Patent Publication Number: US-10316773-B2

Title: Methods and system mitigating port injection degradation

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     The present application claims priority to U.S. Provisional Patent Application No. 62/174,292, entitled “Methods and System Mitigating Port Injection Degradation,” filed on Jun. 11, 2015, the entire contents of which are hereby incorporated by reference for all purposes. 
    
    
     FIELD 
     The present description relates to methods and a system for port and direct injection of fuel to an internal combustion engine. The methods and systems may be particularly useful for operating an engine in the presence of port fuel injector degradation. 
     BACKGROUND/SUMMARY 
     An engine cylinder may receive fuel via a port fuel injector and a direct fuel injector. The port fuel injector may supply fuel to a cylinder during times when an intake valve of the cylinder receiving the fuel is open or closed. If the intake fuel is closed when the port fuel injector is activated, the port injected fuel will be inducted to the cylinder during a next open intake valve interval. Direct fuel injectors may supply fuel to a cylinder during an intake stroke or a compression stroke for a combustion event in the compression stroke. By port injecting fuel and directly injecting fuel to a cylinder during a cylinder cycle, the port injected fuel can increase an amount of fuel provided to the cylinder so that the cylinder may operate at higher loads while the direct fuel injector provides charge cooling to reduce the possibility of engine knock. However, if a port fuel injector becomes degraded, the engine cylinder with the degraded port injector may not operate in a same way as engine cylinders where port and direct injector are operating as is desired. 
     The inventors herein have recognized the above-mentioned disadvantages and have developed an engine fueling method, comprising: receiving inputs to a controller; and deactivating all port fuel injectors of an engine in response to reduced performance of a sole port fuel injector based on the inputs to the controller. 
     By deactivating all port fuel injectors of an engine in response to degradation or reduced performance of a single sole port fuel injector, it may be possible to provide the technical result of operating an engine with cylinders that preform substantially the same even in the presence of port fuel injector degradation. In particular, deactivating all port fuel injectors of an engine provides similar operating conditions for all engine cylinders so that no one cylinder may perform differently than other cylinders. Consequently, all active engine cylinders may provide similar levels of torque output and emissions. Further, because the engine cylinders are restricted to a single type of injector, all engine cylinders may be controlled via a simplified strategy that does not require some cylinders to be controlled one way and other cylinders to be controlled a different way. 
     The present description may provide several advantages. For example, the approach simplifies engine control strategy during period of degradation. In addition, the approach may provide for more uniform cylinder operating and output. Further, the approach provides a repeatable procedure for mitigating the effects of port fuel injector degradation. 
     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 FIGURES 
         FIG. 1A  shows a schematic depiction of an engine; 
         FIG. 1B  shows an example of a paired fuel injector driver; 
         FIG. 2  shows a method for providing air and fuel to an engine that includes two different types of fuel injectors; 
         FIG. 3  shows a cylinder timing diagram that includes a longer port fuel injection window duration; 
         FIG. 4  shows an example method for injecting fuel to an engine with constraints that are based on a longer port fuel injection window duration; 
         FIG. 5  shows a cylinder timing diagram that includes a shorter port fuel injection window duration; 
         FIG. 6  shows an example method for injecting fuel to an engine with constraints that are based on a shorter port fuel injection window duration; 
         FIG. 7  shows a method for providing different size port fuel injection windows based on port fuel injection pulse width duration and transitioning between the different size port fuel injection windows; 
         FIG. 8  shows a sequence based on the method of  FIG. 7  where a fuel injection system is transitioned between a shorter duration port fuel injection window and a longer duration port fuel injection window; 
         FIG. 9  shows an example method for adjusting fractions of port injected fuel and direct injected fuel to reduce particulate matter production; 
         FIG. 10  shows an example operating sequence according to the method of  FIG. 9 ; 
         FIG. 11  shows an example method for compensating for port fuel injector degradation; 
         FIG. 12  shows an example operating sequence according to the method of  FIG. 11 ; 
         FIG. 13  shows an example method for compensating for direct fuel injector degradation; and 
         FIG. 14  shows an example operating sequence according to the method of  FIG. 13 . 
