     At time T 1900 , the requested wheel torque is a lower middle level and the transmission is in third gear. The actual total number of active engine cylinders is two and the estimated engine fuel consumption is a middle level. 
     Between time T 1900  and time T 1901 , the requested wheel torque gradually increases. The active or present transmission gear is third gear and the actual total number of active engine cylinders is two. The estimated engine fuel consumption for operating the engine in second gear is greater than the estimated engine fuel consumption for operating the engine in third gear. 
     At time T 1901 , the wheel torque has increased to a value where the estimated engine fuel consumption for operating the engine while the transmission is in second gear is less than the estimated fuel consumption for operating the engine while the transmission is in third gear. Therefore, the transmission is downshifted to increase vehicle fuel efficiency. The number of active cylinders remains at a value of two and the estimated fuel consumption increases as the requested wheel torque increases. 
     At T 1902 , the number of active cylinders increases from two to three in response to the increase in requested wheel torque. The requested wheel torque and engine fuel consumption continue to increase. The transmission remains in second gear. 
     At T 1903 , the number of active cylinders increases from three to four in response to the increase in requested wheel torque. The requested wheel torque and engine fuel consumption continue to increase. The transmission remains in second gear as the requested wheel torque increases. 
     At time T 1904 , the requested wheel torque is decreasing and it has decreased to a level where the estimated engine fuel consumption for operating the vehicle in third gear is less than the estimated engine fuel consumption for operating the vehicle in second gear. Therefore, the transmission gear is changed to third gear. The actual total number of active cylinders is also decreased in response to the decreasing requested wheel torque. 
     At  1904 , the requested wheel torque has decreased to a level where the actual total number of active cylinders is reduced from three to two. The transmission remains in third gear and the estimated engine fuel consumption decreases with the decrease in requested engine torque. 
     Referring now to  FIG. 20 , a method for evaluating tow/haul modes for selecting cylinder mode or VDE mode is shown. The method of  FIG. 20  may be included in the system described in  FIGS. 1A-6C . The method of  FIG. 20  may be included as executable instructions stored in non-transitory memory. The method of  FIG. 20  may perform in cooperation with system hardware and other methods described herein to transform an operating state of an engine or its components. 
     It may be more desirable to operate a cylinder with intake and exhaust valves closed and with air or exhaust trapped in the cylinder during an engine cycle because the vehicle may coast for a longer amount of time since the trapped air or exhaust provides a spring like function reducing the cylinder&#39;s braking torque. Further, closing the intake and exhaust valves limits air flow to the catalyst in the exhaust system so that excess fuel may not have to be added to engine exhaust to consume excess oxygen in the catalyst. However, during tow/haul and hill descent modes, it may be desirable to provide higher levels of cylinder braking torque so it may be desirable to open and close intake and exhaust valves. 
     At  2002 , method  2000  judges if the engine is or should be in deceleration fuel cut off mode. In deceleration fuel cut off mode, one or more engine cylinders may be deactivated by stopping fuel flow to the cylinders. Further, gas flow through one or more cylinders may be stopped via deactivating intake valves or intake and exhaust valves of a cylinder being deactivated in closed positions as the engine rotates through an engine cycle. Thus, deactivated cylinders are not combusting air and fuel. In one example, method  2000  judges that the engine should be in a deceleration fuel cut off mode when driver demand decreases from a higher value to a lower value and vehicle speed is greater than a threshold speed. If method  2000  judges that the engine should be in deceleration fuel cut off mode, the answer is yes and method  2000  proceeds to  2004 . Otherwise, the answer is no and method  2000  proceeds to  2020 . 
     At  2020 , method  2000  operates all engine cylinders and all cylinder valves are activated. Further, all engine cylinders combust air and fuel mixtures. Alternatively, less than all engine cylinders may be activated if the driver torque demand is low. Method  2000  proceeds to exit after cylinders are activated. 
     At  2004 , method  2000  judges if the vehicle is in a tow or haul mode. In one example, method  2000  judges that the vehicle is in a tow or haul mode based on an operating state of a pushbutton, switch, or variable in memory. If method  2000  judges that the vehicle is in a tow or haul mode, the answer is yes and method  2000  proceeds to  2006 . Otherwise, the answer is no and method  2000  proceeds to  2030 . 
     A vehicle may have a transmission that shifts according to a first shift schedule (e.g., transmission shifts are based on driver demand torque and vehicle speed) when the vehicle is not in a tow or haul mode. The vehicle&#39;s transmission shifts according to a second shift schedule in a tow or haul mode. The second shift schedule may upshift at higher driver demand torques and higher vehicle speeds than the first shift schedule. The second shift schedule may downshift at higher vehicle speeds to increase driveline braking. 
     At  2006 , method  2000  determines a desired engine brake torque amount for cylinders not combusting air and fuel. In one example, the desired engine brake torque amount may be empirically determined input to a table or function. The table or function may be indexed via driver demand torque, vehicle speed, and transmission gear. The table outputs the desired engine brake torque (e.g., negative torque the engine provides to the driveline to decelerate the vehicle driveline). Method  2000  proceeds to  2008  after determining the desired engine brake torque. 
     At  2008 , method  2000  shifts transmission gears according to a second gear shift schedule. For example, the transmission may upshift from first to second gear at a driver demand torque of greater than 50 N-m and a vehicle speed of 16 KPH. The second transmission gear shift schedule up-shifts transmission gears at higher engine speeds and higher vehicle speeds than the first transmission gear shift schedule. The second transmission gear shift schedule also downshifts transmission gears at higher engine speeds and higher vehicle speeds than the first transmission shift schedule to provide additional engine braking than the first transmission gear shift schedule. The second transmission gear shift schedule up-shifts transmission gears at lower engine speeds and lower vehicle speeds than the third transmission gear shift schedule. The second transmission gear shift schedule downshifts transmission gears at lower engine speeds and lower vehicle speeds than the third transmission shift schedule to provide less engine braking than the third transmission gear shift schedule. Method  2000  proceeds to  2010  after shifting transmission gears according to the second transmission shift schedule. 
     At  2010 , method  2000  determines the cylinder deactivation mode of each deactivated cylinder to achieve the desired engine brake torque provided via deactivated cylinders. Note that the cylinder deactivation mode is different than the cylinder mode. The cylinder deactivation mode defines how valves of a deactivated cylinder are operated whereas the cylinder mode defines the actual total number of active cylinders and the cylinders that are active. In one example, a cylinder with intake and exhaust valves that open and close during an engine cycle without fuel injection (e.g., a first cylinder deactivation mode) and combustion is assigned a first brake torque. A cylinder with intake valves that are held closed over an engine cycle and exhaust valves that open and close over the engine cycle without fuel injection (e.g., a second cylinder deactivation mode) is assigned a second brake torque. A cylinder with intake and exhaust valves that are held closed over an engine cycle without fuel injection (e.g., a third cylinder deactivation mode) is assigned a third brake torque. The first brake torque is greater than the second brake torque, and the second brake torque is greater than the third brake torque. Thus, the engine cylinders may provide three levels of brake torque in three different cylinder deactivation modes, and the desired brake torque may be provided by operating different cylinders at different brake torque producing levels. 
     Further, the assigned brake torque values for each of the three cylinder deactivation modes may be adjusted via adjusting intake valve closing timing. For example, the assigned brake torque values may be increased via retarding intake valve closing timing. Similarly, the assigned brake torque values may be decreased via advancing intake valve closing timing. In one example, a valve timing compensation function indexed via intake valve closing timing outputs a value that is multiplied by the assigned first brake torque, the assigned second brake torque, and the assigned third brake torque to provide valve timing compensated cylinder brake torque values used to determine valve timing compensated brake torque values provided by the cylinders in the different cylinder modes. Additionally, a barometric pressure compensation function indexed by barometric pressure outputs a value that is multiplied by the valve timing compensated brake torque values to provide barometric pressure and valve timing compensated brake torque values provided by the cylinders in the different cylinder deactivation modes Intake and exhaust valve timings for each cylinder deactivation mode may be adjusted to increase or decrease braking torque provided by the three cylinder deactivation modes based on barometric pressure and the desired engine brake torque. For example, if the barometric pressure decreases and desired brake torque increases, intake valve timing in each of the three cylinder deactivation modes may be retarded to compensate for lower barometric pressure and higher desired braking torque. 
     In one example, method  2000  determines valve operation for the engine cylinders according to the desired engine brake torque and the amount of valve timing and barometric pressure compensated brake torque each cylinder provides in the different operating modes. For example, for a four cylinder engine where the desired engine brake torque is 2.5 N-m, the deactivation modes of each cylinder are based on the valve timing and barometric pressure compensated brake torques the cylinders provide in the three different cylinder deactivation modes described above. If a cylinder provides 0.25 N-m of brake torque in the first cylinder deactivation mode, 0.5 N-m in second cylinder deactivation mode, and 1 N-m in the third cylinder deactivation mode, the four cylinder engine is operated with two cylinders in the third cylinder deactivation mode and two cylinders in the first cylinder deactivation mode. 
     The cylinder deactivation mode for each cylinder may be determined by method  2000  evaluating engine brake torque for all engine cylinders operating in the first cylinder deactivation mode. If engine brake torque for operating the engine with all cylinders in the first cylinder deactivation mode is greater than or equal to the desired engine brake torque, all engine cylinders are allowed to operate in the first cylinder deactivation mode where intake valve and exhaust valves are held closed as the engine rotates during an engine cycle. If the engine brake torque for operating the engine with all cylinders in the first cylinder deactivation mode is less than the desired engine brake torque, engine brake torque is determined for operating the engine with one cylinder in the second cylinder deactivation mode and three cylinders in the first cylinder deactivation mode. If engine brake torque for operating the engine with one cylinder in the second cylinder deactivation mode and three cylinders in the first cylinder deactivation mode is greater than or equal to the desired engine brake torque, one cylinder is authorized to operate in the second cylinder deactivation mode and three cylinders are authorized to operate in the first cylinder deactivation mode. Otherwise, engine torque for operating the engine with two cylinders in the second cylinder deactivation mode and two cylinders in the first cylinder deactivation mode is determined. In this way, one after the other, cylinder deactivation modes of each cylinder may be incremented from the first cylinder deactivation mode to the third cylinder deactivation mode until the engine cylinder deactivation modes that provide the desired engine brake torque are determined. 
     If the vehicle is not in tow/haul mode or hill descent mode, it may be determined to be in a fuel economy mode during deceleration conditions. As such, an actual number of engine cylinders with intake and exhaust valves held closed during an engine cycle and not combusting air and fuel may be increased to improve vehicle coasting time and fuel economy. For example, all engine cylinders may be commanded with intake and exhaust valves held closed during an engine cycle. Method  2000  proceeds to  2050 . 
     At  2050 , method  2000  authorizes deactivation of the engine cylinders and their deactivation modes that provide the desired engine brake torque. Valves are authorized activated or deactivated according to the cylinder deactivation modes and fuel is not injected to the cylinders so there is not combustion in the cylinders in the deceleration fuel cut off mode. 
     At  2030 , method  2000  judges if the vehicle is in a hill descent mode. In one example, method  2000  judges that the vehicle is in hill descent mode based on an operating state of a pushbutton, switch, or variable in memory. If method  2000  judges that the vehicle is in a hill descent mode, the answer is yes and method  2000  proceeds to  2032 . Otherwise, the answer is no and method  2000  proceeds to  2040 . 
     In one example, the vehicle is controlled to a requested or desired speed when the accelerator pedal is not applied via controlling negative torque produced via the engine and the vehicle brakes in hill descent mode. The vehicle may enter hill descent mode via releasing the accelerator pedal. Further, engine braking may be controlled in hill descent mode via adjusting engine valve timing. Further still, transmission gears may be shifted to provide a desired braking at the vehicle wheels via the engine. 
     At  2032  method  2000  determines a desired engine brake torque amount for cylinders not combusting air and fuel. In one example, the desired engine brake torque amount may be empirically determined input to a table or function. The table or function may be specific to hill descent mode and different from the table or function for tow/haul mode. The table or function may be indexed via driver demand torque, vehicle speed, and transmission gear. The table outputs the desired engine brake torque (e.g., negative torque the engine provides to the driveline to decelerate the vehicle driveline). Method  2000  proceeds to  2034  after determining the desired engine brake torque. 
     At  2034 , method  2000  shifts transmission gears according to a third gear shift schedule. The third transmission gear shift schedule up-shifts transmission gears at higher engine speeds and higher vehicle speeds than the first and second transmission gear shift schedules. The third transmission gear shift schedule also downshifts transmission gears at higher engine speeds and higher vehicle speeds than the first and second transmission shift schedules to provide additional engine braking than the first and second transmission gear shift schedules. Method  2000  proceeds to  2010  after shifting transmission gears according to the third transmission shift schedule. 
     At  2040  method  2000  determines a desired engine brake torque amount for cylinders not combusting air and fuel. In one example, the desired engine brake torque amount may be empirically determined input to a table or function. The table or function may be specific to fuel cut out mode not part of tow/haul mode or hill descent mode. The table or function may be indexed via driver demand torque, vehicle speed, and transmission gear. The table outputs the desired engine brake torque (e.g., negative torque the engine provides to the driveline to decelerate the vehicle driveline). Method  2000  proceeds to  2042  after determining the desired engine brake torque. 
     At  2042 , method  2000  shifts transmission gears according to a first gear shift schedule. The first transmission gear shift schedule up-shifts transmission gears at lower engine speeds and lower vehicle speeds than the second and third transmission gear shift schedules. The first transmission gear shift schedule also downshifts transmission gears at lower engine speeds and lower vehicle speeds than the second and third transmission shift schedules to provide less engine braking than the second and third transmission gear shift schedules. Method  2000  proceeds to  2010  after shifting transmission gears according to the first transmission shift schedule. 
     In this way, cylinders may be operated in different modes where valves may be activated or deactivated to control engine braking while fuel flow to the engine cylinders is stopped. Different cylinders may be operated in different modes to provide the desired engine brake torque. 
     Referring now to  FIG. 21 , a sequence for operating an engine according to the method of  FIG. 20  is shown. The vertical lines at time T 2100 -T 2108  represent times of interest in the sequence.  FIG. 21  shows six plots and the plots are time aligned and occur at the same time. 
     The first plot from the top of  FIG. 21  is a plot of deceleration fuel cut off state versus time. The vertical axis represents the deceleration fuel cut off state. The engine is in deceleration fuel cut off mode when the trace is at a higher level near the vertical axis arrow. The engine is not in deceleration fuel cut off mode when the trace is at a lower level near the horizontal axis. The horizontal axis represents time and time increases from the left side of the figure to the right side of the figure. 
     The second plot from the top of  FIG. 21  is a plot of hill descent mode state versus time. The vertical axis represents hill descent mode state and the vehicle is in hill descent mode when the trace is at a higher level near the vertical axis arrow. The vehicle is not in hill descent mode when the trace is at a lower level near the horizontal axis. The horizontal axis represents time and time increases from the left side of the figure to the right side of the figure. 
     The third plot from the top of  FIG. 21  is a plot of tow/haul mode state versus time. The vertical axis represents tow/haul mode state and the vehicle is in tow/haul mode when the trace is at a higher level near the vertical axis arrow. The vehicle is not in tow/haul mode when the trace is at a lower level near the horizontal axis. The horizontal axis represents time and time increases from the left side of the figure to the right side of the figure. 
     The fourth plot from the top of  FIG. 21  is a plot of transmission gear versus time. The vertical axis represents transmission gear and transmission gears are indicated along the vertical axis. The horizontal axis represents time and time increases from the left side of the figure to the right side of the figure. 
     The fifth plot from the top of  FIG. 21  is a plot of cylinder poppet valve state versus time. The vertical axis represents cylinder poppet valve state. The poppet valve state may be active (e.g., poppet valves opening and closing during an engine cycle), deactivated (e.g., poppet valves not opening and closing during an engine cycle), partially active (PA) (e.g., intake valves held closed during an engine cycle and exhaust valves opening and closing over the engine cycle). The horizontal axis represents time and time increases from the left side of the figure to the right side of the figure. 
     The sixth plot from the top of  FIG. 21  is a plot of fuel injection state versus time. The vertical axis represents fuel injection state and fuel injection is activated when the trace is near the vertical axis arrow. Fuel injection is deactivated when the trace is near the horizontal axis. The horizontal axis represents time and time increases from the left side of the figure to the right side of the figure. 
     At time  2100 , engine cylinders are active and cylinder valves are opening and closing over the engine cycle as the engine rotates and combusts air and fuel since the poppet valves are active and deceleration fuel cut out is not indicated. The vehicle is not in hill descent mode nor is it in tow/haul mode. The vehicle&#39;s transmission is in third gear and all cylinder poppet valves are active (e.g., opening and closing over the engine cycle). Fuel injection is active and fuel is being supplied to the engine cylinders. 
     At  2101 , the engine enters deceleration fuel cut off mode. The engine may enter deceleration fuel cut off mode in response to a low driver demand torque and vehicle speed greater than a threshold. The vehicle is not in hill descent mode nor is it in tow/haul mode. The vehicle&#39;s transmission is in third gear and all cylinder poppet valves are deactivated (e.g., not opening and closing over the engine cycle). The cylinder poppet valves are deactivated so that the engine cylinders are in a third cylinder deactivation mode in response to a low requested engine brake torque (not shown). Further, exhaust gas or fresh air is trapped in the cylinder so that there is a spring effect on the piston. The closed intake and exhaust valves reduce engine pumping losses and may extend the distance that the vehicle coasts. Closing the engine&#39;s intake and exhaust valves also stops the engine from pumping fresh air to the catalyst in the engine&#39;s exhaust system so that the catalyst is not cooled as much as if fresh air flowed to the catalyst. Further, the amount of oxygen stored in the catalyst is not increased so that catalyst efficiency may be high if the engine cylinders resume combustion. Fuel injection is also ceased to the engine&#39;s cylinders so that there is no combustion in the engine cylinders. 
     At time  2102 , then engine exits deceleration fuel cut off mode and the cylinder&#39;s poppet valves are reactivated as indicated by the poppet valve state trace. Fuel injection is also reactivated and combustion begins in the engine cylinders. The engine may exit deceleration fuel cut off in response to an increase in driver demand torque or vehicle speed being less than a threshold. The vehicle is not in hill descent mode nor is it in tow/haul mode. The vehicle&#39;s transmission is in third gear. 
     At time  2103 , the vehicle enters hill descent mode. The vehicle may enter hill descent mode via a driver applying a pushbutton or other input device. The vehicle is not in deceleration fuel cut off mode and it is not in tow/haul mode. The vehicle&#39;s transmission is in third gear and the cylinder&#39;s poppet valves are active. Fuel is also injected to engine cylinders and the engine combusts air and fuel. 
     At time  2104 , the engine enters deceleration fuel cut off mode while in hill descent mode. The vehicle is not in tow/haul mode and the transmission is in third gear. The cylinder&#39;s poppet valves are partially deactivated (e.g., intake valves are held closed during an engine cycle and exhaust valves open and close during the engine cycle) in response to a middle level engine brake torque request while the engine rotates. Engine cylinders are in a second cylinder deactivation mode when the engine brake torque is at the middle level. However, engine cylinders may enter the first mode if the vehicle is accelerating at a higher rate than is desired. Likewise, the engine cylinders may enter the third cylinder deactivation mode if the vehicle is decelerating faster than is desired. Fuel injection is deactivated so that there is no combustion in engine cylinders. 
     At time  2105 , the vehicle exits deceleration fuel cut off mode in response to increasing driver demand torque or vehicle speed being less than a threshold speed (not shown). The vehicle remains in hill descent mode and the transmission is in third gear. The vehicle is not in tow/haul mode and the cylinder poppet valves are reactivated. Fuel injection to engine cylinders is also reactivated so that the engine cylinders resume combusting air and fuel. 
     Between time  2105  and time  2106 , the vehicle exits hill descent mode. The driver may request exiting hill descent mode via applying an input to the vehicle or engine controller. The other engine/vehicle states remain at their previous levels. 
     At time  2106 , the vehicle enters tow/haul mode. The vehicle may enter tow/haul mode via a driver applying a pushbutton or switch that provides input to the vehicle or engine controller. The other engine/vehicle states remain at their previous levels. 
     At time  2107 , the engine enters deceleration fuel cut off mode in response to low driver demand torque and vehicle speed exceeding a threshold speed. The vehicle is also in tow/haul mode. The vehicle&#39;s transmission is downshifted into second gear shortly after entering deceleration fuel cut off mode to increase engine braking via increasing engine speed (not shown). All engine cylinder poppet valves remain active in response to a higher level engine brake torque request (not shown). Fuel injection is ceased to engine cylinders and the engine is not combusting air and fuel as the engine rotates. Operating all cylinder valves while the engine throttle is closed (not shown) increases engine pumping losses and engine braking torque. 
     At  2108 , the vehicle exits deceleration fuel cut off mode in response to an increase in driver demand torque or engine speed being reduced to less than a threshold. The vehicle remains in tow/haul mode and the cylinder poppet valves continue to be activated. 
     In this way, cylinder modes in which cylinder poppet valves are operated in different ways may be used to vary engine braking torque so that a desired engine braking torque may be provided by the vehicle&#39;s engine. Further, some engine cylinders may be in a first operating mode while other engine cylinders are in a second or third operating mode so that the desired engine braking torque may be provided. 
     Referring now to  FIG. 22 , a method for selecting a cylinder mode from available cylinder modes is shown. The method of  FIG. 22  may be included in the system described in  FIGS. 1A-6C . The method of  FIG. 22  may be included as executable instructions stored in non-transitory memory. The method of  FIG. 22  may perform in cooperation with system hardware and other methods described herein to transform an operating state of an engine or its components. 
     At  2202 , method  2200  judges if basic conditions are present to enable cylinder modes where cylinders may be deactivated. Basic conditions may include but are not limited to engine temperature being greater than a threshold, exhaust after treatment temperature greater than a threshold, battery start of charge greater than a threshold, and engine speed greater than a threshold. Method  2200  verifies whether or not the conditions are present via monitoring various system sensors. If method  2200  judges that basis conditions for cylinder deactivation or variable displacement engine operation are present, the answer is yes and method  2200  proceeds to  2204 . Otherwise, the answer is no and method  2200  proceeds to  2220 . 
     At  2220 , method  2200  requests all engine cylinders are active and combusting air and fuel Intake and exhaust valves of activated cylinders open and close during an engine cycle so that air and combustion products flow through activated cylinders. Spark and fuel are also activated so that fuel-air mixtures are combusted in activated cylinders. Method  2200  proceeds to exit. 
     At  2204 , method  2200  estimates noise, vibration, and harshness (NVH) in available cylinder modes. In one example, a noise table outputs empirically determined expected audible noise levels for the engine/vehicle. The noise table is indexed via the actual total number of active engine cylinders, engine speed, and engine torque. A vibration table outputs empirically determined expected audible noise levels for the engine/vehicle. The vibration table is indexed via the cylinder mode, engine speed, and engine torque. Noise and vibration values are output for present engine speed, engine speed after a transmission gear shift, present driver demand torque, and driver demand torque after a transmission shift. Additionally, method  2200  may compare outputs of vibration sensors (e.g., an engine knock sensor) and audible sensors to threshold levels for the purpose of eliminating presently active cylinder deactivation modes that may not provide desired levels of noise and vibration. Method  2200  proceeds to  2206 . 
     At  2206 , method  2200  evaluates noise and vibration outputs from the noise and vibration tables, if the expected noise level of a table output exceeds a threshold or if the expected vibration level of a table output exceeds a threshold, the cylinder mode that provided the expected noise and vibration is eliminated from presently available cylinder modes. For example, if expected engine noise for operating a four cylinder engine in a second cylinder mode with two cylinder active cylinders at 2000 RPM exceeds a threshold at the present driver demand torque or driver demand torque after a transmission shift, the second cylinder mode at 2000 RPM is eliminated from a list of available cylinder modes. 
     Alternatively, or additionally, method  2200  may compare noise and vibration sensor outputs to threshold levels. If engine noise exceeds a threshold in a presently activated cylinder mode, the presently activated cylinder mode is eliminated from available cylinder modes so that a cylinder mode that provides less engine noise may be selected. Likewise, if engine vibration exceeds a threshold in a presently activated cylinder mode, the presently activated cylinder mode is eliminated from available cylinder modes so that a cylinder mode that provides less engine vibration may be selected. 
     Additionally, method  2200  may allow cylinder modes where expected cylinder blow through (e.g., air flow from the engine&#39;s intake manifold to the engine&#39;s exhaust manifold that does not participate in combustion) immediately following a cylinder mode change is expected to be less than a threshold value. It may be desirable to avoid cylinder mode changes where cylinder blow through is higher than the threshold to avoid disturbing oxygen in a catalyst downstream of the engine. Engine cylinder blow through amount may be determined according to U.S. patent application Ser. No. 13/293,015 filed Nov. 9, 2011, which is hereby fully incorporated by reference for all purposes. In one example, a table or function outputs an engine or cylinder blow through amount based on cylinder mode, engine speed, and cylinder valve timing. If output from the table is less than the threshold amount, the cylinder mode may be allowed. Method  2200  proceeds to  2208 . 
     At  2208 , method  2200  allows cylinder modes that are available and that have not been eliminated from the available cylinder modes. Further, transmission gears that are available and that have not been eliminated are allowed. Cylinder modes may be allowed so that they may eventually be selected for operating the engine at  716  of  FIG. 7 . A cylinder mode where all engine cylinders are activated is always an allowed cylinder mode unless engine or valve degradation is present. In one example, a matrix that includes cells representing cylinder modes is used to keep track of allowed and eliminated cylinder modes. Cylinder modes may be allowed by installing a value of one in cells that correspond to available cylinder modes. Cylinder modes may be eliminated by installing a value of zero in cells that correspond to cylinder modes that are not available or that are eliminated from engine operation. As previously noted, different cylinder modes may have a same number of actual total active cylinders while having different active cylinders. For example, if it is determined to be desirable to operate three cylinders of a four cylinder engine to meet driver demand torque, cylinder mode numbers three and four may be allowed where cylinder mode three has a firing order of 1-3-2 and cylinder mode four has a firing order of 3-4-2. In one engine cycle, cylinder mode three may be active. During a subsequent engine cycle, cylinder mode four may be active. In this way, the engine firing order may be varied while maintaining an actual total number of active cylinders. Method  2200  proceeds to exit. 
     In this way, cylinder deactivation modes may be made available or eliminated may be identified. Further, basic conditions may have to be met before available cylinder modes may be made allowable cylinder modes for engine operation. 
     Referring now to  FIG. 23 , a method for controlling engine intake manifold absolute pressure (MAP) during a deceleration fuel cut off mode is shown. The method of  FIG. 23  may be included in the system described in  FIGS. 1A-6C . The method of  FIG. 23  may be included as executable instructions stored in non-transitory memory. The method of  FIG. 23  may perform in cooperation with system hardware and other methods described herein to transform an operating state of an engine or its components. 
     At  2302 , method  2300  judges if the engine is or should be in deceleration fuel cut off mode. In deceleration fuel cut off mode, one or more engine cylinders, which may include all engine cylinders, may be deactivated by stopping fuel flow to the cylinders. Further, gas flow through one or more cylinders may be stopped via deactivating intake valves or intake and exhaust valves of a cylinder being deactivated in closed positions as the engine rotates through an engine cycle. In one example, method  2300  judges that the engine should be in a deceleration fuel cut off mode when driver demand decreases from a higher value to a lower value and vehicle speed is greater than a threshold speed. If method  2300  judges that the engine should be in deceleration fuel cut off mode, the answer is yes and method  2300  proceeds to  2304 . Otherwise, the answer is no and method  2000  proceeds to  2320 . 
     At  2320 , method  2300  operates the engine to provide a desired amount of torque. The desired amount of torque may be a driver demand torque or based on the driver demand torque. Valves of the engine are activated as requested to provide the desired torque and the engine combusts air and fuel to provide the desired torque. Method  2300  proceeds to exit after providing the desired amount of torque. 
     At  2304 , method  2300  determines a desired intake manifold pressure and an actual total number of cylinder intake valve opening events (e.g., intake valves of each cylinder open once during an intake stroke of the cylinder with opening intake valves) or intake strokes of cylinders inducting air to reduce intake manifold pressure to a desired intake manifold pressure. The actual total number of cylinder intake valve opening events may provide a better inference of intake manifold pressure than time to pump the intake manifold pressure down. In one example, the methods described in U.S. Pat. No. 6,708,102 or 6,170,475, which are hereby fully incorporated for all purposes, may be used to estimate intake manifold pressure for a desired number of intake valve opening events or intake strokes into the future. For example, the throttle may follow a predetermined trajectory from its current position to a fully closed position in response to entering deceleration fuel cut off mode. The predicted throttle position may be estimated from the predetermined trajectory via the following equation:
 