     
    
    
     DETAILED DESCRIPTION 
     The present description is directed to supplying fuel to an engine that includes both port and direct fuel injectors.  FIG. 1A  shows one example of a system that includes port and direct fuel injectors. The system includes a spark ignition engine that may be operated with gasoline, alcohol, or a mixture of gasoline and alcohol. The system of  FIG. 1A  may include a paired fuel injector driver as is shown in  FIG. 1B .  FIG. 2  shows a method for supplying fuel to an engine that includes port and direct fuel injectors.  FIG. 3  shows an example cylinder cycle timing diagram that includes a longer port fuel injection window. The method of  FIG. 4  describes port and direct fuel injection for longer port fuel injection windows.  FIG. 5  shows an example cylinder cycle timing diagram that includes a shorter port fuel injection window. The method of  FIG. 6  describes port and direct fuel injection for shorter port fuel injection windows.  FIG. 7  shows a method for operating an engine with different duration port fuel injection windows and transitioning between shorter and longer duration fuel injection windows. A prophetic sequence for changing between shorter and longer duration port fuel injection windows is shown in  FIG. 8 . 
     The present description also provides for controlling an engine responsive to particulate matter accumulation and formation. In particular, a method for adjusting port and direct fuel fractions responsive to particulate matter accumulation and formation is shown in  FIG. 9 . A prophetic sequence for adjusting port and direct injection fractions according to particulate matter formation and accumulation is shown in  FIG. 10 . 
     The present description also provides for controlling an engine responsive to fuel injector degradation. For example, a method for operating an engine with port fuel injector degradation is shown in  FIG. 11 . A prophetic engine operating sequence for an engine exhibiting port fuel injector degradation is shown in  FIG. 12 . A method for operating an engine with direct fuel injector degradation is shown in  FIG. 13 . A prophetic engine operating sequence for an engine exhibiting direct fuel injector degradation is shown in  FIG. 14 . 
     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  includes combustion chamber  30  and cylinder walls  32  with piston  36  positioned therein and connected to crankshaft  40 . 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 cam  51  and an exhaust cam  53 . Alternatively, one or more of the intake and exhaust valves may be operated by an electromechanically controlled valve coil and armature assembly. The position of intake cam  51  may be determined by intake cam sensor  55 . The position of exhaust cam  53  may be determined by exhaust cam sensor  57 . 
     Direct fuel injector  66  is shown positioned to inject fuel directly into cylinder  30 , which is known to those skilled in the art as direct fuel injection or direct injection. Port fuel injector  67  is positioned to inject fuel to cylinder port  13 , which is known to those skilled in the art as port fuel injection or port injection. Fuel injectors  66  and  67  deliver liquid fuel in proportion to the pulse width of signals 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). Fuel injects  66  and  67  may inject a same type of fuel or different types of fuel. In addition, intake manifold  44  is shown communicating with optional electronic throttle  62  which adjusts a position of throttle plate  64  to control air flow from intake boost chamber  46 . 
     Exhaust gases spin turbine  164  which is coupled to compressor  162  via shaft  161 . Compressor  162  draws air from air intake  42  to supply boost chamber  46 . Thus, air pressure in intake manifold  44  may be elevated to a pressure greater than atmospheric pressure. Consequently, engine  10  may output more power than a normally aspirated engine. 
     Distributorless ignition system  88  provides an ignition spark to combustion chamber  30  via spark plug  92  in response to controller  12 . Ignition system  88  may provide a single or multiple sparks to each cylinder during each cylinder cycle. Further, the timing of spark provided via ignition system  88  may be advanced or retarded relative to crankshaft timing in response to engine operating conditions. 
     Universal Exhaust Gas Oxygen (UEGO) sensor  126  is shown coupled to exhaust manifold  48  upstream of exhaust gas after treatment device  70 . Alternatively, a two-state exhaust gas oxygen sensor may be substituted for UEGO sensor  126 . The exhaust system also contains a universal oxygen sensor  127  position downstream of after treatment device  70  in a direction of flow through engine  10 . In some examples, exhaust gas after treatment device  70  is a particulate filter that includes a three-way catalyst. In other examples, the particulate filter may be separate from the three-way catalyst. 
     Controller  12  is shown in  FIG. 1A  as a conventional microcomputer including: microprocessor unit  102 , input/output ports  104 , read-only or non-transitory memory  106 , 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 from temperature sensor  112  coupled to cooling sleeve  114 ; a position sensor  134  coupled to an accelerator pedal  130  for sensing accelerator position adjusted by foot  132 ; a knock sensor for determining ignition of end gases (not shown); a measurement of engine manifold pressure (MAP) from pressure sensor  121  coupled to intake manifold  44 ; a measurement of boost pressure from pressure sensor  122  coupled to boost chamber  46 ; 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  (e.g., a hot wire air flow meter); vehicle environmental information from sensors  90 ; and a measurement of throttle position from sensor  58 . 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. 