θ( k+ 1)=θ( k )+[θ( k )−θ( k− 1)]
 
where θ(k+1) is the estimate of throttle position at the next engine intake event; θ(k) is the measured throttle position at the present engine intake event; and θ(k−1) is the measured throttle position at the previous engine intake event.
 
     The gas in the engine intake manifold is fresh air and the pressure in the engine intake manifold is directly related to the cylinder air charge. The throttle position, intake manifold pressure, intake manifold temperature, and engine speed are determined from the various engine sensors. To determine intake manifold pressure evolution, the starting point is a standard dynamic model governing the change of pressure in the intake manifold as follows: 
               P   m     =       RT   V     ⁢     (     MAF   -     M   cyl       )             
where, T is the temperature in the intake manifold as sensed by intake manifold temperature sensor, V is the volume of the intake manifold, R is the specific gas constant, MAF is the mass flow rate into the intake manifold and M cyl  is the flow rate into the cylinder. The mass flow into the cylinders (M cyl ) is represented as a near function of intake manifold pressure with the slope and offset being dependent on engine speed and ambient conditions as follows:
 
               M   cyl     =           α   1     ⁡     (   N   )       ⁢     P   m       -         α   2     ⁡     (   N   )       ⁢       P   amb       P   amb_nom                 
where P amb  and P amb   _   nom  are the current ambient pressure and the nominal value of the ambient pressure (e.g. 101 kPa) The engine pumping parameters α 1 (N) and α 2 (N) are regressed from the static engine mapping data obtained at nominal ambient conditions. After substituting this expression into the dynamic equation, for intake manifold pressure and differentiating both sides to obtain the rate of change of the pressure in the intake manifold, we obtain:
 
                 P   ¨     m     =       RT   V     [         d   dt     ⁢   MAF     -       α   1     ⁢       P   .     m       -         α   .     1     ⁢     P   m       -         α   .     2     ⁢       P   amb       P   amb_nom           ]           
The dynamics governing change of engine speed are slower than the intake manifold dynamics. A good tradeoff between performance and simplicity is to retain α 1 (slope) and neglect α 2 (offset). With this simplification, the second derivative of P m  is given by:
 
                 P   ¨     m     =       RV   V     [         d   dt     ⁢   MAF     -       α   1     ⁢       P   .     m       -         α   .     1     ⁢     P   m         ]           
To discretize the above equation, dP m (k) is defined as a discrete version of the time derivative of P m , that is dP m  (k)=(P m (k+1)−P m (k))/Δt, to obtain:
 
                 dP   m     ⁡     (     k   +   1     )       =     (     1   -     Δ   ⁢           ⁢   t   ⁢           ⁢       α   1     ⁡     (     N   ⁢           ⁢     (   k   )     ⁢     RT   V       )       ⁢           ⁢     dP   m       +                         ⁢               RT   V     [           ⁢                   ⁢     MAF   ⁡     (     k   +   1     )         -     MAF   ⁡     (     k   -   1     )         ]     -         RT   V     ⁡     [         α   1     ⁡     (     N   ⁡     (     k   +   1     )       )       -       α   1     ⁡     (     N   ⁡     (   k   )       )         ]       ⁢       P   m     ⁡     (   k   )                         
Thus, this equation defines the predicted rate of change of the intake manifold pressure one engine event into the future, which is used to determine the future values of intake manifold pressure. However, at time instant k, the signals from the next (k+1) instant are not available. To implement the right hand side, instead of its value at, time k+1, we use the one event ahead predicted value of the MAF signal at time k obtained by using, the one event ahead prediction of the throttle position as follows:
 
                 MAF     +   1       ⁡     (   k   )       =         P   amb       P   amb_nom       ⁢         T   amb_nom       T   amb         ⁢   C   ⁢           ⁢     (       θ     +   1       ⁡     (   k   )       )     ⁢   Fn_subsonic   ⁢           ⁢     (           P   m     ⁡     (   k   )       +     Δ   ⁢           ⁢       tdP   m     +   1       ⁡     (     k   -   1     )             P   amb       )             
where P amb  and P amb   _   nom  are current and nominal (i.e., 101 kPa) absolute ambient pressures, T amb  and T amb   _   nom  are current and nominal (i.e., 300 K) absolute ambient temperatures, and C(θ) is the throttle sonic flow characteristic obtained from static engine data. Fn_subsonic is the standard subsonic flow correction:
 
               Fn   subsonic     =     {             14.96501   ⁢           [         (       P   m       P   amb       )     1.42959     -       (       P   m       P   amb       )     1.7148       ]               if   ⁢             ⁢             ⁢       P   m       P   amb         ≥   0.52845             1.0           if   ⁢           ⁢       P   m       P   amb         &lt;   0.52845           }           
where P m  (k) is the current measurement of intake manifold pressure. For in-vehicle implementation, the Fn_subsonic function can be implemented as a tabulated lookup function of the pressure ratio. In this case, the magnitude of the slope should be invited to prevent oscillatory behavior under wide open throttle conditions, possibly by extending the zero crossing of the function to a value of the pressure ratio slightly over 1.
 
     Several different choices are available to obtain the quantity MAF(k) to be used in determining the future rate of change in the intake manifold pressure. The following formula, which uses the previous value of predicted throttle position and current value of the manifold pressure, provides the best performance in terms of overshoot and stability at wide open throttle: 
     
       
         
           
             
               MAF 
               ⁢ 
               
                   
               
               ⁢ 
               
                 ( 
                 k 
                 ) 
               
             
             = 
             
               
                 
                   P 
                   amb 
                 
                 
                   P 
                   amb_nom 
                 
               
               ⁢ 
               
                 
                   
                     T 
                     amb_nom 
                   
                   
                     T 
                     amb 
                   
                 
               
               ⁢ 
               C 
               ⁢ 
               
                   
               
               ⁢ 
               
                 ( 
                 
                   
                     θ 
                     
                       + 
                       1 
                     
                   
                   ⁡ 
                   
                     ( 
                     
                       k 
                       - 
                       1 
                     
                     ) 
                   
                 
                 ) 
               
               ⁢ 
               
                   
               
               ⁢ 
               Fn_subsonic 
               ⁢ 
               
                   
               
               ⁢ 
               
                 ( 
                 
                   
                     
                       P 
                       m 
                     
                     ⁡ 
                     
                       ( 
                       k 
                       ) 
                     
                   
                   
                     P 
                     amb 
                   
                 
                 ) 
               
             
           
         
       
     
     To avoid predicting the engine speed, instead of subtracting the present value of α 1  from its one, step ahead prediction, we approximate α 1  by subtracting the one event old value from the present. The above changes result in the dP m  signal corresponding to the one event ahead predicted value of the time derivative of P m , i.e., the rate of change of the future intake manifold pressure: 
     
       
         
           
             
               
                 dP 
                 n 
                 
                   + 
                   1 
                 
               
               ⁡ 
               
                 ( 
                 k 
                 ) 
               
             
             = 
             
               
                 
                   ( 
                   
                     1 
                     - 
                     
                       Δ 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       t 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       
                         
                           α 
                           1 
                         
                         ⁡ 
                         
                           ( 
                           
                             N 
                             ⁡ 
                             
                               ( 
                               k 
                               ) 
                             
                           
                           ) 
                         
                       
                       ⁢ 
                       
                         RT 
                         V 
                       
                     
                   
                   ) 
                 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 
                   
                     dP 
                     m 
                     
                       + 
                       1 
                     
                   
                   ⁡ 
                   
                     ( 
                     
                       k 
                       - 
                       1 
                     
                     ) 
                   
                 
               
               + 
               
                 
                     
                   
                       
                   
                     
                 
                 ⁢ 
                 
                     
                   
                     
                       
                         RT 
                         V 
                       
                       [ 
                       
                           
                       
                       ⁢ 
                       
                         
                           
                               
                               
                           
                           ⁢ 
                           
                             
                               MAF 
                               
                                 + 
                                 1 
                               
                             
                             ⁡ 
                             
                               ( 
                               k 
                               ) 
                             
                           
                         
                         - 
                         
                           MAF 
                           ⁡ 
                           
                             ( 
                             k 
                             ) 
                           
                         
                       
                       ] 
                     
                     - 
                     
                       
                         
                           RT 
                           V 
                         
                         ⁡ 
                         
                           [ 
                           
                             
                               
                                 α 
                                 1 
                               
                               ⁡ 
                               
                                 ( 
                                 
                                   N 
                                   ⁢ 
                                   
                                       
                                   
                                   ⁢ 
                                   
                                     ( 
                                     k 
                                     ) 
                                   
                                 
                                 ) 
                               
                             
                             - 
                             
                               
                                 α 
                                 1 
                               
                               ⁡ 
                               
                                 ( 
                                 
                                   N 
                                   ⁢ 
                                   
                                       
                                   
                                   ⁢ 
                                   
                                     ( 
                                     
                                       k 
                                       - 
                                       1 
                                     
                                     ) 
                                   
                                 
                                 ) 
                               
                             
                           
                           ] 
                         
                       
                       ⁢ 
                       
                         
                           P 
                           m 
                         
                         ⁡ 
                         
                           ( 
                           k 
                           ) 
                         
                       
                     
                   
                 
               
             
           
         
       
     
     Note that the value of dP m   +1  (k) depends only on the signals available at intake event k. Hence, it can be used in the prediction of intake manifold pressure as follows:
 
 P   m   +1 ( k )= P   m ( k )+Δ tdP   m   +1 ( k− 1)
 
 P   m   +2 ( k )= P   m ( k )+Δ tdP   m   +1 ( k− 1)+Δ tdP   m   +1 ( k )
 
where P m   +1  (k) and P m   +2  (k) are one and two steps ahead predictions of the intake manifold pressure. The manifold pressure evolution equations may be extended beyond two intake events into the future to a number of intake events that provides the desired intake manifold pressure. In one example, the desired intake manifold pressure during deceleration mode may be empirically determined and stored in memory. For example, the desired intake manifold pressure may be empirically determined and indexed in memory based on atmospheric pressure and vehicle speed. In one example, the desired engine intake manifold pressure is a pressure in the intake manifold when the engine is operating at idle speed when driver demand torque is zero or substantially zero (e.g., less than 10 N-m. Further, the desired intake manifold pressure may be adjusted responsive to ambient pressure. For example, if ambient pressure increases, desired intake manifold pressure may be decreased. Method  2300  proceeds to  2306  after determining the desired engine intake manifold pressure and the number of cylinder intake even s to achieve the desired intake manifold pressure.
 
     At  2306 , method  2300  fully closes the engine throttle and closes all engine intake events after the number of intake events determined a  2304  to provide the desired intake manifold pressure has been performed. For example, if it is determined at  2304  that the desired intake manifold pressure is 75 kPa and that the desired intake manifold pressure may be reached as the throttle closes in four cylinder intake valve opening events, intake valves of cylinders, and in some cases exhaust valves, are closed such that a total actual number of cylinder intake events after entering deceleration fuel cut off is four. In this way, the cylinder valves are closed based on an actual total number of intake valve opening events since a deceleration fuel cut off mode request to provide a desired intake manifold pressure. Since the cylinder valves are closed, the engine may be started subsequently without having to evacuate air from the intake manifold Consequently, less fuel may be used to richen engine exhaust to improve catalyst efficiency. Further the engine may be operated with less spark retard when reactivating cylinders since cylinder charge is less than al full charge. Method  2300  proceeds to  2308 . 
     At  2308 , method  2300  closes off the engine intake manifold to all vacuum consumers. Vacuum consumers may include but are not limited to vacuum reservoirs; vehicle brakes; heating, ventilation, and cooling systems; and vacuum actuators such as turbocharger waste gates. However, if vacuum in some systems (e.g., brakes) is reduced to less than a threshold, systems may again have access to the engine intake manifold for vacuum via opening a valve  176  as shown in  FIG. 1B . Further, the valves may be reactivated during such conditions so that the engine may provide additional vacuum to vacuum consumers. In one example, vacuum consumers are provided selective access to engine intake manifold pressure via one or more solenoid valves. Method  2300  proceeds to  2310 . 
     At  2310 , method  2300  operates a vacuum source, to maintain engine intake manifold pressure at the desired level. If air leaks by the throttle, intake manifold pressure may increase so that if the engine is restarted with intake manifold pressure at atmospheric pressure, more fuel may be used to start the engine than is desired. Consequently, engine fuel consumption may increase more than is desired if the engine is restarted with a higher intake manifold pressure than is desired. Therefore, the vacuum source may be activated in response to intake manifold pressure greater than the desired intake manifold pressure so that the intake manifold pressure is less than atmospheric pressure (e.g., a vacuum is in the intake manifold). The vacuum source may be supplied electrical power generated via the vehicle&#39;s kinetic energy or a battery. Additionally, the vacuum source may be activated to evacuate air from a vacuum reservoir in response to low vacuum in the vacuum reservoir. Method  2300  proceeds to  2312 . 
     At  2312 , method  2300  ceases fuel flow and spark to engine cylinders. Air inducted during the intake events after the throttle begins to close, the intake events corresponding to the actual number of intake valve opening events determined at  2304 , is combined with fuel and combusted before fuel and spark delivery to engine cylinders is ceased. Method  2300  proceeds to  2314 . 
     At  2314 , method  2300  judges if conditions are present to exit deceleration fuel cut off. In one example, deceleration fuel cut off may be exited in response to a driver demand torque greater than a threshold or vehicle speed less than a threshold. If method  2300  judges that conditions are present to exit decoration fuel cut off mode, the answer is yes and method  2300  proceeds to  2316 . The engine continues to rotate during decoration fuel cut off since a portion of the vehicle&#39;s kinetic energy may be transferred to the engine. Otherwise, method  2300  returns to  2310 . 
     At  2316 , method  2300  reactivates cylinder valves so that the valves open and close during an engine cycle. Further, fuel flow and spark delivery are also provided to the cylinders. Combustion is resumed in the cylinders and the engine throttle position is adjusted to provide the desired engine air flow and engine torque. The cylinder valve timing and throttle positions may be empirically determined values stored in memory indexed by engine speed and engine demand torque (e.g., driver demand torque). Method  2300  proceeds to exit. 
     In this way, engine intake manifold pressure may be controlled to improve cylinder reactivation and combustion in engine cylinders so that fuel consumption may be reduced and catalyst balance (e.g., balance between hydrocarbons and oxygen in the catalyst) may be restored with less fuel being provided to the engine and/or catalyst. 
     Referring now to  FIG. 24 , a sequence for operating an engine according to the method of  FIG. 23  is shown. The vertical lines at time T 2400 -T 2408  represent times of interest in the sequence.  FIG. 24  shows six plots and the plots are time aligned and occur at the same time. 
     The first plot from the top of  FIG. 24  is a plot of deceleration fuel cut off state versus time. The vertical axis represents the deceleration fuel cut off state. The engine is in deceleration fuel cut off mode when the trace is at a higher level near the vertical axis arrow. The engine is not in deceleration fuel cut off mode when the trace is at a lower level near the horizontal axis. The horizontal axis represents time and time increases from the left side of the figure to the right side of the figure. 
     The second plot from the top of  FIG. 24  is a plot of engine manifold absolute pressure (MAP) versus time. The vertical axis represents MAP and MAP increases in the direction of the vertical axis arrow. The horizontal axis represents time and time increases from the left side of the figure to the right side of the figure. Horizontal line  2402  represents a desired MAP during deceleration fuel cut off mode. 
     The third plot from the top of  FIG. 24  is a plot of engine throttle position versus time. The vertical axis represents throttle position and throttle position increases in the direction of the vertical axis arrow. The horizontal axis represents time and time increases from the left side of the figure to the right side of the figure. 
     The fourth plot from the top of  FIG. 24  is a plot of vacuum source state versus time. The vertical axis represents vacuum source operating state (e.g., vacuum pump operating state) and the vacuum source is active when the trace is near the vertical axis arrow. The vacuum source is not active when the trace is near the horizontal axis. The horizontal axis represents time and time increases from the left side of the figure to the right side of the figure. 
     The fifth plot from the top of  FIG. 24  is a plot of fuel delivery state versus time. The vertical axis represents fuel delivery state and fuel is delivered to engine cylinders when the trace is near the vertical axis arrow. Fuel is not delivered to engine cylinders when the trace is near the horizontal axis. The horizontal axis represents time and time increases from the left side of the figure to the right side of the figure. 
     The sixth plot from the top of  FIG. 24  is a plot of vacuum consumer state versus time. The vertical axis represents vacuum consumer state and the vacuum consumer state is active when the trace is near the vertical axis arrow. The vacuum consumers are not active when the trace is near the horizontal axis. Vacuum consumers are not in pneumatic communication with the engine intake manifold when the vacuum consumer trace is at a lower level. Vacuum consumers are in pneumatic communication with the engine intake manifold when the vacuum consumer trace is at a higher level. The horizontal axis represents time and time increases from the left side of the figure to the right side of the figure. 
     At time T 2400 , the engine is not in deceleration fuel cut off mode as indicated by the deceleration fuel cut off state being at a lower level. The engine MAP is relatively high indicating a higher engine load. The throttle position is open a large amount and the vacuum device state is off to indicate that the vacuum source is not activated. Fuel is being supplied to engine cylinders as indicated by the fuel state being at a high level. The vacuum consumers are operating and able to consume vacuum based on the vacuum consumer state. 
     At time  2402 , the engine transitions into deceleration fuel cut off mode as indicated by the desired fuel cut off state trace moving from a lower level to a higher level. The engine may enter deceleration fuel cut off mode in response to a reduction in driver demand torque and vehicle speed being greater than a threshold. The throttle is closed in response to entering deceleration fuel cut off mode. Likewise, fuel flow is cut off to engine cylinders as indicated by the fuel state trace being at a lower level. The vacuum consumer state moves to a lower level to indicate that vacuum consumers are blocked from receiving vacuum from the engine intake manifold. By blocking air flow into the engine intake manifold from vacuum consumers, intake manifold pressure may be reduced so that a large amount of fuel is not necessary to restart the engine with stoichiometric air-fuel ratios in engine cylinders. Cylinder valves are also closed in response to entering deceleration fuel cut off mode. A total actual number of intake valve opening events may be performed in response to entering deceleration fuel cut off mode before air flow through engine cylinders is ceased by closing cylinder intake valves over one or more engine cycles while the engine continues to rotate. The total actual number of intake valve opening events may be a number that provides a desired engine intake manifold pressure. In some examples, engine intake valves and exhaust valves may be closed over an engine cycle in response to entering deceleration fuel cut off mode. 
     Between  2402  and  2404 , MAP is reduced and the engine remains in deceleration fuel cut off mode. MAP is reduced to a level of desired MAP  2402 . In one example, MAP is reduced to desired MAP  2402  by opening cylinder intake valves an actual total number of times based on an estimate of intake manifold pressure reaching  2402 . 
     At  2404 , MAP increases to a level above  2402  due to air leakage past the engine throttle or other air flow into the engine intake manifold. The vacuum source is activated in response to the increased MAP so that MAP is lowered to  2402 . The engine remains in deceleration fuel cut off mode and the throttle remains closed. The engine continues to rotate (not shown) and fuel flow to engine cylinders is stopped. Cylinder intake valves remain deactivated and closed over each engine cycle (not shown). The vacuum source is deactivated shortly after being activated in response to MAP being less than  2402 . The vacuum source state indicates vacuum source activation (ON) and deactivation (OFF). 
     At  2406 , MAP increases to a level above  2402  for a second time due to air leakage past the engine throttle or other air flow into the engine intake manifold. The vacuum source is activated in response to the increased MAP so that MAP is lowered to  2402 . The engine remains in deceleration fuel cut off mode and the throttle remains closed. The engine continues to rotate (not shown) and fuel flow to engine cylinders is stopped. Cylinder intake valves remain deactivated and closed over each engine cycle (not shown). The vacuum source is deactivated shortly after being activated in response to MAP being less than  2402 . The vacuum source state indicates vacuum source activation (ON) and deactivation (OFF). 
     At time T 2408 , the engine exits deceleration fuel cut off mode while intake manifold pressure is low. The engine may exit deceleration fuel cut off mode in response to an increase in driver demand torque. The lower intake manifold pressure may reduce the use of spark retard and conserve fuel to reactivate engine cylinders and the catalyst in the engine exhaust system. The engine cylinders are reactivated by supplying fuel to the cylinders and reactivating cylinder valves (not shown). The vacuum consumers are also reactivated by allowing communication between the vacuum consumers and the engine intake manifold. MAP increases as the throttle is opened. 
     In this way, MAP may be controlled during deceleration fuel cut off mode to reduce fuel consumption. Further, driveline torque disturbances may be reduced since the engine is started with a smaller air charge as compared to if the engine is started with atmospheric pressure in the engine intake manifold. 
     Referring now to  FIG. 25 , a method for controlling engine intake manifold absolute pressure (MAP) during cylinder reactivation after entering a deceleration fuel cut off mode is shown. The method of  FIG. 25  may be included in the system described in  FIGS. 1A-6C . The method of  FIG. 25  may be included as executable instructions stored in non-transitory memory. The method of  FIG. 25  may perform in cooperation with system hardware and other methods described herein to transform an operating state of an engine or its components. 
     At  2502 , method  2500  judge if cylinders and valves are deactivated during a deceleration fuel cut off mode. In one example, method  2500  may judge that engine cylinders are deactivated (e.g., not combusting air and fuel mixtures while the engine rotates) and valves are deactivated (e.g., held closed, not opening and closing as the engine rotates over an engine cycle) when a bit in memory is a predetermined value. Note that all or only a fraction of engine cylinders may be deactivated. If method  2500  judges that engine cylinders and valves are deactivated during deceleration fuel cut off mode, the answer is yes and method  2500  proceeds to  2504 . Otherwise, the answer is no and method  2500  proceeds to  2540 . 
     At  2540 , method  2500  operates engine cylinders and valves to provide a desire torque. The desired torque may be based on accelerator pedal position or a controller determined torque. The engine cylinders are activated by supplying fuel to the cylinders. The valves are activated by enabling valve operators. Further, volumetric efficiency actuators are adjusted to different positions than at  2508  for a same engine speed and torque demand to improve vehicle emissions and fuel economy. Method  2500  proceeds to exit. 
     At  2504 , method  2500  judges if cylinder reactivation is requested. Cylinder reactivation may be requested in response to an increase in driver demand torque or vehicle speed being less than a threshold speed. If method  2500  judges that cylinder reactivation is requested, the answer is yes and method  2500  proceeds to  2506 . Otherwise, method  2500  proceeds to  2550 . 
     At  2550 , method  2500  maintains the cylinders in a deactivated state. Fuel is not supplied to the cylinders and the cylinder valves remain deactivated. Method  2500  proceeds to exit. 
     At  2506 , method  2500  judges if engine intake manifold pressure is greater than a threshold pressure. If engine intake manifold pressure is greater than a threshold pressure, the engine cylinders may produce more torque than is desired or spark timing may be retarded to reduce engine torque. If engine intake manifold pressure is greater than desired, cylinders may combust more fuel than is desired to provide stoichiometric exhaust gases. Therefore, it may be desirable to reduce engine intake manifold pressure as soon as possible when reactivating engine cylinders so that fuel may be conserved. If method  2500  judges that intake manifold pressure is greater than the threshold pressure, the answer is yes and method  2500  proceeds to  2508 . Otherwise, the answer is no and method  2500  proceeds to  2520 . The threshold pressure may vary with engine speed, vehicle speed, and ambient pressure. 
     At  2520 , method  2500  adjusts engine volumetric efficiency actuators and the engine throttle based on engine speed and driver demand torque. In one example, driver demand torque is based on accelerator pedal position and vehicle speed. The engine volumetric efficiency actuators may include but are not limited to engine camshafts, charge motion control valves, and variable plenum volume valves. The positions of the volumetric efficiency actuators may be empirically determined and stored to a table in memory that is indexed via driver demand torque and engine speed. Different tables output different positions for the camshafts, charge motion control valves, and the variable plenum volume valves. Method  2500  proceeds to  2522 . 
     At  2522 , method  2500  reactivates engine cylinders and cylinder valves. The cylinders are reactivated by supplying spark and fuel to the cylinders. The cylinder poppet valves are reactivated by activating valve operators. The valve operators may be part of an assembly as shown in  FIG. 5B , other valve operators described herein, or other known valve operators. Activating the valve operator causes the intake valves to open and close during an engine cycle. Method  2500  proceeds to exit after activating the engine cylinders. 
     At  2508 , method  2500  prepositions engine volumetric efficiency actuators to increase engine volumetric efficiency before engine cylinders and valves are reactivated. The volumetric efficiency actuators are positioned to increase engine volumetric efficiency at the engine&#39;s present speed and driver demand torque as compared to when the volumetric efficiency actuators are adjusted responsive to engine speed and driver demand torque. In one example, cylinder charge motion control valves are fully opened to reduce resistance to flow entering engine cylinders. Further, intake valve timing and exhaust valve timing are adjusted via camshaft timing to provide no intake valve and exhaust valve overlap (e.g., simultaneous opening of intake and exhaust valves). Further, intake valve timing may be advanced or retarded to maximize air in the cylinder at intake valve closing time. The variable plenum volume valve is adjusted to minimize intake manifold volume. The engine throttle is not adjusted when the engine volumetric efficiency actuators are adjusted. Engine boost may also be increased to increase engine volumetric efficiency via closing a turbocharger waste gate or bypass valve. Method  2500  proceeds to  2510  after engine volumetric efficiency actuators are adjusted. 
     At  2510 , method  2500  reactivates engine cylinders and cylinder valves. The cylinders are reactivated by supplying spark and fuel to the cylinders. The cylinder poppet valves are reactivated by activating valve operators. The valve operators may be part of an assembly as shown in  FIG. 5B , other valve operators described herein, or other known valve operators. Activating the valve operator causes the intake valves to open and close during an engine cycle. Method  2500  proceeds to  2512  after activating the engine cylinders. 
     At  2512 , method  2500  judges if the engine intake manifold pressure is at a desired pressure. The desired pressure may be empirically determined and based on engine speed and driver demand torque. If method  2500  judges that engine intake manifold pressure is at the desired engine intake manifold pressure the answer is yes and method  2500  proceeds to  2514 . Otherwise, the answer is no and method  2500  returns to  2512 . 
     At  2514 , method  2500  positions engine volumetric efficiency actuators and the engine throttle based on engine speed and driver demand torque. The positions of the volumetric efficiency actuators may be empirically determined and stored to a table in memory that is indexed via driver demand torque and engine speed. Different tables output different positions for the camshafts, charge motion control valves, and the variable plenum volume valves. Method  2500  proceeds to exit. 
     Referring now to  FIG. 26 , a sequence for operating an engine according to the method of  FIG. 25  is shown. The vertical lines at time T 2600 -T 2405  represent times of interest in the sequence.  FIG. 26  shows six plots and the plots are time aligned and occur at the same time. 
     The first plot from the top of  FIG. 24  is a plot of cylinder deactivation request versus time. The vertical axis represents the cylinder deactivation request. Cylinder deactivation is requested when the cylinder deactivation request trace is at a higher level near the vertical axis arrow. Cylinder deactivation is not requested when the cylinder deactivation request trace is at a lower level near the horizontal axis. The horizontal axis represents time and time increases from the left side of the figure to the right side of the figure. 
     The second plot from the top of  FIG. 26  is a plot of cylinder state versus time. The vertical axis represents the cylinder state. The cylinder is deactivated when the cylinder state trace is at a lower level near the horizontal axis. The cylinder is not deactivated when the cylinder trace is at a higher level near the vertical axis arrow. The horizontal axis represents time and time increases from the left side of the figure to the right side of the figure. 
     The third plot from the top of  FIG. 26  is a plot of engine intake manifold pressure versus time. The vertical axis represents engine intake manifold pressure and engine intake manifold pressure increases in the direction of the vertical axis arrow. The horizontal axis represents time and time increases from the left side of the figure to the right side of the figure. Horizontal line  2602  represents a desired engine intake manifold pressure during deceleration cut out. The level of  2602  may be a same pressure as when the engine is operating at idle speed and no driver demand torque. 
     The fourth plot from the top of  FIG. 26  is a plot of engine volumetric efficiency actuator state versus time. The vertical axis represents engine volumetric efficiency actuator state and the engine volumetric efficiency actuator increases engine volumetric efficiency in the direction of the vertical axis arrow. The engine volumetric efficiency actuator state lowers engine volumetric efficiency when the trace is near the horizontal axis. The horizontal axis represents time and time increases from the left side of the figure to the right side of the figure. 
     The fifth plot from the top of  FIG. 26  is a plot of engine throttle position versus time. The vertical axis represents engine throttle position and the throttle opening amount increases when the trace is closer to the vertical axis arrow. The engine throttle opening amount decreases when the trace is near the horizontal axis. The horizontal axis represents time and time increases from the left side of the figure to the right side of the figure. 
     The sixth plot from the top of  FIG. 26  is a plot of driver demand torque versus time. The vertical axis represents driver demand torque and the driver demand torque increases in the direction of the vertical axis arrow. The driver demand torque decreases when the driver demand torque trace is near the horizontal axis. The horizontal axis represents time and time increases from the left side of the figure to the right side of the figure. 
     At time T 2600 , the cylinder deactivation request is not asserted and the cylinder state is asserted to indicate that engine cylinders are active and combusting air and fuel. The engine intake manifold pressure is at a higher level and the engine throttle position is open more than a middle level. The engine volumetric efficiency actuators (e.g., camshafts, charge motion control valves, and plenum control valve are at a middle position to provide a middle level of engine volumetric efficiency. The driver demand torque is a middle level. 
     At time T 2601 , the cylinder deactivation request is asserted. The cylinder deactivation request is asserted in response to a decrease in driver demand torque and the engine may be in deceleration fuel cut out. The engine throttle position is also decreased in response to the decrease in driver demand torque. The cylinder state transitions to not asserted to indicate engine cylinders are deactivated in response to the cylinder deactivation request. The engine intake manifold pressure decreases in response to closing the throttle. The cylinder intake valves of cylinders are closed after the throttle closes and after an actual total number of cylinder intake events that reduced the intake manifold pressure to desired level  2602 . The cylinder exhaust valves may also be closed (not shown). The engine intake valves are held closed over one or more engine cycles when the cylinders are deactivated. Fuel flow to the cylinders is also deactivated (not shown). The position of engine volumetric efficiency actuators remains unchanged. 
     Between time T 2601  and time T 2602 , engine intake manifold pressure (MAP) increases in response to air leaking into the engine intake manifold. The air is not evacuated from the engine intake manifold since the cylinder intake valves are closed. The cylinder deactivation request remains asserted and the cylinders remain deactivated. The throttle position remains in a fully closed state and the driver demand remains low. 
     At time T 2602 , the position of the engine volumetric efficiency actuators is adjusted to increase engine volumetric efficiency an anticipation of reactivating engine cylinders. The engine volumetric efficiency actuators are not adjusted to positions based on engine speed and driver demand torque. Rather, they are adjusted to positions that increase engine volumetric efficiency beyond positions of engine volumetric efficiency the actuators provide when they are adjusted responsive to engine speed and driver demand torque. In this example, the position of volumetric efficiency actuators is adjusted in response to engine intake manifold pressure exceeding a desired engine intake manifold pressure  2602 . By adjusting volumetric efficiency actuators in response to MAP, undesirable changes in the positions of the volumetric efficiency actuators may be avoided. Engine intake manifold pressure increases from a pressure below  2602  to a pressure greater than  2602 . However, the engine volumetric efficiency actuators may be adjusted a predetermined amount of time after deactivating cylinders or in response to a request to reactivate engine cylinders. As an alternative, the engine volumetric efficiency actuator position may be adjusted to increase engine volumetric efficiency in response to the request for cylinder deactivation. In one example, camshaft timing is advance or retarded to maximize air inducted from the engine intake manifold into engine cylinders (e.g., camshaft timing is adjusted to provide a higher in cylinder pressure at the time of intake valve closing). Further, intake valve opening and exhaust valve opening overlap is adjusted to zero or negative to reduce air flow into the cylinder from the exhaust system (not shown). The engine throttle position and driver demand torque remain unchanged. 
     At time T 2603 , the cylinder deactivation request is transitioned to not asserted in response to an increase in driver demand torque. The cylinder deactivation request may transition to not asserted in response to an increase in driver demand torque or vehicle speed being less than a threshold speed (not shown). Shortly thereafter, the engine cylinders are reactivated (e.g., intake and exhaust valves open and close each engine cycle and spark and fuel are combusted within engine cylinders) as indicated by the cylinder state transitioning to indicate active cylinders. Further, the position of the volumetric efficiency actuators is adjusted to a position based on engine speed and driver demand torque. The throttle position moves in response to the driver demand torque. 
     Between time T 2603  and time T 2604 , the driver demand torque increases and then decreases. The throttle position also increases and decreases in response to the driver demand torque. The engine intake manifold pressure increases and then decreases to below  2602 . 
     At time T 2604 , cylinder deactivation is requested a second time. However, because engine intake manifold pressure is below level  2602 , the position of the volumetric efficiency actuators is not adjusted. The engine cylinders are deactivated (e.g., combustion is inhibited in the cylinders via ceasing fuel flow and spark to the cylinders, cylinder valves are also deactivated so that they are held closed over one or more engine cycles) as indicated by the cylinder state trace transitioning to a lower level. 
     At time T 2605 , the cylinder deactivation request transitions to not asserted in response to vehicle speed less than a threshold (not shown). The engine cylinders are also reactivated as indicated by the cylinder state trace transitioning to a higher level. The engine volumetric efficiency actuator positions are not adjusted responsive to the deactivation request not being asserted because engine intake manifold pressure is less than  2602 . 
     In this way, MAP may be controlled when exiting a cylinder deactivation state to conserve fuel and reduce torque disturbances. The volumetric efficiency actuators are adjusted to increase the amount of air inducted into engine cylinders so that the engine intake manifold pressure is reduced soon after reactivating engine cylinders. 
     Referring now to  FIGS. 27A and 27B , a method for controlling engine torque during cylinder modes is shown. The method of  FIGS. 27A and 27B  may be included in the system described in  FIGS. 1A-6C . The method of  FIGS. 27A and 27B  may be included as executable instructions stored in non-transitory memory. The method of  FIGS. 27A and 27B  may perform in cooperation with system hardware and other methods described herein to transform an operating state of an engine or its components. 
     At  2702 , method  2700  judges if there is a request to decrease an actual total number of active cylinders (e.g., cylinders with valves that open and close during an engine cycle and cylinders that combust air and fuel during the engine cycle). Method  2700  may judge that there is a request to decrease an actual total number of actual cylinders in response to a decrease in driver demand torque, vehicle speed greater than a threshold, and/or other conditions. If method  2700  judges that there is a request to decrease an actual total number of active cylinders, the answer is yes and method  2700  proceeds to  2704 . Otherwise, the answer is no and method  2700  proceeds to  2714 . 
     At  2704 , method  2700  determines a desired lead of volumetric efficiency actuators for decreasing an actual total number of active cylinders. The lead for the volumetric efficiency actuators is an amount of time from when positions of volumetric efficiency actuators are adjusted for decreasing an actual total number of active cylinders to a time when deactivation of cylinders begins. Adjusting the lead time for the volumetric efficiency actuators may smooth engine torque and provide time for volumetric efficiency actuators to reach desired positions before cylinder deactivation begins so that the engine does not provide more or less torque than is desired. In one example, the lead time is empirically determined and stored in memory. Further, the value of lead time stored in memory may be adjusted based on a difference in desired cylinder air charge and actual cylinder air charge during a transition that decreases the total actual number of active cylinders. The lead time value is extracted from memory. Method  2700  proceeds to  2706 . 
     At  2706 , method  2700  prepositions the engine volumetric efficiency actuators including an amount of boost provided by a turbocharger to increase engine volumetric efficiency. For example, boost may be increased, charge motion control valves may be fully opened, intake plenum volume valves are positioned to decrease intake manifold volume, compressor bypass valves may be at least partially closed, and camshaft timing is adjusted to maximize cylinder charge at intake valve closing time. Engine boost may be increased via closing a waste gate or closing the compressor bypass valve. Adjusting the positions of engine volumetric efficiency actuators increases the volumetric efficiency of cylinders that remain active after the actual total number of active cylinders is decreased. Further, the engine&#39;s central throttle is at least partially closed at the same time (e.g., simultaneously) as the previously mentioned engine volumetric efficiency actuators are adjusted. Closing the central throttle maintains the engine air flow rate while engine volumetric efficiency actuators are adjusted to increase engine volumetric efficiency. Method  2700  proceeds to  2708 . 
     At  2708 , selected cylinders are deactivated after the lead time expires. The cylinders are deactivated via holding intake valves of the cylinders closed over one or more engine cycles while the engine rotates. In some examples, exhaust valves of the cylinders being deactivated may also be held closed over one or more engine cycles while the engine rotates. Further, fuel flow and spark are not delivered to cylinders that are being deactivated. While cylinders are being deactivated, the central throttle is snapped open and fuel delivery is increased to active cylinders so that torque produced by active cylinders counters a torque loss due to deactivating cylinders. Method  2700  proceeds to  2710 . 
     At  2710 , method  2700  adjusts spark timing in response to an error between desired engine air flow and actual engine air flow. The desired engine air flow is engine air flow based on driver demand torque at the time of the cylinder deactivation request. The actual engine air flow is air flow that is measured via an air flow sensor. For example, if the actual engine air flow is greater than the desired engine air flow, the engine air flow error is negative and spark timing is retarded to maintain engine torque. If the actual engine air flow is less than the desired engine air flow, the engine air flow error is positive and spark timing is advanced to maintain engine torque. Method  2700  proceeds to  2712 . 
     At  2712 , method  2700  judges if engine volumetric efficiency actuators are at their desired positions. For example, method  2700  judges if actual engine boost is equal to desired engine boost. Further, method  2700  judges if actual camshaft timing is equal to desired camshaft timing. Likewise, method  2700  judge if actual charge motion control valve position is equal to desired charge motion control valve position. Method  2700  may judge that volumetric efficiency actuators are at their desired positions based on output of one or more sensors such as an intake manifold pressure sensor. If the engine volumetric efficiency actuators are at their desired positions, the answer is yes and method  2700  proceeds to  2714 . Otherwise, the answer is no and method  2700  returns to  2706  to provide more time to move the engine volumetric efficiency actuators. 
     At  2714 , method  2700  adjusts the engine central throttle to provide a desired engine torque. The desired engine torque may be based on a driver demand torque. Method  2700  proceeds to  2720 . 
     At  2720 , method  2700  judges if there is a request to increase an actual total number of active cylinders (e.g., cylinders with valve that open and close during an engine cycle and cylinders that combust air and fuel during the engine cycle). Method  2700  may judge that there is a request to increase an actual total number of actual cylinders in response to an increase in driver demand torque, vehicle speed less than a threshold, and/or other conditions. If method  2700  judges that there is a request to increase an actual total number of active cylinders, the answer is yes and method  2700  proceeds to  2722 . Otherwise, the answer is no and method  2700  proceeds to exit. 
     At  2722 , prepositions the engine volumetric efficiency actuators including an amount of boost provided by a turbocharger to decrease engine volumetric efficiency. For example, boost may be decreased, charge motion control valves may be at least partially closed, intake plenum volume valves are positioned to increase intake manifold volume, and camshaft timing is adjusted to reduce cylinder charge at intake valve closing time. Adjusting the positions of engine volumetric efficiency actuators decreases the volumetric efficiency of cylinders that are active before the actual total number of active cylinders is increased. Further, the engine&#39;s central throttle is at least partially opened at the same time (e.g., simultaneously) as the previously mentioned engine volumetric efficiency actuators are adjusted. Opening the central throttle maintains the engine air flow rate while engine volumetric efficiency actuators are adjusted to decrease engine volumetric efficiency. 
     Additionally, in some examples, intake valve and exhaust valve opening time overlap of engine cylinders (e.g., activated and/or cylinders being activated) may be increased in response to turbocharger waste gate position one cylinder cycle before cylinder reactivation. The turbocharger waste gate position may be indicative of exhaust pressure in deactivated cylinders that include exhaust valves that open and close while the cylinder is deactivated. However, in other examples, the amount of overlap may be based on an amount of residual exhaust gas in the cylinder. For example, the amount of overlap may be increased as the residual amount of exhaust gas in the cylinder increases. If the deactivated cylinders include non-deactivating exhaust valves, boost pressure may be decreased less as compared to if the cylinder is configured with deactivating exhaust valves because exhaust density in cylinders with non-deactivating cylinders may be higher for otherwise same conditions because exhaust in cylinders with non-deactivating cylinders may be cooler. Method  2700  proceeds to  2724 . 
     At  2724 , selected cylinders are reactivated. The cylinders are reactivated via opening and closing intake valves of the cylinders over one or more engine cycles while the engine rotates. In some examples, exhaust valves of the cylinders being reactivated may also be opened and closed over one or more engine cycles while the engine rotates. Further, fuel flow and spark are delivered to cylinders that are being reactivated. While cylinders are being reactivated, the central throttle is snapped closed and fuel delivery is decreased to active cylinders so that torque produced by active cylinders counters a torque increase due to reactivating cylinders. Method  2700  proceeds to  2726 . 
     At  2726 , method  2700  adjusts spark timing in response to an error between desired engine air flow and actual engine air flow. The desired engine air flow is engine air flow based on driver demand torque at the time of the cylinder deactivation request. For example, if the actual engine air flow is greater than the desired engine air flow, the engine air flow error is negative and spark timing is retarded to maintain engine torque. If the actual engine air flow is less than the desired engine air flow, the engine air flow error is positive and spark timing is advanced to maintain engine torque. Method  2700  proceeds to  2728 . 
     At  2728 , method  2700  judges if engine volumetric efficiency actuators are at their desired positions. For example, method  2700  judges if actual engine boost is equal to desired engine boost. Further, method  2700  judges if actual camshaft timing is equal to desired camshaft timing. Likewise, method  2700  judge if actual charge motion control valve position is equal to desired charge motion control valve position. Method  2700  may judge that volumetric efficiency actuators are at their desired positions based on output of one or more sensors such as an intake manifold pressure sensor. If the engine volumetric efficiency actuators are at their desired positions, the answer is yes and method  2700  proceeds to  2714 . Otherwise, the answer is no and method  2700  returns to  2706  to provide more time to move the engine volumetric efficiency actuators. 
     At  2730 , method  2700  adjusts the engine central throttle to provide a desired engine torque. The desired engine torque may be based on a driver demand torque. Method  2700  proceeds to exit. 
     In this way, positions of engine volumetric efficiency actuators may be adjusted when increasing and decreasing the actual total number of active cylinders. Moving the volumetric efficiency actuators at the same time the engine central throttle is moved may reduce engine torque disturbances and reduce engine fuel consumption. 
     Referring now to  FIG. 28A , a sequence for operating an engine according to the method of  FIGS. 27A and 27B  is shown. The engine in the sequence is a four cylinder engine having a firing order of 1-3-4-2. The vertical lines at time T 2800 -T 2804  represent times of interest in the sequence.  FIG. 28A  shows five plots and the plots are time aligned and occur at the same time. 
     The first plot from the top of  FIG. 28A  is a plot of a desired number of active engine cylinders (e.g., cylinders with intake and exhaust valves that open and close during an engine cycle and cylinders in which combustion occurs) versus time. The vertical axis represents the desired number of active engine cylinders and the desired number of active cylinders is listed along the vertical axis. The horizontal axis represents time and time increases from the left side of the figure to the right side of the figure. 
     The second plot from the top of  FIG. 28A  is a plot of an actual number of active engine cylinders (e.g., cylinders with intake and exhaust valves that open and close during an engine cycle and cylinders in which combustion occurs) versus time. The vertical axis represents the actual number of active engine cylinders and the actual number of active cylinders is listed along the vertical axis. The horizontal axis represents time and time increases from the left side of the figure to the right side of the figure. 
     The third plot from the top of  FIG. 28A  is a plot of engine volumetric efficiency actuator position (e.g., waste gate position for adjusting engine boost, camshaft position, charge motion control valve position, plenum actuator position) versus time. The vertical axis represents engine volumetric efficiency actuator position and the position of the actuator increases engine volumetric efficiency in the direction of the vertical axis arrow. The position of the actuator decreases engine volumetric efficiency near the horizontal axis. The horizontal axis represents time and time increases from the left side of the figure to the right side of the figure. 