     In some embodiments, the engine may be coupled to an electric motor/battery system in a hybrid vehicle. The hybrid vehicle may have a parallel configuration, series configuration, or variation or combinations thereof. Further, in some embodiments, other engine configurations may be employed, for example a diesel engine. 
     Environmental information may be provided to controller  12  via a global positioning receiver, camera, laser, radar, pressure sensors, or other known sensor via sensors  90 . The environmental information may be the basis for adjusting port and direct fuel injection windows and timing as discussed in further detail in the description of  FIG. 9 . 
     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. 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 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 (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 described 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. 
     Referring now to  FIG. 1B , an example of a paired fuel injector driver is shown. Paired fuel injector driver  65  selectively supplies current to fuel injectors  66 . In one example, paired fuel injector driver  65  may be comprised of metal oxide semiconductor field effect transistors (MOSFET). Paired fuel injector driver may include monitoring circuits  69  for sending diagnostic information to controller  12 . Because paired fuel injector driver  65  supplies electric current to two fuel injectors, it may be possible for paired fuel injector driver  65  to degrade, thereby degrading performance of two fuel injectors  66  simultaneously. 
     Thus, the system of  FIGS. 1A and 1B  provide for a system, comprising: an engine including a plurality of cylinders, a plurality of port fuel injectors directed to inject fuel to the plurality of cylinders, and a plurality of direct fuel injectors protruding into the plurality of cylinders; a controller including executable instructions stored in non-transitory memory for deactivating the plurality of port fuel injectors in response to reduced performance of a sole port fuel injector. The system further comprises additional instructions to determine reduced performance of the sole port fuel injector in response to output of an oxygen sensor. The system further comprises additional instructions to deactivate a direct fuel injector of a cylinder that includes a port with the sole port fuel injector. The system further comprises additional instructions to adjust injection of the plurality of direct fuel injectors in response to the reduced performance of the sole port fuel injector. The system further comprises additional instructions to adjust injection timing of the plurality of direct fuel injectors in response to the reduced performance of the sole port fuel injector. The system includes where the plurality of port fuel injectors and the plurality of direct fuel injectors inject a same type of fuel. 
     Referring now to  FIG. 2 , a method for providing air and fuel to an engine that includes two different types of fuel injectors is shown. The method of  FIG. 2  may include and/or cooperate with the methods of  FIGS. 4, 6, 7, 9, 11, and 13 . Further, at least portions of the method of  FIG. 2  may be included as executable instructions in the system of  FIGS. 1A and 1B . Additionally, portions of the method of  FIG. 2  may be actions taken by controller  12  in the physical world to transform vehicle operating conditions. The steps of method  200  are described for a single cylinder receiving fuel during a cylinder cycle. Nevertheless, fuel injections for remaining engine cylinders may be determined in a similar way. 
     At  202 , method  200  determines engine and vehicle operating conditions. Engine and vehicle operating conditions may include but are not limited to vehicle speed, desired torque, accelerator pedal position, engine coolant temperature, engine speed, engine load, engine air flow amount, cylinder air flow amount for each engine cylinder, and ambient temperature and pressure. Method  200  determines operating conditions via querying engine and vehicle sensors. Method  200  proceeds to  204  after operating conditions are determined. 
     At  204 , method  200  determines a desired engine torque. In one example, desired engine torque is based on accelerator pedal position and vehicle speed. The accelerator pedal position and vehicle speed index tables and/or functions that output a desired torque. The tables and/or functions include empirically determined values of desired torque. Accelerator pedal position and vehicle speed provide a basis for indexing the tables and/or functions. In alternative examples, desired engine load may replace desired torque. Method  200  proceeds to  206  after the desired engine torque is determined. 
     At  206 , method  200  determines a desired cylinder fuel amount. In one example, the desired cylinder fuel amount is based on the desired engine torque. In particular, tables and or functions output empirically determined values of desired cylinder fuel amount (e.g., a desired amount of fuel to inject to a cylinder during a cycle of the cylinder (e.g., two engine revolutions)) based on the desired engine torque at the present engine speed. Further, the desired fuel amount may include adjustments for improving catalyst efficiency, reducing exhaust gas temperatures, and vehicle and engine environmental conditions. Method  200  proceeds to  208  after the desired fuel amount is determined. 