     The fourth plot from the top of  FIG. 28A  is a plot of central throttle position versus time. The vertical axis represents central throttle position and central throttle position increases in the direction of the vertical axis arrow. The horizontal axis represents time and time increases from the left side of the figure to the right side of the figure. 
     The fifth plot from the top of  FIG. 28A  is a plot of spark timing versus time. The vertical axis represents spark timing and spark timing advances in the direction of the vertical axis arrow. The spark timing is retarded near the horizontal axis. The horizontal axis represents time and time increases from the left side of the figure to the right side of the figure. 
     At time T 2800 , the desired actual total number of engine cylinders is four and the actual total number of active cylinders is four. The engine volumetric efficiency actuators are positioned to provide a lower level of volumetric efficiency. For example, a waste gate is opened to reduce boost, cam timing is advanced to reduce cylinder charge, a plenum valve is positioned to increase intake manifold volume, and charge motion control valves are closed to decrease volumetric efficiency. The engine throttle is partially open and spark timing is advanced to a middle level. 
     At time  2801 , the desired actual total number of active cylinders transitions from four to two. The desired actual total number of active cylinders may be reduced in response to a reduction in driver demand torque (not shown) or other conditions. The actual total number of active cylinders remains at a value of four since no cylinders have been deactivated in response to the desired actual total number of active cylinders. The volumetric efficiency actuator position is providing a low level of engine volumetric efficiency and the throttle position is at a middle level. The spark timing is advanced to a middle level. 
     Between time T 2801  and time T 2802 , the volumetric efficiency actuator position is changed to increase engine volumetric efficiency and the throttle begins closing. The desired actual total number of active cylinders and the actual total number of active cylinders remain constant. Spark timing also remains constant. 
     At time T 2802 , spark timing is retarded in response to an error between actual engine air flow being greater than desired engine air flow. Retarding spark timing truncates engine torque so that engine torque may be maintained constant. The volumetric efficiency actuator position continues to change to increase engine volumetric efficiency and the throttle continues closing. The desired actual total number of active cylinders and the actual total number of active cylinders remain constant. 
     At time T 2803 , deactivation of cylinder valves begins. The cylinder valves may be deactivated via valve operators described in  FIG. 5B , other valve operators described herein, or other known valve operators. In one example, valve operators are deactivated to deactivate cylinder intake valves. Cylinder exhaust valves may also be deactivated. The throttle position is increased to open the throttle so that additional air flows into the two cylinders that remain active. By increasing throttle position, intake manifold pressure (MAP) increases, thereby increasing air flow into active engine cylinders. Air flow ceases to deactivated cylinders as the intake valves of the cylinders being deactivated are deactivated and held closed. The spark timing begins to be retarded since the air charge amount of active cylinders increases. The engine volumetric efficiency actuator does not change position and the desired actual total number of active cylinders remains at a value of two. The actual total number of active cylinders also remains at two since engine cylinders have not been deactivated. 
     At time T 2804 , the actual total number of active engine cylinder changes from four to two. The intake valves of two cylinders (e.g., cylinder numbers  2  and  3 ) are deactivated (not shown) and the throttle position remains constant. The spark timing ceases to change and the engine volumetric efficiency actuator does not change position. 
     In this way, positions of volumetric efficiency actuators and the engine throttle may be adjusted prior to deactivating cylinder valves so that less fuel is used during cylinder mode transitions. Further, spark timing may be adjusted responsive to cylinder air charge error instead of in response to a change in engine throttle position so that less spark retard may be used. 
     Referring now to  FIG. 28B , a sequence for operating an engine according to the method of  FIGS. 27A and 27B  is shown. The engine in the sequence is a four cylinder engine having a firing order of 1-3-4-2. The vertical lines at time T 2820 -T 2823  represent times of interest in the sequence.  FIG. 28B  shows five plots and the plots are time aligned and occur at the same time. 
     The first plot from the top of  FIG. 28B  is a plot of a desired number of active engine cylinders (e.g., cylinders with intake and exhaust valves that open and close during an engine cycle and cylinders in which combustion occurs) versus time. The vertical axis represents the desired number of active engine cylinders and the desired number of active cylinders is listed along the vertical axis. The horizontal axis represents time and time increases from the left side of the figure to the right side of the figure. 
     The second plot from the top of  FIG. 28B  is a plot of an actual number of active engine cylinders (e.g., cylinders with intake and exhaust valves that open and close during an engine cycle and cylinders in which combustion occurs) versus time. The vertical axis represents the actual number of active engine cylinders and the actual number of active cylinders is listed along the vertical axis. The horizontal axis represents time and time increases from the left side of the figure to the right side of the figure. 
     The third plot from the top of  FIG. 28B  is a plot of engine volumetric efficiency actuator position (e.g., waste gate position for adjusting engine boost, camshaft position, charge motion control valve position, plenum actuator position) versus time. The vertical axis represents engine volumetric efficiency actuator position and the position of the actuator increases engine volumetric efficiency in the direction of the vertical axis arrow. The position of the actuator decreases engine volumetric efficiency near the horizontal axis. The horizontal axis represents time and time increases from the left side of the figure to the right side of the figure. 
     The fourth plot from the top of  FIG. 28B  is a plot of central throttle position versus time. The vertical axis represents central throttle position and central throttle position increases in the direction of the vertical axis arrow. The horizontal axis represents time and time increases from the left side of the figure to the right side of the figure. 
     The fifth plot from the top of  FIG. 28B  is a plot of spark timing versus time. The vertical axis represents spark timing and spark timing advances in the direction of the vertical axis arrow. The spark timing is retarded near the horizontal axis. The horizontal axis represents time and time increases from the left side of the figure to the right side of the figure. 
     At time T 2820 , the desired actual total number of engine cylinders is two and the actual total number of active cylinders is two. The engine volumetric efficiency actuators are positioned to provide a higher level of volumetric efficiency. For example, a waste gate is closed to increase boost, cam timing is retarded to increase cylinder charge, a plenum valve is positioned to decrease intake manifold volume, and charge motion control valves are opened to increase volumetric efficiency. The engine throttle is partially open and spark timing is advanced to a lower middle level. 
     At time  2821 , the desired actual total number of active cylinders transitions from two to four. The desired actual total number of active cylinders may be increased in response to an increase in driver demand torque (not shown) or other conditions. The actual total number of active cylinders remains at a value of two since no cylinders have been reactivated in response to the desired actual total number of active cylinders. The volumetric efficiency actuator position is providing a higher level of engine volumetric efficiency and the throttle position is at a middle level. The spark timing is advanced to a lower middle level. 
     Between time T 2821  and time T 2822 , the volumetric efficiency actuator position is changed to decrease engine volumetric efficiency and the throttle begins opening. The desired actual total number of active cylinders and the actual total number of active cylinders remain constant. Spark timing is constant. 
     At time T 2822 , reactivation of cylinder valves begins. The cylinder valves may be reactivated via valve operators described in  FIG. 5B , other valve operators described herein, or other known valve operators. In one example, valve operators are reactivated to reactivate cylinder intake valves. Cylinder exhaust valves may also be reactivated. The throttle position is decreased to close the throttle so that less air flows into the two cylinders that are active. By decreasing throttle position, intake manifold pressure (MAP) decreases, thereby decreasing air flow into active engine cylinders. Air flows into reactivating cylinders as the intake valves of the cylinders being reactivated are opened and closed. The spark timing remains begins to be advanced since the air charge amount of active cylinders decreases. The engine volumetric efficiency actuator does not change position and the desired actual total number of active cylinders remains at a value of four. The actual total number of active cylinders remains at two since engine cylinders have not been reactivated. 
     At time T 2823 , the actual total number of active engine cylinder changes from two to four. The intake valves of two cylinders (e.g., cylinder numbers  2  and  3 ) are reactivated (not shown) and the throttle position remains constant. The spark timing ceases to change and the engine volumetric efficiency actuator does not change position. 
     In this way, positions of volumetric efficiency actuators and the engine throttle may be adjusted prior to reactivating cylinder valves so that less fuel is used during cylinder mode transitions. Further, spark timing may be adjusted responsive to cylinder air charge error instead of in response to a change in engine throttle position so that less spark retard may be used. 
     Referring now to  FIG. 29 , a method for controlling engine fuel injection during cylinder reactivation after entering a cylinder deactivation mode is shown. The method of  FIG. 29  may be included in the system described in  FIGS. 1A-6C . The method of  FIG. 29  may be included as executable instructions stored in non-transitory memory. The method of  FIG. 29  may perform in cooperation with system hardware and other methods described herein to transform an operating state of an engine or its components. 
     At  2902 , method  2900  judges if one or more engine cylinders are deactivated (e.g., intake valves held closed over an engine cycle as the engine rotates and no combustion in the deactivated cylinders). In one example, method  2900  may judge that one or more cylinders are deactivated based on a value of a variable stored in memory or output of one or more sensors. If method  2900  judges that one or more engine cylinders is deactivated, the answer is yes and method  2900  proceeds to  2904 . Otherwise, the answer is no and method  2900  proceeds to  2903 . 
     At  2903 , method  2900  operates engine cylinders and valves to provide a desire torque. The desired torque may be based on accelerator pedal position or a controller determined torque. The engine cylinders are activated by supplying fuel to the cylinders. The valves are activated by enabling valve operators. Method  2900  proceeds to exit. 
     At  2904 , method  2900  judges if cylinder reactivation is requested. Cylinder reactivation may be requested in response to an increase in driver demand torque or vehicle speed being less than a threshold speed. If method  2900  judges that cylinder reactivation is requested, the answer is yes and method  2900  proceeds to  2906 . Otherwise, method  2900  proceeds to  2905 . 
     At  2905 , method  2900  maintains the cylinders in a deactivated state. Fuel is not supplied to the cylinders and the cylinder valves remain deactivated. Method  2900  proceeds to exit. 
     At  2906 , method  2900  judges if the engine is operating in a direct fuel injection (DI) only region or if there is a change in requested engine torque that is greater than a threshold. An engine with port and direct fuel injectors may operate only the direct fuel injectors within a first defined engine operating range (e.g., a defined engine speed and torque output range). Likewise, an engine with port and direct fuel injectors may operate only port fuel inject within a second defined engine operating range. Further, in some engine operating ranges, fuel may be supplied to the engine via port and direct fuel injectors. Method determines engine speed and engine torque then determines if the engine is operating in a range where only direct fuel injection is activated. If so, the answer is yes and method  2900  proceeds to  2908 . Otherwise, the answer is no and method  2900  proceeds to  2920 . 
     At  2920 , method  2900  activates one or more deactivated engine cylinders by supplying spark and fuel to the deactivated cylinders. Additionally, valves of the deactivated cylinders that were held closed over one or more engine cycles are activated to open and close over an engine cycle. The fuel is injected to the cylinders via port fuel injectors since the engine is not operating in a direct injection only engine operating region and since the rate of change in requested engine torque is less than the threshold. Method  2900  proceeds to exit after activating one or more deactivated cylinders. 
     At  2908 , method  2900  reactivates one or more engine cylinders via reactivating cylinder valves and supplying fuel and spark to the deactivated cylinders. The engine cylinders are reactivated such that valves that were held closed during one or more engine cycles open and close during one or more engine cycles. Fuel is supplied to the formerly deactivated cylinders by directly injecting fuel to the cylinders. 
     Direct injection offers the opportunity to combust air and fuel in the formerly deactivated cylinders sooner than port injecting fuel because direct fuel injectors can inject fuel during a compression stroke of a cylinder cycle (e.g., later in the cylinder cycle) while a port fuel injector has to inject fuel during an intake stroke of the cylinder cycle or earlier to support combustion during the cylinder cycle. Therefore, if cylinder reactivation is requested after an intake stoke of a cylinder, fuel can be injected during the compression stroke of the cylinder to support combustion in the cylinder during the compression stroke. In this way, direct injection may enable combustion in a deactivated cylinder in less than 180 crankshaft degrees from the crankshaft degree where cylinder activation is requested, whereas it may take more than 180 crankshaft degrees from the crankshaft degree where cylinder activation is requested for port fuel injected fuel injected to a formerly deactivated cylinder to participate in combustion. 
     If the engine is operating in a range where only port fuel is injected to cylinders, except in engine cycles where the cylinders are reactivated, the cylinders may be reactivated by directly injecting fuel into the cylinders for a predetermined number of engine cycles or cylinder intake events. Port fuel injection may be reactivated in the newly reactivated cylinders after the predetermined number of engine cycles or cylinder intake events at which time direct fuel injection to the newly reactivated cylinders ceases. In this way, the formerly deactivated cylinders may start sooner and direct injection to the cylinders may cease after the predetermined number of engine cycles or cylinder intake events so that mixture preparation in the cylinders may improve soon after the cylinders are reactivated. This may be particularly desirable during conditions where the rate of change in requested engine torque is greater than a threshold so that the driver may experience faster torque response to driver demand torque. 
     If the engine is operating in a region where only direct injection is provided to engine cylinders, direct injection is resumed to the deactivated cylinders and the cylinders operate with improved charge cooling. Direct fuel injection may continue in the engine cylinders until engine operating conditions change. Method  2900  proceeds to  2910 . 
     At  2910 , method  2900  judges if it is permissible to port inject fuel or if only direct fuel injection (DI) is desired. Port fuel injection may be started after a predetermined actual total number of cylinder intake events since the request to activate one or more cylinders. The predetermined actual total number of events ensures that fuel is timely injected to formerly deactivated cylinders via direct fuel injection and that fuel mixture preparation improves in a timely manner after deactivated cylinders are reactivated. Alternatively, only direct fuel injection may be desired at the present engine operating conditions. If method  2900  judges that it is permissible to port fuel inject fuel or if only direct fuel injection is desired, the answer is yes and method  2900  proceeds to  2912 . Otherwise, method  2900  returns to  2908 . 
     At  2912 , method  2900  operates direct and port fuel injectors according to a base schedule. The base schedule may be based on engine speed and driver demand torque. Therefore, direct fuel injection may be used to reactivate deactivated at earlier crankshaft angles after the request to activate cylinders, then port fuel injection or port fuel injection and direct fuel injection may replace only directly injecting fuel. Method  2900  proceeds to exit. 
     Referring now to  FIG. 30 , a sequence for operating an engine according to the method of  FIG. 29  is shown. The vertical lines at time T 3000 -T 3002  represent times of interest in the sequence.  FIG. 30  shows three plots and the plots are time aligned and occur at the same time. The SS marks along each plot represent a brake in time. The brake in time may be long or short in duration. Events to the left of the SS marks represent engine operating conditions where fuel is only port injected unless engine cylinders are being reactivated. Events to the right of the SS marks represent engine operating conditions where fuel is only directly injected. The sequence of  FIG. 30  is for a four cylinder engine with a firing order of 1-3-4-2. The three plots are aligned by crankshaft position. 
     Example exhaust valve opening times are indicated by the cross hatched patterns  3002 ,  3012 ,  3023 ,  3028 ,  3051 ,  3056 ,  3064 , and  3069 . Example intake valve opening time are indicated by the hatched patterns  3004 ,  3013 ,  3024 ,  3029 ,  3052 ,  3057 ,  3065 , and  3070 . Start of direct fuel injection events are indicated by nozzles  3006 ,  3053 ,  3058 ,  3062 , and  3066 . Spark events are indicated by the * at  3010 ,  3015 ,  3026 ,  3054 ,  3059 ,  3063 , and  3067 . Start of port fuel injection events are indicated by nozzles at  3008 ,  3014 ,  3021 , and  3025 . 
     The first plot from the top of  FIG. 30  is a plot of engine events versus engine position for cylinder number three. Engine strokes are plotted along the horizontal axis and indicated by the letters I, C, P, and E. I represents intake stroke. C represents compression stroke, P represents power or expansion stroke, and E represents exhaust stroke. Vertical bars separate each engine stroke and represent top-dead-center or bottom-dead-center of piston travel. Port fuel injection windows such as  3001  and  3011  are identified as PFI. Fuel may be injected to a cylinder for a cylinder cycle via port fuel injectors during the port fuel injection window. Port injecting fuel outside of the port fuel injection window delivers fuel into a different cylinder cycle. Direct fuel injection to cylinders may be during intake and compression strokes. 
     The second plot from the top of  FIG. 30  is a plot of engine events versus engine position for cylinder number two. Engine strokes are plotted along the horizontal axis and indicated by the letters I, C, P, and E. I represents intake stroke. C represents compression stroke, P represents power or expansion stroke, and E represents exhaust stroke. Vertical bars separate each engine stroke and represent top-dead-center or bottom-dead-center of piston travel. 
     The third plot is a plot of a cylinder reactivation request state versus engine position. The vertical axis represents cylinder reactivation state and cylinder reactivation is requested when the plot&#39;s trace is near the height of the vertical axis arrow. The cylinder reactivation state is not requesting cylinder reactivation when the plot&#39;s trace is near the horizontal axis. In some examples, the cylinder reactivation request may be replaced by a requested number of active cylinders variable. 
     At time T 3000 , cylinder numbers two and three are deactivated (e.g., fuel is not injected to the cylinders and the intake and exhaust valves of the cylinders are held in a closed state over an engine cycle) and the cylinder reactivation request is not asserted. Consequently, fuel is not injected to cylinder numbers two and three. Further, intake and exhaust valves of cylinder numbers two and three are held closed. Cylinder numbers one and four are combusting air and fuel mixtures (not shown) while the engine rotates. 
     At time T 3001 , a request is made to reactivate engine cylinders as is indicated by the cylinder reactivation request transitioning to a higher level. The cylinder reactivation request occurs half way through port fuel injection (PFI) window  3001  and it may be based on an increase in driver demand torque. Because the port fuel injector has to provide precise smaller fuel amounts and larger fuel amounts, its flow rate is such that it cannot provide enough fuel during port fuel injection window  3001  to provide for a stoichiometric mixture in cylinder number three. Therefore, fuel is directly injected so that combustion may start in cylinder number three as soon as possible after the cylinder reactivation request. Fuel is directly injected after the first intake stroke after time T 3001 . The fuel injected at  3006  is combusted at  3010 . 
     The cylinder reactivation request occurs at the end of port injection window  3020  before deactivated intake and exhaust valves begin operating. Port fuel injection begins at  3021  early in port fuel injection window  3022  so that the port fuel injector of cylinder number two has sufficient time to inject a fuel amount that produces a stoichiometric mixture in cylinder number two. Fuel is not directly injected into cylinder number two because the cylinder reactivation request occurs too late in the compression stroke to directly inject a desired amount of fuel. 
     Fuel is port injected into cylinder number three for a second combustion event in cylinder number three at  3008 . Fuel is port injected early in port fuel injection window  3011  so that a stoichiometric mixture may be provided in cylinder number three. The fuel injected at  3008  is inducted into cylinder number three when the intake valve is open at  3013 . The second combustion event occurs in cylinder number three at  3015 . 
     Fuel is port injected into cylinder number two for a second combustion event in cylinder number two at  3025 . Fuel is port injected early in port fuel injection window  3027  so that a stoichiometric mixture may be provided in cylinder number two. The fuel injected at  3025  is inducted into cylinder number two when the intake valve is open at  3029 . The second combustion event occurs in cylinder number three at  3026 . 
     Cylinder numbers two and three are deactivated a second time between the SS marks and time T 3002 . Fuel is not injected at this time and combustion does not occur in the cylinders. Cylinder numbers one and four combust air and fuel while the engine rotates (not shown). Cylinder reactivation is not requested. 
     At time T 3002 , the cylinder reactivation request is asserted for a second time. The cylinder reactivation request may be asserted in response to an increase in driver demand torque or other conditions. The engine is operating at conditions where only direct fuel injection is scheduled. Because port fuel injection is not scheduled, the first direct injection since the cylinder reactivation request is at  3062 . Fuel is injected during a compression stroke of cylinder number two and it combusts with air that is trapped in the cylinder when cylinder number two was deactivated. The injected fuel is combusted at a first combustion event  3063  since the cylinder reactivation request at T 3002 . However, in some examples, exhaust may be trapped in cylinder number two or air may leak by pistons if cylinder number two is deactivated for an extended period of time. During those conditions, the first direct fuel injection into cylinder number two after the cylinder reactivation request would be at  3066  after fresh air is drawn into cylinder number two. 
     A first direct injection for cylinder number three after time T 3002  occurs at  3053  after intake and exhaust valves are reactivated and opened at  3051  and  3052 . The fuel injected at  3053  is combusted at  3054 . 
     A second direct injection into cylinder number two is performed at  3066 . Fuel injected at  3066  is combusted with air inducted at  3065 . Spark at  3067  initiates the second combustion event in cylinder number two since the cylinder reactivation request at T 3002 . 
     A second direct injection into cylinder number three is performed at  3058 . Fuel injected at  3058  is combusted with air inducted at  3057 . Spark at  3059  initiates the second combustion event in cylinder number three since the cylinder reactivation request at T 3002 . 
     In this way, direct fuel injection may reduce an amount of time to reactivate engine cylinders that have been deactivated. Further, port fuel may be injected after the engine cylinders are reactivated with direct injection to improve mixing in engine cylinders, thereby reducing engine emissions. 
     Referring now to  FIG. 31 , a method for controlling an engine oil pump responsive to cylinder mode is shown. The method of  FIG. 31  may be included in the system described in  FIGS. 1A-6C . The method of  FIG. 31  may be included as executable instructions stored in non-transitory memory. The method of  FIG. 31  may perform in cooperation with system hardware and other methods described herein to transform an operating state of an engine or its components. 
     At  3102 , method  3100  judges if there is a request to switch cylinder intake valves or intake valves and exhaust valves to a deactivated state. The request may be based on the method of  FIG. 22 . If method  3100  judges that there is a request to switch cylinder poppet valves to a deactivated state, the answer is yes and method  3100  proceeds to  3104 . Otherwise, method  3100  proceeds to  3120 . 
     At  3104 , method  3100  determines a minimum oil gallery pressure to deactivate cylinder poppet valves at the present engine operating conditions. In one example, the engine intake and exhaust poppet valves are normally active and are deactivated by supplying pressurized oil to valve operators. The pressurized oil deactivates the intake and exhaust valves so that the intake and exhaust valves are held closed over one or more engine cycles. If the pressure of the oil is reduced, the deactivated valves are reactivated so that they open and close over an engine cycle. 
     The minimum oil pressure to deactivate the cylinder poppet valves may be empirically determined based on parameters such as engine oil temperature and engine speed. The minimum oil pressure to deactivate the cylinder poppet valves may be stored in a table or function in memory that may be indexed via the parameters. Method  3100  indexes the table or function to determine the minimum oil pressure to deactivate cylinder poppet valves at the present engine operating conditions and proceeds to  3106 . 
     At  3106 , method  3100  determines a minimum oil pressure to lubricate the engine at the present engine operating conditions. The minimum oil pressure to lubricate the engine may be empirically determined based on parameters such as engine oil temperature, engine torque, and engine speed. The minimum oil pressure to lubricate the engine may be stored in a table or function in memory that may be indexed via the parameters. Method  3100  indexes the table or function to determine the minimum oil pressure to lubricate the engine at the present engine operating conditions and proceeds to  3108 . 
     At  3108 , method  3100  determines a minimum oil pressure to actuate variable timing camshafts at the present engine operating conditions. The minimum oil pressure to actuate variable timing camshafts may be empirically determined based on parameters such as engine oil temperature, engine torque, and engine speed. The minimum oil pressure to actuate variable timing camshafts may be stored in a table or function in memory that may be indexed via the parameters. Method  3100  indexes the table or function to determine the minimum oil pressure to actuate variable timing camshafts at the present engine operating conditions and proceeds to  3110 . 
     At  3110 , method  3100  determines a maximum oil pressure from the minimum oil pressures determined at  3104 - 3108  and adjusts actuators to provide the same value. For example, if the minimum poppet valve deactivation oil pressure is 100 kPa, the minimum oil pressure to lubricate the engine is 200 kPa, and the minimum oil pressure to adjust camshaft position relative to crankshaft position is 150 kPa, the maximum oil pressure from the minimum oil pressures is 200 kPa. The oil pressure supplied by the oil pump is commanded to 200 kPa. This resultant oil pressure command is the static oil pressure command. The oil pressure may be adjusted via adjusting oil pump displacement, position of a dump valve, or oil flow through cooling jets. Method  3100  proceeds to  3110 . 
     At  3112 , method  3100  commands an increase in oil pressure in an oil gallery leading to cylinder poppet valve operators. The oil pressure may be increased via increasing a pump displacement command, decreasing flow through an oil gallery dump valve, decreasing flow through piston cooling jets, or increasing oil pump speed. The oil pressure command is increased to a value higher than a value to maintain the valves in a closed state so that the valves are deactivated quickly. This increase in oil pressure command is the dynamic command. The dynamic command may be empirically determined and stored in a table or array that is indexed by engine speed and oil temperature. The dynamic command is relatively short in duration and the static command is longer in duration. In this way, the oil pump pressure command may be comprised of a static command and a dynamic command. Additionally, method  3100  may adjust oil pressure output from the oil pump responsive to oil quality. For example, if oil quality is high, oil pump pressure may be reduced based on improved oil lubricating capacity of newer or higher quality oil. Further, method  3100  may not activate cylinder cooling jets at a same time as activating or deactivating cylinders via intake and exhaust valve operators. Method  3100  proceeds to  3114 . 
     At  3114 , method  3100  reduces oil pressure in the oil gallery to the value determined at  3110 , or the static oil pressure command, once it is determined that desired cylinder poppet valves are deactivated. Method  3100  proceeds to  3116 . 
     At  3116 , method  3100  the cylinder poppet valves are moved to the requested state or held in their present state if there is not a request to change the cylinder state. Method  3100  proceeds to exit. 
     At  3120  method  3100  judges if there is a request to switch cylinder intake valves or intake valves and exhaust valves to an activated state. The request may be based on driver demand torque and/or other vehicle operating conditions. If method  3100  judges that there is a request to switch cylinder poppet valves to an activated state, the answer is yes and method  3100  proceeds to  3122 . Otherwise, method  3100  proceeds to  3114 . 
     At  3122 , method  3100  decreases oil pressure in an oil gallery leading to cylinder poppet valve operators. The oil pressure may be decreased via decreasing a pump displacement command, increasing flow through an oil gallery dump valve, increasing flow through piston cooling jets, or decreasing oil pump speed. Method  3100  proceeds to  3114 . 
     Referring now to  FIG. 32 , a sequence for operating an engine according to the method of  FIG. 31  is shown. The vertical lines at time T 3200 -T 3204  represent times of interest in the sequence.  FIG. 32  shows six plots and the plots are time aligned and occur at the same time. 
     The first plot from the top of  FIG. 32  is a plot of a cylinder deactivation request state versus time. The cylinder deactivation request is the basis for activating and deactivating cylinders. Further, cylinder valves may be activated and deactivated based the cylinder deactivation request. The vertical axis represents the cylinder deactivation request and cylinder deactivation is being requested when the trace is at a higher level near the vertical axis arrow. Cylinder deactivation is not requested when the trace is at a lower level near the horizontal axis. The horizontal axis represents time and time increases from the left side of the figure to the right side of the figure. 
     The second plot from the top of  FIG. 32  is a plot of cylinder deactivation state versus time. The vertical axis represents cylinder deactivation state and one or more engine cylinders are deactivated when the deactivation state trace is at a higher level near the vertical axis arrow. Cylinders are not deactivated when the trace is at a lower level near the horizontal axis. Fuel ceases to flow deactivated cylinders and intake and exhaust valves of deactivated cylinders are held closed over one or more engine cycles so that combustion does not occur in deactivated cylinders. The horizontal axis represents time and time increases from the left side of the figure to the right side of the figure. 
     The third plot from the top of  FIG. 32  is a plot of engine oil pump displacement command versus time. 
     The vertical axis represents the engine oil pump displacement command and the value of the engine oil pump displacement command increase in the direction of the vertical axis arrow. The engine oil pump displacement command is the combined values of the static oil pressure command and the dynamic oil pressure command. The horizontal axis represents time and time increases from the left side of the figure to the right side of the figure. 
     The fourth plot from the top of  FIG. 32  is a plot of the static oil pressure demand versus time. The vertical axis represents the static oil pressure demand and the value of the static oil pressure demand increases in the direction of the vertical axis arrow. The horizontal axis represents time and time increases from the left side of the figure to the right side of the figure. 
     The fifth plot from the top of  FIG. 32  is a plot of the dynamic oil pressure command versus time. The vertical axis represents the dynamic oil pressure command and the value of the dynamic oil pressure command increases in the direction of the vertical axis arrow. The horizontal axis represents time and time increases from the left side of the figure to the right side of the figure. 
     The sixth plot from the top of  FIG. 32  is a plot of the engine oil gallery pressure command versus time. The vertical axis represents the engine oil gallery pressure and the value of the engine oil gallery pressure command increases in the direction of the vertical axis arrow. The horizontal axis represents time and time increases from the left side of the figure to the right side of the figure. Horizontal line  3202  represents a minimum oil gallery pressure to hold a deactivated valve in a deactivated state. 
     At time T 3200 , the cylinder deactivation is not requested and cylinders are not deactivated. The static oil pressure command is at a lower level and the oil pump displacement command is at a lower level. The dynamic oil pressure command is zero. The engine oil gallery pressure is at a lower level. 
     At time T 3202 , the cylinder deactivation request is asserted. The cylinder deactivation request may be asserted in response to a decrease in driver demand torque or other vehicle operating condition. The cylinder deactivation state indicates that cylinders are not deactivated. The dynamic oil pressure command is increased in response to the cylinder deactivation request. The static oil pressure command is also increased in response to the cylinder deactivation request. The oil pump displacement command increases in response to the cylinder deactivation request. The oil pump displacement command adjusts oil pump displacement. The oil gallery pressure increases in response to the oil pump displacement command. 
     Alternatively, an oil gallery dump valve may be at least partially closed to increase oil gallery pressure as shown. Further, in some examples, engine cooling jet flow may be reduced to increase oil gallery pressure as shown. Further still, in some examples, oil pump speed is increased to increase oil gallery pressure as shown. 
     At time T 3203 , the cylinder deactivation state transitions to a higher level to indicate that cylinder valves are deactivated and held closed over one or more engine cycles. The cylinder deactivation state may be based on output of one or more sensors (e.g., valve operator sensors, exhaust sensors, or other sensors). The oil pump displacement command is decreasing and the dynamic oil pressure command is decreasing. The static oil pressure command remains at is previous value. The oil gallery pressure levels off at an oil pressure slightly greater than  3202  so that the valves may remain deactivated and oil pump energy consumption may be reduced. 
     At time T 3204 , the cylinder reactivation request is asserted by transitioning the cylinder deactivation state to a lower level. The cylinder reactivation may be made in response to an increase in driver demand torque or other vehicle operating condition. The cylinder deactivation state indicates that cylinders are deactivated. The dynamic oil pressure command is reduced in response to the cylinder reactivation request. The static oil pressure command is also reduced in response to the cylinder reactivation request. The oil pump displacement command decreases in response to the cylinder reactivation request. The oil pump displacement command adjusts oil pump displacement. The oil gallery pressure decreases in response to the oil pump displacement command. 
     Alternatively, an oil gallery dump valve may be at least partially opened to decrease oil gallery pressure as shown. Further, in some examples, engine cooling jet flow may be increased to decrease oil gallery pressure as shown. Further still, in some examples, oil pump speed is decreased to decrease oil gallery pressure as shown. 
     At time T 3204 , the cylinder deactivation state transitions to a lower level to indicate that cylinder valves are reactivated and opened and closed over one or more engine cycles. The cylinder reactivation state may be based on output of one or more sensors (e.g., valve operator sensors, exhaust sensors, or other sensors). The oil pump displacement command is increasing and the dynamic oil pressure command is increasing. The static oil pressure command remains at is previous value. The oil gallery pressure levels off at value that corresponds to a maximum oil pressure of minimum oil pressure to lubricate the engine, minimum oil pressure to actuate camshafts at a desired rate. 
     In this way, cylinder and cylinder valve deactivation may be accelerated while decreasing energy consumed by the oil pump. Further, the cylinder valves may be reactivated quickly by including a dynamic oil pressure control command. 
     Referring now to  FIG. 33 , a method for controlling engine knock responsive to cylinder operating mode is shown. The method of  FIG. 33  may be included in the system described in  FIGS. 1A-6C . The method of  FIG. 33  may be included as executable instructions stored in non-transitory memory. The method of  FIG. 33  may perform in cooperation with system hardware and other methods described herein to transform an operating state of an engine or its components. 
     At  3302 , method  3300  maps or assigns outputs of engine knock sensors to active cylinders. Alternatively, method  3300  may map outputs of engine knock sensors based on a deactivated cylinder map. For example, for a four cylinder engine with a firing order of 1-3-4-2 and engine knock sensors positioned as shown in  FIG. 2A , knock sensors may be mapped according to table 2. 
                         TABLE 2                  Cylinder   Cylinder mode                                             deactivation mode   1   2   3   4   5   6   7               FUEL   1, 2   1, 2   1   2   1   2   1       FUEL AND AIR   1, 2   1, 2   1, 2   1, 2   1, 2   2   1, 2                    
Table 2 includes two cylinder deactivation modes. The first mode is labeled FUEL and it describes a mode where cylinders are deactivated via ceasing to supply fuel to the cylinders while intake and exhaust valves continue to open and close over an engine cycle. The second mode is labeled FUEL AND AIR and it describes a mode where cylinders are deactivated via ceasing to supply fuel to the cylinders while intake and exhaust valves are held in a closed state over an engine cycle.
 
     Cylinder modes are identified as  1 ,  2 ,  3 ,  4 ,  5 ,  6 , and  7 . Changes between the various modes may be based on time the engine operates in a mode, amount of oil in deactivated cylinders, number of engine revolutions in the mode, and other conditions described herein that may lead to mode changes between different cylinder modes. Mode  1  is where cylinders  1 - 4  are active (e.g., combusting air and fuel while valves open and close over an engine cycle) and the engine rotates via torque produced via cylinders  1 - 4 . Mode  2  is where cylinders  1  and  4  are active and the engine rotates via torque produced via cylinders  1  and  4 . Mode  3  is where cylinders  1 ,  4 , and  2  are active and the engine rotates via torque produced via cylinders  1 ,  4 , and  2 . Mode  4  is where cylinders  1 ,  3 , and  4  are active and the engine rotates via torque produced via cylinders  1 ,  3 , and  4 . Mode  5  is where cylinders  3  and  2  are active and the engine rotates via torque produced via cylinders  3  and  2 . Mode  6  is where cylinders  3 ,  4 , and  2  are active and the engine rotates via torque produced via cylinders  3 ,  4 , and  2 . Mode  7  is where cylinders  1 ,  3 , and  2  are active and the engine rotates via torque produced via cylinders  1 ,  3 , and  2 . Alternatively, the cylinder modes may describe cylinders that are deactivated. 
     In this example, the table cells are filled with values 1 and/or 2, but other values may be used. A value of one indicates a knock sensor positioned near cylinder numbers  1  and  2  is selected for sampling and determining engine knock. A value of two indicates a knock sensor positioned near cylinders numbered  3  and  4  is selected for sampling and determining engine knock. For example, when the engine is operating in cylinder mode A with a FUEL cylinder deactivation mode, knock sensors  1  and  2  are selected and sampled for determining engine knock in cylinders  1 - 4 . On the other hand, when the engine is operating in cylinder mode F with a FUEL AND AIR cylinder deactivation mode, knock sensor  2  is the only knock sensor selected and sampled for determining engine knock in cylinders  3 ,  4 , and  2 . 
     Table 2 shows that individual engine knock sensors may be assigned to detect knock in different cylinders for different cylinder modes and different cylinder deactivation modes. One engine knock sensor may provide improved signal to noise in one cylinder mode and one cylinder deactivation mode while a different knock sensor may provide improved signal to noise in the one cylinder mode and a second cylinder deactivation mode. Further, engine knock thresholds may be adjusted responsive to the knock sensor that is providing knock data according to knock sensor assignments. The engine knock sensor or sensors that are assigned to a particular cylinder mode and cylinder deactivation mode are sampled during an engine cycle for indications of knock in active cylinders. An engine knock sensor not assigned to a particular cylinder mode and a cylinder deactivation mode is not sampled or the samples taken for that knock sensor are not used to determined engine knock during an engine cycle. In this way, engine knock sensors may be mapped to improve signal to noise ratios Similar maps may be provided for six and eight cylinder engines. Method  33  proceeds to  3304 . 
     At  3304 , method  3300  determines which engine cylinders are activated and deactivated. In one example, the activated cylinders are determined as described at  1118  of  FIG. 11  which determines if conditions are present for deactivating one or more cylinders. In other examples, active cylinders may be identified values of variables at particular locations in memory. The values of the variables may be revised each time a cylinder is activated or deactivated. For example, a variable in memory may indicate the operating state of cylinder number one. A value of one in the variable may indicate that cylinder number one is active while a value of zero in the variable may indicate that cylinder number one is deactivated. The operating state of each cylinder may be determined in this way. Method  3300  proceeds to  3306 . 
     At  3306 , method  3300  determines which engine cylinders are deactivated by ceasing fuel flow to the cylinders but not ceasing air flow to the cylinders. Method  3300  also determines which cylinders are deactivated by ceasing fuel flow and air flow to the deactivated cylinders. In one example, the controller assigns each cylinder a variable in memory to keep track of the cylinder&#39;s deactivation mode. A cylinder&#39;s deactivation mode is saved in controller memory when the cylinder is deactivated. For example, a value of a variable is 1 when cylinder number one is deactivated by ceasing fuel flow to the deactivated cylinder number one but not ceasing air flow to the deactivated cylinder number one. Conversely, the value of the variable is 0 when the cylinder number one is deactivated by ceasing fuel flow and air flow to the deactivated cylinder number one. A cylinder may be deactivated via any of the methods and systems described herein. The values of the variables may be revised each time a cylinder deactivated. 
     In some examples, a table similar to table 2 may be constructed to output a threshold knock value based on the cylinder mode and cylinder deactivation mode. Values in the table may be empirically determined and stored to the table. The table is indexed via the cylinder mode and the cylinder deactivation mode. The table outputs the threshold knock values that knock sensor outputs are compared against. If knock sensor output exceeds the threshold knock value, knock may be determined. Method  3300  proceeds to  3308 . 
     At  3308 , method  3300  monitors selected knock sensors to determine engine knock. In particular, knock sensors are selected based on the map of knock sensors described at  3302 . The map of knock sensors is indexed via the cylinder mode and the cylinder deactivation mode. The table outputs engine knock sensors that are sampled during an engine cycle for engine knock in the various cylinder modes and cylinder deactivation modes. In one example, the knock sensors are monitored during specific crankshaft angular ranges for detecting knock in activated cylinders. 
     If knock sensor output exceeds a threshold level (e.g., the knock threshold levels described at  3306 ), engine knock is indicated. In some examples, the knock sensor output may be integrated and compared to the threshold level. If the integrated knock sensor output is greater than the threshold, engine knock is indicated. Method  3300  proceeds to  3310 . 
     At  3310 , method  3300  adjusts an actuator in response to the indication of knock. In one example, spark timing is retarded to reduce engine knock. Fuel injection start of injection timing may be retarded to reduce cylinder pressure and engine knock. Alternatively, the amount of fuel injected may be increased. Further, cylinder air charge may be reduced in some instances to reduce the possibility of engine knock. Further still, the ratio of an amount of port fuel injected to an amount of directly injected fuel may be adjusted in response to engine knock. For example, the amount of directly injected fuel may be increased while the amount of port injected fuel may be decreased. Method  3300  proceeds to exit after the actuator is adjusted. 
     Thus, the method of  FIG. 33  provides for a method for operating an engine, comprising: operating the engine with a first group of combusting cylinders in response to a first condition; operating the engine with a second group of combusting cylinders in response to a second condition; adjusting spark timing of a cylinder in response to an indication of knock via a first group of sensors during the first condition; and adjusting spark timing of the cylinder in response to an indication of knock via a second group of sensors during the second condition. The method includes where the first condition is one or more cylinders deactivated via ceasing fuel flow and not air flow to the one or more cylinders. 
     In one example, the method includes where the second condition is one or more cylinders deactivated via ceasing fuel flow and air flow to the one or more cylinders. The method further comprises switching between combusting air and fuel in the first group of combusting cylinders and combusting air and fuel in the second group of combusting cylinders while engine speed and load are substantially constant. The method includes where the first condition is a first group of deactivated cylinders being deactivated for a threshold number of engine rotations. The method also includes where the second condition is a second group of deactivated cylinders being deactivated for a threshold number of engine rotations. 
     The method of  FIG. 33  also provides for a method for operating an engine, comprising: adjusting spark supplied to a cylinder in response to output of a first knock sensor when a first group of cylinders is deactivated via ceasing fuel flow and not air flow to the first group of cylinders; and adjusting spark supplied to the cylinder in response to output of a second knock sensor when the first group of cylinders is deactivated via ceasing fuel flow and air flow to the cylinder. The method further comprises combusting air and fuel in a second group of cylinders in response to a driver demand torque at a first engine speed and load. The method further comprises combusting air and fuel in a third group of cylinders in response to an actual total number of engine revolutions the first group of cylinders is deactivated. The method further comprises adjusting a ratio of direct injection fuel amount to port injection fuel amount of the cylinder in response to output of the first and second knock sensors. 
     In some examples, the method includes where the cylinder is active and combusting air and fuel. The method includes where the second knock sensor is different than the first knock sensor, and where adjusting spark includes adjusting spark timing. The method further comprises adjusting an engine knock threshold responsive to the first knock sensor being a basis for detecting knock in the cylinder. The method further comprises adjusting the engine knock threshold responsive to the second knock sensor being the basis for detecting knock in the cylinder. 
     Referring now to  FIG. 34 , a sequence for operating an engine according to the method of  FIG. 34  is shown. The vertical lines at time T 3400 -T 3407  represent times of interest in the sequence.  FIG. 34  shows six plots and the plots are time aligned and occur at the same time. The sequence of  FIG. 34  represents a sequence for operating a four cylinder engine at a substantially constant speed and driver demand torque (e.g., torque and speed change by less than 5%). 
     The first plot from the top of  FIG. 34  is a plot of spark timing for active cylinders (e.g., cylinders combusting air and fuel) versus time. The vertical axis represents spark timing for active cylinders and spark is more advanced when the trace is at a higher level near the vertical axis arrow. Spark is less advanced or retarded when the trace is at a lower level near the horizontal axis. The horizontal axis represents time and time increases from the left side of the figure to the right side of the figure. 
     The second plot from the top of  FIG. 34  is a plot of active cylinder group versus time. The vertical axis represents active cylinder group and the cylinder group is active when the trace is at the level of the cylinder group. In this example, there are two possible cylinder groups A and B as indicated along the vertical axis. Group  1  indicates cylinders  1 - 4  are active and combusting air and fuel. Group  2  indicates cylinders  1  and  4  are active and combusting air and fuel. Cylinders  2  and  3  are deactivated when group  3  is active. The horizontal axis represents time and time increases from the left side of the figure to the right side of the figure. 
     The third plot from the top of  FIG. 34  is a plot of cylinder deactivation mode versus time. The vertical axis represents the cylinder deactivation mode. Cylinders are not deactivated when the cylinder deactivation trace is near the center of the vertical axis. Deactivated cylinders are deactivated via ceasing to supply air and fuel to the deactivated cylinders when trace is near the vertical axis arrow. Deactivated cylinders are deactivated via ceasing to supply fuel to the deactivated cylinders while air flows through the deactivated cylinders when trace is near the horizontal axis. The horizontal axis represents time and time increases from the left side of the figure to the right side of the figure. 
     The fourth plot from the top of  FIG. 34  is a plot that shows sampled knock sensors versus time. The vertical axis represents the knock sensor being sampled. A value of one indicates that only the first knock sensor is sampled. A value of two indicates that only the second knock sensor is sampled. Values 1 and 2 indicate that both first and second knock sensors are sampled. The horizontal axis represents time and time increases from the left side of the figure to the right side of the figure. 
     The fifth plot from the top of  FIG. 34  is a plot of knock sensor output amplitude versus time. The vertical axis represents knock sensor amplitude and knock sensor output increases in the direction of the vertical axis arrow. Solid line  3404  is output from the first knock sensor. Dashed line  3406  is output from the second knock sensor. The horizontal axis represents time and time increases from the left side of the figure to the right side of the figure. Dashed line  3402  represents a threshold level for comparing knock sensor output. If knock sensor output is greater than  3402 , engine knock is indicated. The level of 3402 is adjusted for cylinder group and cylinder deactivation mode. 
     The sixth plot from the top of  FIG. 34  is a plot of indicated engine knock versus time. The vertical axis represents indicated engine knock. The horizontal axis represents time and time increases from the left side of the figure to the right side of the figure. An engine actuator may be adjusted responsive to indicated engine knock to reduce the possibility of further engine knock. 
     At time T 3400 , cylinder group  1  is active and spark timing is more advanced. Cylinders are not deactivated so the cylinder deactivation mode indicates no deactivated cylinders. The sampled knock sensors are  1  &amp;  2  so that the first and second knock sensors are sampled to determine if engine knock is present. The outputs from the first and second knock sensors is less than threshold  3402  so engine knock is not indicated. 
     At time T 3401 , the active cylinder group switches to group  2 . Two engine cylinders are deactivated under group  2  (e.g., cylinder numbers  2  and  3 ). The active cylinder group may change in response to a decrease in driver demand torque or other changes in vehicle operating conditions (e.g., engine temperature reaching a threshold temperature). Spark timing is retarded to reflect a higher load in the two active cylinders even though driver demand torque has not changed (not shown). The two cylinders are deactivated via deactivating fuel flow cylinders. Fuel injection is stopped to stop fuel flow to the two cylinders. Air continues to flow through the deactivated cylinders since the cylinder deactivation mode is FUEL. The sampled knock sensors remain unchanged. The knock sensor threshold  3402  is reduced to a lower level since background noise may be reduced since two engine cylinders are inactive and combustion noise may be reduced. The outputs of the knock sensors does not exceed threshold  3402  so engine knock is not indicated. 
     At time T 3402 , the active cylinder group switches back to group  1 . The active cylinder group may change state in response to an increase in driver demand torque, a decrease in engine temperature, or another condition. The cylinder deactivation mode switches back to the center value to indicate no cylinders are deactivated. The sampled knock sensors remain unchanged. The knock sensor threshold increases back to its previous level and no engine knock is indicated since the knock sensor outputs are less than threshold  3402 . Engine spark timing returns to its previous value. 
     At time T 3403 , the active cylinder group switches again to group  2 . The two cylinders are deactivated via deactivating fuel and air to the cylinders. Fuel injection is stopped to stop fuel flow to the two cylinders and intake and exhaust valves of the two deactivated cylinders are held closed during an engine cycle to cease air flow to the two deactivated cylinders. The sampled knock sensors remain unchanged. The knock sensor threshold  3402  is reduced to a lowest level since background noise may be reduced by lack of combustion in deactivated cylinders and deactivating cylinder valves since valve impact is reduced. The outputs of the first and second knock sensors does not exceed threshold  3402  so engine knock is not indicated. Spark timing is retarded to reflect the increased load on the active cylinders to maintain the driver demand torque. 
     At time T 3404 , output of the first knock sensor exceeds threshold  3402 . Therefore, engine knock is indicated as shown in the sixth plot. Spark timing is further retarded in response to the indication of engine knock. The active cylinder group remains  2  and cylinder air flow and fuel flow to deactivated cylinders remains stopped. The sampled knock sensors remain unchanged. The knock sensor output decreases in response to the increased spark retard. 
     At time T 3405 , the active cylinder group switches back to group  1 . The cylinder deactivation mode switches back to the center value to indicate no cylinders are deactivated. The sampled knock sensors remain unchanged. The knock sensor threshold increases back to its initial level and no engine knock is indicated since the knock sensor outputs are less than threshold  3402 . 
     At time T 3406 , the active cylinder group switches to group  3 . Three cylinders (e.g., cylinders numbered  1 ,  4 , and  2 ) are active in cylinder group  3 . The sampled knock sensors switches from 1 &amp; 2 to 1. Therefore, the first knock sensor is the only knock sensor sampled when group  3  is activated and cylinders are deactivated via ceasing fuel flow without ceasing air flow to deactivated cylinders (e.g., FUEL as shown in table 2). By switching the knock sensors sampled, the signal to noise ratio for determining engine knock may be improved. Engine knock is not indicated since the first and second knock sensor output is less than threshold  3402 . 
     At time T 3407 , the active cylinder group switches back to group  1 . The cylinder deactivation mode switches back to the center value to indicate no cylinders are deactivated. The knock sensor threshold increases back to its initial level and no engine knock is indicated since the outputs of the first and second knock sensors less than threshold  3402 . 
     In this way, different knock sensors may be sampled in response to the active cylinder group and cylinder deactivation mode. Further, the threshold level that knock sensor outputs are compared to may change in response to cylinder mode and cylinder deactivation mode. The cylinder modes, knock sensors sampled, knock threshold levels, and cylinder groups are exemplary in nature and are not intended to limit the scope or breadth of the disclosure. 
     Referring now to  FIG. 35 , a method for controlling engine knock responsive to cylinder deactivation mode is shown. The method of  FIG. 35  may be included in the system described in  FIGS. 1A-6C . The method of  FIG. 35  may be included as executable instructions stored in non-transitory memory. The method of  FIG. 35  may perform in cooperation with system hardware and other methods described herein to transform an operating state of an engine or its components. 
     At  3502 , method  3500  estimates temperatures of engine cylinders via a model and/or counts an actual total number of engine cycles the deactivated cylinders are deactivated. Temperatures of active and deactivated cylinders are modeled. In one example, a steady state temperature of a cylinder is determined at  3504  via the following equation:
 
CYL ss =Cyl_temp_ fn ( N,L ,Cyl_ d _state)· AF _ fn ( afr )· Spk _ fn ( spkMBT )· EGR _ fn ( EGR )
 
where CYLss is the estimate of steady state cylinder temperature (e.g., temperature of a cylinder); Cyl_temp_fn is cylinder temperature as a function of engine speed (N), engine load (L), and cylinder deactivation state (CYL_d_state); AF_fn is a function that provides a real number multiplier for cylinder air/fuel ratio (afr); Spk_fn a function that provides a real number multiplier for cylinder spark based on spark retard for MBT spark timing (spkMBT); and EGR_fn is a function that provides a real number multiplier for exhaust gas recirculation percentage (EGR). CYL_d_state identifies if the cylinder is active and combusting air and fuel or deactivated and not combusting air and fuel so that the output CYLss changes if the engine cylinder changes from activated to deactivated or vise-versa. The steady state temperature of a cylinder is modified by a time constant to provide the cylinder temperature estimate via the following equation:
 
               CYL   tmp     =         CYL   0     ⁢     e       -   t     τ         +     CYLss   ⁢           ⁢     (     1   -     e       -   t     τ         )               
where CYL imp  is the final estimated cylinder temperature, CYL 0  is the initial cylinder temperature, t is time, and τ is a system time constant. In one example, τ is a function of air flow through the cylinder whose temperature is being estimated and engine temperature. In particular, air flows through the cylinder when fuel flow to the cylinder is deactivated and combustion in the cylinder ceases. The value of τ increases as air flow through the cylinder decreases, and the value of τ decreases as air flow through the cylinder increases. The value of τ decreases as engine temperature increases and the value of τ increases as engine temperature decreases. The value of CYL imp  approaches the value CYLss if the cylinder is not deactivated for a longer duration. Method  3500  proceeds to  3506 .
 
     At  3506 , method  3500  counts an actual total number of engine cycles the one or more cylinders are deactivated and not combusting air and fuel. In one example, a counter counts the actual number of engine cycles the one or more cylinders are deactivated by counting an actual total number of engine revolutions since the one or more cylinders were deactivated and dividing the result by two since there are two engine revolutions in one engine cycle. The actual number of engine revolutions is determined via output of the engine crankshaft position sensor. 
     At  3508 , method  3500  monitors all engine cylinders for knock. All engine cylinders may be monitored for knock via one or more engine knock sensors. Engine knock sensors may include but are not limited to accelerometers, pressure sensors, and acoustic sensors. Knock for individual cylinders may be monitored during predetermined crankshaft angular intervals or windows. Engine knock may be present when output of a knock sensor exceeds a threshold value. Method  3500  proceeds to  3510 . 
     At  3510 , method  3500  reduces the possibility of knock in engine cylinders where knock is indicated. In one example, method  3500  reduces the possibility of engine knock in cylinders where engine knock was indicated at  3508  by retarding spark timing of cylinders where engine knock was indicated. In other examples, start of fuel injection timing may be retarded. Method  3500  proceeds to  3512 . 
     At  3512 , method  3500  advances spark timing of cylinders in which spark timing was retarded to reduce the possibility of engine knock. Spark timing is advanced to improve engine fuel economy, engine emissions, and engine efficiency. Spark timing may be advanced up to a spark timing limit (e.g., minimum spark advance for best engine torque (MBT)) from the retarded spark timing based on a base spark advance gain. 
     A spark advance gain for a cylinder may be based on the cylinder&#39;s temperature estimated at  3504  and/or the counted number of cycles the cylinder was deactivated and the counted number of cylinder cycles the cylinder is activated since the cylinder was deactivated its last time. The base spark advance gain may be added to the retarded spark timing. In one example, the spark advance gain for a cylinder may be expressed as X degrees/second where the value of variable X is based on cylinder temperature. Thus, spark may be advanced from a retarded timing by adding the spark advance gain value to the retarded spark timing. For example, if MBT spark timing is 20 degrees before top-dead-center and the spark timing is retarded to 10 crankshaft degrees before top-dead-center in response to engine knock, the spark advance gain advances spark timing from 10 crankshaft before top-dead-center to 20 crankshaft degrees before top-dead-center in one second, unless engine knock is indicated while advancing spark timing. In other examples, the spark advance gain may be a multiplier that increases or decreases a base spark timing. For example, the spark advance gain may be a real number that varies between 1 and 2 such that if a base spark timing is 10 degrees before top-dead-center, spark timing may be advanced up to 20 degrees before top-dead-center by multiplying the base spark timing by the spark advance gain. In this way, spark timing may be advanced back to MBT spark timing to improve engine emissions, fuel economy, and performance. Method  3500  proceeds to exit. 
     Alternatively, the spark gain may be a function of the counted number of cycles the cylinder was deactivated and the counted number of cylinder cycles the cylinder is activated since the cylinder was deactivated its last time. For example, if the cylinder was deactivated for 10,000 engine cycles and activated for 5 engine cycles before knock was encountered in the cylinder, the spark gain may be a larger value (e.g., 2 deg/second). However, if the cylinder was deactivated for 500 engine cycles and activated for 5 cycles before knock was encountered in the cylinder, the spark gain may be a smaller value (e.g., 1 deg/second). 
     Thus, a rate at which spark may be advanced after retarding spark for engine knock may be adjusted responsive to temperatures of cylinders and/or a number of actual total engine cycles since one or more cylinders were deactivated. Consequently, the rate that spark is advanced may be adjusted to reduce the possibility of engine knock when advancing spark. Yet, spark may be advanced at a rate that improves engine efficiency, economy, and performance. 
     Referring now to  FIG. 36 , a sequence for operating an engine according to the method of  FIG. 35  is shown. The vertical lines at time T 3600 -T 3606  represent times of interest in the sequence.  FIG. 36  shows five plots and the plots are time aligned and occur at the same time. The sequence of  FIG. 36  represents a sequence for operating a four cylinder engine at a constant speed and driver demand torque. 
     The first plot from the top of  FIG. 36  is a plot of cylinder (e.g., a cylinder that is not combusting fuel and air) temperature versus time for operation of the cylinder being illustrated. The vertical axis represents cylinder temperature and cylinder temperature increases in the direction of the vertical axis arrow. The horizontal axis represents time and time increases from the left side of the figure to the right side of the figure. 
     The second plot from the top of  FIG. 36  is a plot of cylinder spark timing versus time for operation of the cylinder being illustrated. The vertical axis represents spark timing of the cylinder and the spark advance increases in the direction of the vertical axis arrow. The horizontal axis represents time and time increases from the left side of the figure to the right side of the figure. 
     The third plot from the top of  FIG. 36  is a plot of cylinder deactivation mode versus time for the cylinder being illustrated. The vertical axis represents the cylinder deactivation mode. The cylinder is not deactivated when the cylinder deactivation trace is near the center of the vertical axis. The cylinder is deactivated via ceasing to supply air and fuel to the cylinder when trace is near the vertical axis arrow. The cylinder is deactivated via ceasing to supply fuel to the cylinder while air flows through the cylinder when trace is near the horizontal axis. The horizontal axis represents time and time increases from the left side of the figure to the right side of the figure. 
     The fourth plot from the top of  FIG. 36  is a plot of cylinder spark advance gain for the illustrated cylinder in crankshaft degrees per second versus time. The vertical axis represents spark advance gain and spark advance gain increases in the direction of the vertical axis arrow. The horizontal axis represents time and time increases from the left side of the figure to the right side of the figure. 
     The fifth plot from the top of  FIG. 36  is a plot of indicated engine knock versus time. The vertical axis represents indication of engine knock and engine knock is indicated when the trace is at a level near the vertical axis arrow. The horizontal axis represents time and time increases from the left side of the figure to the right side of the figure. 
     At time T 3600 , the cylinder temperature is high and cylinder&#39;s spark timing is more advanced. The cylinder is not deactivated as indicated by the cylinder deactivation mode trace being at a middle level. The cylinder&#39;s spark gain is at a lower level and engine knock is not indicated. 
     At time T 3601 , the engine cylinder is deactivated via stopping fuel flow and air flow to the cylinder as indicted by the cylinder deactivation mode trace. Air flow is stopped to the deactivated cylinder by holding intake and exhaust poppet valves of the cylinder closed during an engine cycle. Alternatively, intake valves of the deactivated cylinder may be held closed while exhaust valves of deactivated cylinder open and close during an engine cycle. The temperature of the cylinder begins to decline, but at a lower rate since air is not flowing through the deactivated cylinder. The cylinder spark advance gain remains unchanged while the cylinder is deactivated. Spark timing for the cylinder is not shown since the cylinder is deactivated. Engine knock is not indicated. 
     At time T 3602 , the cylinder is reactivated by supplying fuel and air to the cylinder as indicated by the cylinder deactivation mode trace transitioning to the middle level. The cylinder spark advance gain increases based on the cylinder&#39;s temperature. The cylinder&#39;s spark timing returns to an advance level and the cylinder&#39;s temperature begins increasing. Knock is not indicated. 
     At time T 3603 , engine knock is indicated and the cylinder&#39;s spark timing is retarded to mitigate the engine knock. The cylinder temperature is increasing but at a level less than a long term stable level for the present engine speed and load. The cylinder is active and the cylinder spark advance gain is at an elevated level. 
     Between time T 3603  and time T 3604 , the spark timing for the cylinder is increased using the spark advance gain based on the cylinder&#39;s temperature. Knock in the cylinder is not present as the cylinder&#39;s spark advance increases. The spark advance increases at a predetermined rate (e.g., 10 crankshaft degrees/second) so that engine efficiency, performance, and emission may be improved after cylinder spark timing is retarded in response to engine knock. The cylinder spark advance gain is decreased after the cylinder has been activated and cylinder temperature has increased. 
     At time T 3604 , engine cylinder is deactivated a second time via stopping fuel flow to the cylinder while air continues to flow through the deactivated cylinder as indicted by the cylinder deactivation mode trace. The cylinder temperature is at a level it was at back at time T 3600  and then it begins to decline at a fast rate since air flowing through the cylinder cools the cylinder. Knock in the cylinder is not indicated because the cylinder is deactivated. 
     At time T 3605 , the cylinder is reactivated by supplying spark and fuel to the cylinder. The cylinder may be reactivated in response to an increase in requested engine torque or other operating conditions. The cylinder spark timing is at a more advanced value or timing. The cylinder temperature begins to increase after the cylinder is reactivated. The cylinder spark advance gain is also increased in response to activating the cylinder. Knock is not indicated in the cylinder. 
     At time T 3606 , engine knock is indicated. The cylinder&#39;s temperature is at a lower level and when knock is indicated. Spark timing for the cylinder is retarded in response to knock in the cylinder. The cylinder&#39;s temperature continues to increase. 
     After time T 3606 , the cylinder spark timing is advanced at a predetermined rate (e.g., 15 crankshaft degrees/second) so that engine efficiency, performance, and emission may be improved after active cylinder spark timing is retarded in response to engine knock. The cylinder spark timing increases in a ramp-like fashion and it increases at a faster rate than at time T 3603 . Spark timing may be increased at a faster rate since the cylinder temperature is lower than at time T 3603 . Engine knock is not indicated in the cylinder and the cylinder temperature continues to increase. 
     In this way, engine spark timing may be adjusted responsive to the cylinder deactivation mode and the cylinder spark advance gain. Further, engine knock may be mitigated while degradation of engine performance and emissions is reduced. 
     Referring now to  FIG. 37 , a method for controlling engine knock in the presence of cylinder deactivation is shown. The method of  FIG. 37  may be included in the system described in  FIGS. 1A-6C . The method of  FIG. 37  may be included as executable instructions stored in non-transitory memory. The method of  FIG. 37  may perform in cooperation with system hardware and other methods described herein to transform an operating state of an engine or its components. 
     Referring now to  3702 , method  3700  determines engine knock windows for detecting knock in each engine cylinder. In one example, engine knock detection windows are engine crankshaft intervals where engine knock is expected to occur. For example, if top-dead-center compression stroke for cylinder number one is 0 crankshaft degrees, knock in cylinder number on may be expected in a range of between 20 crankshaft degrees after top-dead-center cylinder number one compression stroke and 50 crankshaft degrees after top-dead-center cylinder number one compression stroke. Thus, the knock detection for cylinder number one is between 20 and 50 crankshaft degrees after top-dead-center cylinder number one compression stroke in this example. Knock detection windows for other engine cylinders may be defined similarly. The engine knock window ranges for each cylinder may be empirically determined and stored in a table or function in controller memory. The table may be indexed via engine speed and engine torque. Method  3700  proceeds to  3704 . 
     At  3704 , method  3700  selectively samples one or more engine knock sensor outputs based on the present engine position and the engine knock windows. For example, method  3700  samples an engine knock sensor in a range of between 20 crankshaft degrees after top-dead-center cylinder number one compression stroke and 50 crankshaft degrees after top-dead-center cylinder number one compression stroke to determine knock sensor output for the knock window of cylinder number one. Method  3700  proceeds to  3706 . 
     At  3706 , method  3700  judges if there is a good signal to noise ratio for the knock sensor output in the latest or present knock sensor window. In one example, method  3700  may base the judgement on predetermined signal to noise ratios stored a table or function in controller memory. The table or function may be indexed according to the present cylinder knock window, engine speed, and engine torque. If method  3700  judges that there is a good signal to noise ratio, the answer is yes and method  3700  proceeds to  3720 . Otherwise, the answer is no and method  3700  proceeds to  3708 . 
     At  3708 , method  3700  judges if one or more engine cylinders are deactivated. In one example, variables in memory contain values that identify deactivated cylinders. For example, a variable that represents the operational state of cylinder number one may have a value of zero if the cylinder is deactivated and a value of one if the cylinder is active and combusting fuel and air. If method  3700  judges that one or more engine cylinders are deactivated, the answer is yes and method  3700  proceeds to  3710 . Otherwise, the answer is no and method  3700  proceeds to  3740 . 
     At  3710 , method  3700  judges if knock sensor output noise in the knock window at the present crankshaft angle (e.g., present knock window), or if, the knock sensor output noise during a knock window in which knock sensor output was just sampled (e.g., present knock window), is influenced by fuel and air based cylinder deactivation of a cylinder. For example, combustion events for eight cylinder engines are only ninety crankshaft degrees apart. Therefore, for an eight cylinder engine with a firing order of 1-3-7-2-6-5-4-8, combustion noise (e.g., valve closing and block vibration induced via combustion pressure) from cylinder number  6  may enter the knock window of cylinder number  5 . If method  3700  is evaluating knock sensor noise in the knock window of cylinder number five, and cylinder number five is deactivated via deactivating fuel flow and air flow to cylinder number five, then method  3700  may judge that fuel and air based cylinder deactivation influences knock sensor noise in the cylinder number five knock window. Note that even though in this example cylinder number five is deactivated, noise in its knock window may be used for processing knock sensor output when cylinder number five is active during conditions of a low signal to noise ratio. 
     Alternatively, if method  3700  is evaluating knock sensor noise in the knock window of cylinder number five, cylinder number six is deactivated via deactivating fuel flow and air flow to cylinder number six, and noise (e.g., noise of exhaust valves closing while intake valves are held closed during a cylinder cycle or noise from compression and expansion in the deactivated cylinder) from cylinder number six enters the knock window of cylinder number five while cylinder number five is active and combusting air and fuel, then method  3700  may judge that fuel and air based cylinder deactivation influences knock sensor noise in the cylinder number five knock window. If method  3700  judges that knock sensor output noise in the knock window at the present crankshaft angle (e.g., present knock window), or if, the knock sensor output noise during a knock window in which knock sensor output was just sampled (e.g., present knock window), is influenced by fuel and air based cylinder deactivation of a cylinder, the answer is yes and method  3700  proceeds to  3742 . Otherwise, the answer is no and method  3700  proceeds to  3712 . 
     At  3712 , method  3700  judges if knock sensor output noise in the knock window at the present crankshaft angle (e.g., present knock window), or if, the knock sensor output noise during a knock window in which knock sensor output was just sampled (e.g., present knock window), is influenced by fuel based cylinder deactivation of a cylinder. For example, if method  3700  is evaluating knock sensor noise in the knock window of cylinder number five, and cylinder number five is deactivated via deactivating fuel flow while air flows to cylinder number five, then method  3700  may judge that fuel based cylinder deactivation influences knock sensor noise (e.g., noise from opening and closing of valves of cylinder numbers five and six and compression and expansion noise from cylinder numbers five and six) in the cylinder number five knock window. 
     Alternatively, if method  3700  is evaluating knock sensor noise in the knock window of cylinder number five, cylinder number six is deactivated via deactivating fuel flow while air flows to cylinder number six, and noise (e.g., noise of exhaust valves closing while intake valves are held closed during a cylinder cycle or noise from compression and expansion in the deactivated cylinder) from cylinder number six enters the knock window of cylinder number five while cylinder number five is active and combusting air and fuel, then method  3700  may judge that fuel based cylinder deactivation influences knock sensor noise in the cylinder number five knock window. If method  3700  judges that knock sensor output noise in the knock window at the present crankshaft angle (e.g., present knock window), or if, the knock sensor output noise during a knock window in which knock sensor output was just sampled (e.g., present knock window), is influenced by fuel based cylinder deactivation of a cylinder, the answer is yes and method  3700  proceeds to  3742 . Otherwise, the answer is no and method  3700  proceeds to  3730 . 
     At  3714 , method  3700  band pass filters output from a knock sensor sampled during the present knock window. The band pass filter may be a first order or higher order filter. An average of the filtered knock sensor data is taken to provide a second knock reference value. In some examples, the second knock reference value may be determined during conditions where knock is expected to not occur. For example, a second knock reference value may be determined when spark timing is retarded three crankshaft degrees before borderline spark timing. Further, second knock reference values may be determined periodically (e.g., once for every  1000  combustion events in a cylinder at a particular engine speed and torque) instead of every engine cycle. Method  3700  proceeds to  3716 . 
     At  3716 , method  3700  processes the knock sensor data taken in the present knock window based on the second knock reference to determine if knock is present in the cylinder in which combustion occurred for the present knock window. In one example, the knock sensor data taken in the present knock window is integrated to provide an integrated knock value. The integrated knock value is then divided by the second knock reference value and the result is compared to a threshold value. If the result is greater than the threshold value, knock is indicated for the cylinder associated with the knock window. Otherwise, knock is not indicated. Knock may be indicated by changing a value of a variable in memory. Method  3700  proceeds to  3718 . 
     At  3718 , method  3700  adjusts an actuator to mitigate engine knock. In one example, spark timing for the cylinder associated with the knock window is retarded. Additionally, or alternatively, air flow to the cylinder associated with the knock window may be reduced via adjusting valve timing. In still other example, an air-fuel ratio of the cylinder associated with the knock window may be enrichened via adjusting timing of a fuel injector. Method  3700  exits after taking actions to mitigate knock. 
     At  3720 , method  3700  judges if one or more engine cylinders are being reactivated. Method  3700  may judge that one or more engine cylinders are being reactivated or are requested to be reactivated based on one or more variables in memory changing state. For example, a variable that represents the operational state of cylinder number one may have a value of zero if the cylinder is deactivated and the value may transition to a value of one if the cylinder is being reactivated. If method  3700  judges that one or more engine cylinders are being reactivated, the answer is yes and method  3700  proceeds to  3722 . Otherwise, the answer is no and method  3700  proceeds to  3724 . 
     At  3722 , method  3700  adjusts one or more knock reference values for the cylinders being reactivated to a predetermined value or values that the knock reference values had just before the cylinders being reactivated were deactivated. The predetermined value may be empirically determined and stored to memory. The values that the knock reference values had just before the cylinders being reactivated were deactivated are stored to memory when cylinder deactivation is requested. Thus, knock reference values for knock windows of each cylinder at various engine speeds and torques are stored to memory in response to cylinder deactivation and the same knock reference values are retrieved from memory in response to activating deactivated cylinders so that the knock reference values are reasonable for activated cylinder conditions instead of using knock reference values determined during cylinder deactivation. Retrieving the knock reference values from memory may improve knock detection when cylinders are reactivated. Method  3700  proceeds to  3724 . 
     At  3724 , method  3700  band pass filters output from a knock sensor sampled during the present knock window. The band pass filter may be a first order or higher order filter. An average of the filtered knock sensor data is taken to provide a third knock reference value. In some examples, the third knock reference value may be determined during conditions where knock is expected to not occur. For example, a third knock reference value may be determined when spark timing is retarded three crankshaft degrees before borderline spark timing. Further, third knock reference values may be determined periodically (e.g., once for every  1000  combustion events in a cylinder at a particular engine speed and torque) instead of every engine cycle. The knock reference value may not be revised to the third reference value until a predetermined amount of time or engine cycles has occurred since cylinder reactivation. Instead, the third knock reference value may be the knock reference value determined at  3722  until the predetermined conditions are met. Method  3700  proceeds to  3726 . 
     At  3726 , method  3700  processes the knock sensor data taken in the present knock window based on the third knock reference to determine if knock is present in the cylinder in which combustion occurred for the present knock window. In one example, the knock sensor data taken in the present knock window is integrated to provide an integrated knock value. The integrated knock value is then divided by the third knock reference value and the result is compared to a threshold value. If the result is greater than the threshold value, knock is indicated for the cylinder associated with the knock window. Otherwise, knock is not indicated. Knock may be indicated by changing a value of a variable in memory. Method  3700  proceeds to  3718 . 
     At  3730  and  3740 , method  3700  band pass filters output from a knock sensor sampled during the present knock window. The band pass filter may be a first order or higher order filter. An average of the filtered knock sensor data is taken to provide a fourth knock reference value. In some examples, the fourth knock reference value may be determined during conditions where knock is expected to not occur. For example, a fourth knock reference value may be determined when spark timing is retarded three crankshaft degrees before borderline spark timing. Further, fourth knock reference values may be determined periodically (e.g., once for every  1000  combustion events in a cylinder at a particular engine speed and torque) instead of every engine cycle. Method  3700  proceeds to  3746 . 
     At  3746 , method  3700  judges if the fourth knock reference value is greater than a threshold. The threshold may be empirically determined and stored to memory. If the further knock reference value is higher than the threshold, the knock intensity value may be lowered because of the way knock intensity is determined. Therefore, to improve the signal to noise ratio of the knock sensor output, the first knock reference value (e.g., determined at  3742 ) or the second knock reference value (e.g., determined at  3714 ) may be selected to process knock sensor data instead of the fourth knock reference value. If method  3700  judges that the fourth knock reference value is greater than the threshold, the answer is yes and method  3700  proceeds to  3750 . Otherwise, the answer is no and method  3700  proceeds to  3748 . 
     At  3748 , method  3700  processes the knock sensor data taken in the present knock window based on the fourth knock reference to determine if knock is present in the cylinder in which combustion occurred for the present knock window. In one example, the knock sensor data taken in the present knock window is integrated to provide an integrated knock value. The integrated knock value is then divided by the fourth knock reference value and the result is compared to a threshold value. If the result is greater than the threshold value, knock is indicated for the cylinder associated with the knock window. Otherwise, knock is not indicated. Knock may be indicated by changing a value of a variable in memory. Method  3700  proceeds to  3718 . 
     At  3750 , method  3700  processes the knock sensor data taken in the present knock window based on the first or second knock reference determined for the present engine speed and torque, but with deactivated cylinders, to determine if knock is present in the cylinder in which combustion occurred for the present knock window. The integrated knock value is then divided by the first or second knock reference value and the result is compared to a threshold value. If the result is greater than the threshold value, knock is indicated for the cylinder associated with the knock window. Otherwise, knock is not indicated. Knock may be indicated by changing a value of a variable in memory. The first knock reference value may be used to determine engine knock during a first condition and the second knock reference may be used to determine engine knock during a second condition. For example, the first knock reference value may be used if engine valve closing noise is greater than a threshold. The second knock reference value may be used if engine value closing noise is less than the threshold. Method  3700  proceeds to  3718 . 
     At  3742 , method  3700  band pass filters output from a knock sensor sampled during the present knock window. The band pass filter may be a first order or higher order filter. An average of the filtered knock sensor data is taken to provide a first knock reference value. In some examples, the first knock reference value may be determined during conditions where knock is expected to not occur. For example, a first knock reference value may be determined when spark timing is retarded three crankshaft degrees before borderline spark timing. Further, first knock reference values may be determined periodically (e.g., once for every  1000  combustion events in a cylinder at a particular engine speed and torque) instead of every engine cycle. Method  3700  proceeds to  3744 . 
     At  3744 , method  3700  processes the knock sensor data taken in the present knock window based on the first knock reference to determine if knock is present in the cylinder in which combustion occurred for the present knock window. In one example, the knock sensor data taken in the present knock window is integrated to provide an integrated knock value. The integrated knock value is then divided by the first knock reference value and the result is compared to a threshold value. If the result is greater than the threshold value, knock is indicated for the cylinder associated with the knock window. Otherwise, knock is not indicated. Knock may be indicated by changing a value of a variable in memory. Method  3700  proceeds to  3718 . 
     Method  3700  may be performed for each engine cylinder as the engine rotates through all the engine cylinder knock windows in an engine cycle. The examples in the description of method  3700  are exemplary in nature and are not intended to limit the disclosure. 
     Additionally, knock control for deactivated cylinders may be suspended by not updating variables and/or adjusting spark timing to deactivated cylinders (e.g., not providing spark to deactivated cylinders). In one example, cylinders that are deactivated are indicated to an engine knock controller so that the knock controller does not have to continue to process knock sensor data for deactivated cylinders. 
     In this way, knock reference values may be adjusted responsive to cylinder deactivation modes and cylinder deactivation to improve signal to noise ratios and engine knock detection. Further, multiple knock reference values may be provided at a particular engine speed and torque based on cylinder deactivation. 
     Referring now to  FIG. 38 , a sequence for operating an engine according to the method of  FIG. 37  is shown. The vertical lines at time T 3800 -T 3804  represent times of interest in the sequence.  FIG. 38  shows three plots and the plots are time aligned and occur at the same time. The sequence of  FIG. 38  represents a sequence for operating a four cylinder engine at a constant speed and driver demand torque. 
     The first plot from the top of  FIG. 38  is a plot of a knock reference value for cylinder number one versus time. The vertical axis represents the knock reference value for cylinder number one and the knock reference value increases in the direction of the vertical axis arrow. A higher knock reference value indicates higher background engine noise (e.g., engine noise not caused by knock in the cylinder being evaluated for knock). The horizontal axis represents time and time increases from the left side of the figure to the right side of the figure. The cylinder number one knock reference value may be based on a first, second, third, or further reference value depending on operating conditions. Horizontal line  3802  represents a threshold level above which the fourth knock reference value may not be selected. 
     The second plot from the top of  FIG. 38  is a plot of a selected knock reference value for cylinder number one versus time. The vertical axis represents the selected knock reference value for cylinder number one and the knock reference value increases in the direction of the vertical axis arrow. The selected knock reference value may be based on a first, second, third, or fourth knock reference value. The four knock reference values are determined as described in  FIG. 37  and the selected knock reference is based on the present vehicle conditions. The selected reference value is the reference value used to process the knock sensor information sampled in the knock window to judge whether or not knock is indicated (e.g., at  3748  of  FIG. 37 ). The horizontal axis represents time and time increases from the left side of the figure to the right side of the figure. 
     The third plot from the top of  FIG. 38  is a plot of cylinder deactivation mode versus time. The vertical axis represents the cylinder deactivation mode. Cylinders are not deactivated when the cylinder deactivation trace is near the center of the vertical axis. Deactivated cylinders are deactivated via ceasing to supply air and fuel to the deactivated cylinders when trace is near the vertical axis arrow. Deactivated cylinders are deactivated via ceasing to supply fuel to the deactivated cylinders while air flows through the deactivated cylinders when trace is near the horizontal axis. The horizontal axis represents time and time increases from the left side of the figure to the right side of the figure. 
     At time  3800 , the cylinder number one knock reference value is a higher middle value less than threshold  3802 . The cylinder number one knock reference value is the third knock reference value (e.g.,  3724  of  FIG. 37 ) because cylinders are not deactivated and the knock sensor signal to noise ratio is low. Engine cylinders are not deactivated as indicated by the deactivated cylinder state being at the middle level. The selected knock reference mode is the value of the cylinder number one knock reference value since the cylinder number one knock reference value is less than threshold  3802 . 
     At time  3801 , the cylinder number one knock reference value changes to a lower value less than threshold  3802 . The cylinder number one knock reference value is the first knock reference value (e.g.,  3742  of  FIG. 37 ) because cylinders are deactivated via fuel and air and because the knock sensor signal to noise ratio is low. Engine cylinders are deactivated via air and fuel (e.g., fuel flow and air flow through cylinder number one is ceased) as indicated by the deactivated cylinder state being at the lower level. The selected knock reference mode is the value of the cylinder number one knock reference value since the cylinder number one knock reference value is less than threshold  3802 . Since cylinders are deactivated at time T 3801 , and since the deactivated cylinder affects noise in the cylinder number one knock window, the cylinder number one reference value is the first knock reference value (e.g., from  3742  of  FIG. 37 ). 
     At time T 3802 , the cylinder number one knock reference value increases in response to reactivating cylinders. The cylinder number one knock reference value is the third knock reference value (e.g.,  3724  of  FIG. 37 ) because it was the value before cylinders were deactivated at time T 3801 . Engine cylinders are reactivated via supplying air and fuel to cylinder number one as indicated by the deactivated cylinder state being at the middle level. The selected knock reference value is adjusted to the cylinder number one knock reference value before cylinders were deactivated at time T 3801 . By using the knock reference value before cylinders were deactivated, an improve knock reference value may be provided since the knock reference value is based on active cylinders (e.g., the current engine operating state) and not deactivated cylinders (e.g., the former engine operating state). 
     At time  3803 , the cylinder number one knock reference value changes to a lower value less than threshold  3802 . The cylinder number one knock reference value is the second knock reference value (e.g.,  3714  of  FIG. 37 ) because cylinders are deactivated via fuel (e.g., fuel injection to the cylinders ceases while air is flowing through the cylinders) and because the knock sensor signal to noise ratio is low. The selected knock reference value is the value of the cylinder number one knock reference value since the cylinder number one knock reference value is less than threshold  3802 . Since cylinders are deactivated at time T 3803 , and since the deactivated cylinder affects noise in the cylinder number one knock window, the cylinder number one reference value is the second knock reference value (e.g., from  3714  of  FIG. 37 ). 
     At time T 3804 , the cylinder number one knock reference value increases in response to reactivating cylinders. The cylinder number one knock reference value is the third knock reference value (e.g.,  3724  of  FIG. 37 ) because it was the value before cylinders were deactivated at time T 3803 . Engine cylinders are reactivated via supplying air and fuel to cylinder number one as indicated by the deactivated cylinder state being at the middle level. The selected knock reference value is adjusted to the cylinder number one knock reference value before cylinders were deactivated at time T 3803 . 
     In this way, the knock reference values of the cylinders that are the basis for determining the presence or absence of engine knock may be adjusted responsive to cylinder deactivation and cylinder deactivation mode. 
     Referring now to  FIG. 39 , a method for performing diagnostics of an engine is shown. The method of  FIG. 39  may be included in the system described in  FIGS. 1A-6C . The method of  FIG. 39  may be included as executable instructions stored in non-transitory memory. The method of  FIG. 39  may perform in cooperation with system hardware and other methods described herein to transform an operating state of an engine or its components. 
     At  3902 , method  3900  monitors the operating states of engine intake and exhaust valves. In one example, the operating states of engine intake and exhaust valves are monitored via pressure sensors in the engine cylinders, engine exhaust system, and/or in the engine intake system (e.g., in the engine intake manifold). Method  3900  proceeds to  3904 . 
     At  3904 , method  3900  judges if cylinder deactivation (e.g., ceasing combustion in the cylinder or cylinders) is requested or if cylinder deactivation is presently underway. Method  3900  may determines which engine cylinders are activated (e.g., combusting air and fuel) and deactivated as described at  1118  of  FIG. 11  or active cylinders may be identified values of variables at particular locations in memory. The values of the variables may be revised each time a cylinder is activated or deactivated. For example, a variable in memory may indicate the operating state of cylinder number one. A value of one in the variable may indicate that cylinder number one is active while a value of zero in the variable may indicate that cylinder number one is deactivated. The operating state of each engine cylinder may be determined in this way. A request to deactivate cylinders may also be based on a value of a variable in memory. Cylinder activation requests and deactivation requests may be commands issued by the controller. If method  3900  judges that one or more cylinders is deactivated or requested deactivated, the answer is yes and method  3900  proceeds to  3906 . Otherwise, the answer is no and method  3500  proceeds to  3930 . 
     At  3906 , method  3900  judges if one or more poppet valves of cylinders requested deactivated are active after commanding the poppet valve deactivated and providing sufficient time to deactivate the cylinders (e.g., one full engine cycle after the request was made). One or more poppet valves may be determined to be active based on cylinder pressure, exhaust pressure, or intake pressure. Alternatively, sensors may be placed on the individual valve operators to determine whether or not valves continue to operate after being commanded deactivated. If method  3900  judges that one or more poppet valves that were commanded deactivated (e.g., held closed as the engine rotates during an engine cycle) continues to operate (e.g., open and close as the engine rotates during the engine cycle), the answer is yes and method  3900  proceeds to  3908 . Otherwise, the answer is no and method  3900  proceeds to  3920 . Note that method  3900  may wait a predetermined amount of time after commanding the one or more poppet valves deactivated before proceeding to  3908  to ensure the poppet valve condition is valid. 
     At  3908 , method  3900  reactivates the cylinder or cylinders in which the poppet valves continue to operate. The cylinder or cylinders are reactivated by activating the cylinder&#39;s poppet valves and supplying fuel and spark to the cylinders. Activating the cylinder poppet valves provides air to the cylinder. The air and fuel are combusted in the activated cylinder. Method  3900  proceeds to  3910 . 
     At  3910 , method  3900  removes the cylinder with one or more valves that did not deactivate from a list of cylinders that may be deactivated. Thus, method  3900  inhibits cylinder deactivation for the cylinder with valves that did not deactivate when the valves were commanded to be deactivated. Method  3900  proceeds to  3912 . 
     At  3912 , method  3900  deactivates an alternative cylinder to provide a desired number of deactivated cylinders. For example, if cylinder number two of a four cylinder engine is requested to be deactivated, but valves of cylinder number two do not deactivate while cylinder numbers one, three, and four are activated, cylinder number two is reactivated as described at  3910  and cylinder number three is commanded deactivated. In this example, the desired number of deactivated cylinders is one and the number of desired active cylinders is three. In this way, the desired number of active and deactivated cylinders may be provided. Consequently, improved fuel economy may be maintained even in the presence of valve operator degradation. Method  3900  proceeds to exit. 
     At  3920 , method  3900  provides a desired amount of engine torque via active cylinders. The desired amount of engine torque may be based on a driver demand torque, and the driver demand torque may be based on a position of an accelerator pedal and vehicle speed. The desired amount of torque from the active cylinders is provided by controlling air flow and fuel flow to the active cylinders. Method  3900  proceeds to exit. 
     At  3930 , method  3900  judges if one or more poppet valves of cylinders requested activated or activated cylinders are deactivated after commanding the poppet valve activated and providing sufficient time to activate the cylinders (e.g., one full engine cycle after the request was made). One or more poppet valves may be determined to be deactivated based on cylinder pressure, exhaust pressure, or intake pressure. Alternatively, sensors may be placed on the individual valve operators to determine whether or not valves do not open and close during an engine cycle after being commanded activated. If method  3900  judges that one or more poppet valves that were commanded activated (e.g., open and close as the engine rotates during an engine cycle) do not open and close during the engine cycle, the answer is yes and method  3900  proceeds to  3932 . Otherwise, the answer is no and method  3900  proceeds to  3940 . Note that method  3900  may wait a predetermined amount of time before proceeding to  3932  after commanding the one or more poppet valves activated to ensure the poppet valve condition is valid. 
     At  3932 , method  3900  deactivates the cylinder or cylinders in which the poppet valves do not open and close during a cylinder cycle. The cylinder or cylinders are deactivated by deactivating the cylinder&#39;s poppet valves and ceasing the supply of fuel and spark to the cylinders. Deactivating the cylinder poppet valves ceases air flow to the cylinder. Method  3900  proceeds to  3934 . 
     At  3934 , method  3900  removes the cylinder with one or more valves that did not activate from a list of cylinders that may be activated. Thus, method  3900  inhibits cylinder activation for the cylinder with valves that did not activate when the valves were commanded to be activated. Combustion is inhibited in cylinders removed from the list of cylinders that may be activated. Method  3900  proceeds to  3936 . 
     At  3936 , method  3900  provides a requested engine torque up to the capacity of cylinders in the list of cylinders that may be activated. The actual total number of cylinders that are active may be increased in response to the engine torque request or decreased in response to the engine torque request. As a result, a significant amount of engine torque may be provided even if poppet valves of one or more cylinders become degraded. Method  3900  proceeds to exit. 
     At  3940 , method  3900  provides a desired amount of engine torque via active cylinders. The desired amount of engine torque may be based on a driver demand torque, and the driver demand torque may be based on a position of an accelerator pedal and vehicle speed. The desired amount of torque from the active cylinders is provided by controlling air flow and fuel flow to the active cylinders. Method  3900  proceeds to exit. 
     Referring now to  FIG. 40 , a sequence for operating an engine according to the method of  FIG. 39  is shown. The vertical lines at time T 4000 -T 4005  represent times of interest in the sequence.  FIG. 40  shows five plots and the plots are time aligned and occur at the same time. The SS along the time line of each plot indicates a break in the sequence. The time between the break may be long or short. The sequence of  FIG. 40  represents a sequence for operating a four cylinder engine with a firing order of 1-3-4-2. 
     The first plot from the top of  FIG. 40  is a plot of cylinder deactivation request (e.g., a request to cease combustion in one or more cylinders) versus time. The vertical axis represents the cylinder deactivation request and cylinder deactivation is requested when the trace it at a level near the vertical axis arrow. The horizontal axis represents time and time increases from the left side of the figure to the right side of the figure. 
     The second plot from the top of  FIG. 40  is a plot of cylinder number two valve operating state versus time. Cylinder valves in cylinder number two are active when the trace is at a higher level near the vertical axis arrow. Cylinder valves in cylinder number two are inactive when the trace is at a lower level near the horizontal axis. The horizontal axis represents time and time increases from the left side of the figure to the right side of the figure. 
     The third plot from the top of  FIG. 40  is a plot of cylinder number three valve operating state versus time. Cylinder valves in cylinder number three are active when the trace is at a higher level near the vertical axis arrow. Cylinder valves in cylinder number three are inactive when the trace is at a lower level near the horizontal axis. The horizontal axis represents time and time increases from the left side of the figure to the right side of the figure. 
     The fourth plot from the top of  FIG. 40  is a plot of an actual total number of requested active cylinders versus time. The vertical axis represents the actual total number of requested active cylinders and the actual total number of requested active cylinders is posted along the vertical axis. The horizontal axis represents time and time increases from the left side of the figure to the right side of the figure. 
     The fifth plot from the top of  FIG. 40  is a plot of requested engine torque versus time. The vertical axis represents requested engine torque and the value of the requested engine torque increases in the direction of the vertical axis arrow. The horizontal axis represents time and time increases from the left side of the figure to the right side of the figure. 
     At time T 4000 , cylinders are not requested deactivated as indicated by the cylinder deactivation request being at a lower level. Valves of cylinder number two and three are active. The valves of cylinder numbers two and three are active based on the number of requested active (e.g., combusting air and fuel) cylinders being four. The requested engine torque is at a higher level. 
     At time  4001 , the requested engine torque decreases. The requested engine torque may decrease in response to a decrease in driver demand torque. The number of requested engine cylinders is decreased from four to three in response to the requested engine torque decrease. Further, the cylinder deactivation request is asserted in response to the decrease in requested engine torque. Cylinder number two is requested deactivated and cylinder poppet valves of cylinder number two are commanded closed. However, the valves of cylinder number two remain active as indicated by the cylinder number two valve state. Because the poppet valves of cylinder number two remained active (e.g., opening and closing as the engine rotates through an engine cycle), cylinder number two is commanded reactivated as indicated by the number of requested active cylinders transitioning back to four. Shortly thereafter, cylinder number three is commanded deactivated in response to the number of active cylinders changing back to three. The poppet valves of cylinder number three become inactive (e.g., are held closed during the engine cycle) and the requested number of active cylinders remains constant at a value of three. 
     At time T 4002 , the requested engine torque increases and the number of requested active cylinders is increased back to four. Cylinder number three is reactivated and the valves of cylinder number three are activated as indicated by the cylinder number three valve state. Cylinder number two remains active and the cylinder deactivation request is not asserted in response to the number of requested active cylinders. 
     At time T 4003 , the cylinder deactivation request is asserted in response to the number of requested active cylinders being two. The valves of cylinder number two and cylinder number three are inactive. The requested engine torque is at a low level that allows the engine to provide the requested torque will less than its full complement of cylinders being active. 
     At time  4004 , the engine torque request increases in response to an increase in driver demand torque (not shown). The number of requested active cylinders increases to a value of four in response to the increased requested torque. Valves of cylinder number three reactivate, but valves of cylinder number two do not reactivate in response to the number of requested active cylinders. Shortly after time T 4004 , the number of requested active cylinders transitions to a value of three and cylinder number two is commanded deactivated (e.g., cease delivery of fuel and hold poppet valves closed during an engine cycle). Further, the cylinder deactivation request is asserted again for cylinder number two. The engine provides as much of the requested torque as the torque capacity of the three active cylinders permits. 
     At time  4005 , the requested engine torque is decreased in response to a decrease in driver demand torque. The number of requested active cylinders is decreased from three to two in response to the decrease in requested engine torque. The valves of cylinder number three are deactivated and cylinder numbers two and three are deactivated in response to the number of requested active cylinders. The cylinder deactivation request is also remains asserted. 
     In this way, the number of requested active engine cylinders may be adjusted responsive to valves that may not be deactivated when they are requested deactivated. Further, the number of requested active engine cylinders may be adjusted responsive to valves that may be deactivate when they are requested activated. 
     Referring now to  FIG. 41 , a method for sampling oxygen sensors of an engine with cylinder deactivation is shown. The method of  FIG. 41  may be included in the system described in  FIGS. 1A-6C . The method of  FIG. 41  may be included as executable instructions stored in non-transitory memory. The method of  FIG. 41  may perform in cooperation with system hardware and other methods described herein to transform an operating state of an engine or its components. 
     At  4102 , method  4100  judges if one or more cylinders of the engine are deactivated. Method  4100  may evaluate a value of a variable stored in memory to determine if one or more engine cylinders are deactivated. If method  4100  judges that one or more engine cylinders are deactivated, the answer is yes and method  4100  proceeds to  4104 . Otherwise, the answer is no and method  4100  proceeds to  4120 . 
     At  4120 , method  4100  samples an oxygen sensor of a cylinder bank twice per exhaust stroke of each cylinder on the cylinder bank. Thus, if the engine is a four cylinder engine with a single bank of cylinders, method  4100  samples the exhaust sensor eight times in two engine revolutions. The samples are then averaged to provide an air-fuel ratio estimate for the engine. Additionally, cylinder specific air-fuel ratios may be estimated via averaging the two samples taken during a cylinder&#39;s exhaust stroke to determine the cylinder&#39;s air-fuel ratio. Method  4100  proceeds to  4108 . 
     At  4108 , method  4100  adjusts fuel supplied to engine cylinders based on the oxygen sensor samples. If the oxygen sensor indicates a leaner air-fuel ratio than is desired, additional fuel may be injected to the engine. If the oxygen sensor indicates a richer air-fuel ratio than is desired, less fuel may be injected to the engine. Method  4100  proceeds to exit. 
     At  4104 , method  4100  determines which engine cylinders are deactivated. In one example, method  4100  evaluates values stored in memory that indicate active and deactivated cylinders. Method  4100  determines which cylinders are deactivated and proceeds to  4106 . 
     At  4106 , method  4100  samples an oxygen sensor of a cylinder bank twice per exhaust stroke of each cylinder on the cylinder bank, except for exhaust strokes of deactivated cylinders which are not sampled. Alternatively, oxygen samples taken during exhaust strokes of deactivated cylinders may be discarded. The samples are then averaged to determine an average engine air-fuel ratio. Method  4100  proceeds to  4108 . 
     By not sampling oxygen sensors during exhaust strokes of deactivated cylinders, it may be possible to reduce air-fuel ratio bias that may be induced on an engine air-fuel estimate. In particular, if one cylinder air-fuel mixture is leaner or richer than other cylinders and its exhaust gases are expelled near an exhaust stroke of a deactivated cylinder, bias to the engine air-fuel ratio may be reduced by not sampling output from the cylinder that is leaner or richer twice during an engine cycle. 
     Referring now to  FIG. 42 , a method for sampling cam sensors of an engine with cylinder deactivation is shown. The method of  FIG. 42  may be included in the system described in  FIGS. 1A-6C . The method of  FIG. 42  may be included as executable instructions stored in non-transitory memory. The method of  FIG. 42  may perform in cooperation with system hardware and other methods described herein to transform an operating state of an engine or its components. 
     At  4202 , method  4200  judges if one or more cylinders of the engine are deactivated. Method  4200  may evaluate a value of a variable stored in memory to determine if one or more engine cylinders are deactivated. If method  4200  judges that one or more cylinders are deactivated, the answer is yes and method  4200  proceeds to  4204 . Otherwise, the answer is no and method  4200  proceeds to  4220 . 
     At  4220 , method  4200  samples an intake cam sensor twice per intake stroke of each cylinder on a cylinder bank that includes an intake cam monitored by the intake cam sensor. Likewise, method  4200  samples an exhaust cam sensor twice per exhaust stroke of each cylinder on a cylinder bank that includes an exhaust cam monitored by the exhaust cam sensor. Thus, if the engine is a four cylinder engine with a single intake cam, method  4200  samples the cam sensor eight times in two engine revolutions. Cam position and speed may be determined for each cam sensor sample taken. Method  4200  proceeds to  4208 . 
     At  4208 , method  4200  adjusts a cam phase actuator command to adjust cam position based on the cam sensor samples. If the cam sensor indicates cam position is not at its desired position and/or if the cam is moving slower or faster than is desired, the cam phase command is adjusted to reduce the error between the actual cam position and the desired cam position. Method  4200  proceeds to exit. 
     At  4204 , method  4200  determines which engine cylinders are deactivated. In one example, method  4200  evaluates values stored in memory that indicate active and deactivated cylinders. Method  4200  determines which cylinders are deactivated and proceeds to  4206 . 
     At  4206 , method  4200  samples a cam sensor of a cylinder bank twice per intake stroke for an intake cam or twice for each exhaust stroke for an exhaust cam, except for exhaust strokes of deactivated cylinders which are not sampled. Alternatively, cam sensor samples taken during intake or exhaust strokes of deactivated cylinders may be discarded. The samples are then processed to determine cam position and speed. Additionally, cam samples may be averaged to reduce cam signal noise. Method  4200  proceeds to  4208 . 
     By not sampling cam sensors during intake or exhaust strokes of deactivated cylinders, it may be possible to reduce cam position bias that may be induced on engine cam position. The rate a cam phase actuator moves may be affected by whether or not a cylinder is deactivated. Therefore, it may be desirable to eliminate cam samples taken when valve springs of deactivated cylinders are not assisting cam movement relative to crankshaft position. 
     Note that the example control and estimation routines included herein can be used with various engine and/or vehicle system configurations. The control methods and routines disclosed herein may be stored as executable instructions in non-transitory memory and may be carried out by the control system including the controller in combination with the various sensors, actuators, and other engine hardware. The specific routines described herein may represent one or more of any number of processing strategies such as event-driven, interrupt-driven, multi-tasking, multi-threading, and the like. As such, various actions, operations, and/or functions illustrated may be performed in the sequence illustrated, in parallel, or in some cases omitted. Likewise, the order of processing is not necessarily required to achieve the features and advantages of the example embodiments described herein, but is provided for ease of illustration and description. One or more of the illustrated actions, operations and/or functions may be repeatedly performed depending on the particular strategy being used. Further, at least a portion of the described actions, operations and/or functions may graphically represent code to be programmed into non-transitory memory of the computer readable storage medium in the control system. The control actions may also transform the operating state of one or more sensors or actuators in the physical world when the described actions are carried out by executing the instructions in a system including the various engine hardware components in combination with one or more controllers. 
     This concludes the description. The reading of it by those skilled in the art would bring to mind many alterations and modifications without departing from the spirit and the scope of the description. For example, I3, I4, I5, V6, V8, V10, and V12 engines operating in natural gas, gasoline, diesel, or alternative fuel configurations could use the present description to advantage.