     At  208 , method  200  determines desired port fuel injection fraction and desired direct fuel injection fraction. The port fuel injection fraction is a percentage of a total amount of fuel injected to a cylinder during a cylinder cycle that is injected via a port fuel injector. Thus, if the desired fuel amount at  206  is determined to be X grams of fuel and the port injection fraction is 0.6 or 60%, then the port amount of fuel injected is 0.6·X. The port fuel injection fraction plus the direct fuel injection fraction equal a value of one. Thus, the direct fuel injection fraction is 0.4 when the port fuel injection fraction is 0.6. 
     In one example, the port and direct fuel fractions are empirically determined and stored in a table or function that may be indexed via engine speed and desired torque. The tables and/or functions output the port fuel fraction and the direct fuel fraction. 
     The amount of air entering a cylinder may also be determined at  208 . In one example, the amount of air entering a cylinder is an integrated value of air flowing through an air meter during an intake stroke of the cylinder receiving fuel. Further, the air flow through the air meter may be filtered for manifold filling. In still other examples, the amount of air flowing into a cylinder may be determined via intake manifold pressure, engine speed, and the ideal gas law as is known in the art. Method  200  proceeds to  210  after the port and direct fuel injection fractions are determined. 
     At  210 , method  200  determines the desired port fuel injection pulse width and the desired direct fuel injection pulse width. The desired port fuel injection pulse width is determined by multiplying desired fuel amount determined at  206  by the port fuel fraction determined at  208 . A port fuel injector transfer function is then indexed via the resulting fuel amount and the transfer function outputs a fuel injector pulse width. The starting time of the port fuel injector pulse width is at earliest the starting angle of the port fuel injection window. The ending time of the port fuel injector pulse width is a time that provides the desired port fuel injection pulse width after the port fuel injector is opened at the starting time or crankshaft angle of the port fuel injection window, or alternatively, the ending time of the port fuel injector pulse width is the end of the port fuel injection window. The desired port fuel injection pulse width may be revised several times during a cylinder cycle based on updated estimates of air entering the cylinder receiving the fuel only if short port fuel injection windows are enabled. The cylinder air amount may be based on output of a MAP sensor or a mass air flow sensors as is known in the art. Thus, the port fuel injection fuel amount may start out as a larger value and then decrease as the engine rotates through the cylinder cycle. Conversely, the port fuel injection fuel amount may start out as a smaller value and then increase as the engine rotates through the cylinder cycle. 
     The desired direct fuel injection pulse width is determined by multiplying desired fuel amount determined at  206  by the direct fuel fraction determined at  208 . Further, the direct fuel injector pulse width may also revised based on the amount of port injected fuel in the cylinder cycle. In particular, if the port fuel injection window is a short duration window, port fuel injector feedback information is provided to method  600  for determining an amount of fuel to directly inject to the engine as is described in the method of  FIG. 6 . If the port fuel injection window is a long duration, the amount of port fuel injected is based on the scheduled amount of port fuel to inject. Because no port fuel injection updates are allowed when the port fuel injection window is a long duration, the amount of port fuel injected is known at the time the port fuel amount is initially scheduled at intake valve closing as described in the method of  FIG. 4 . Method  200  proceeds to  212  after the desired port and direct fuel injection pulse widths are determined. 
     At  212 , method  200  determines if the port fuel injection window is short or long. If the port fuel injection pulse width determined at  210  is greater than a threshold, the port fuel injection mode is adjusted for a long port fuel injection window. If the port fuel injection pulse is less than or equal to the threshold, the port fuel injection mode is adjusted for a short fuel injection window. Method  200  proceeds to  214  after the port fuel injection window is determined. 
     At  214 , method  200  judges if the port fuel injection window is long. If so, the answer is yes and method  200  proceeds to  218 . Otherwise, the answer is no and method  200  proceeds to  216 . 
     At  216 , method  200  determines the port and direct fuel injection timings according to the method of  FIG. 6 . Method  200  proceeds to  220  after the port and direct fuel injection timing are determined. 
     At  218 , method  200  determines the port and direct fuel injection timings according to the method of  FIG. 4 . Method  200  proceeds to  220  after the port and direct fuel injection timing are determined. 
     At  220 , method  200  determines a desired cylinder air amount. The desired cylinder air amount is determined by multiplying the desired cylinder fuel amount determined at  206  by a desired cylinder air-fuel ratio. Method  200  proceeds to  222  after the desired cylinder air amount is determined. 
     At  222 , method  200  determines modifications to port and direct fuel injection timings as described in the methods of  FIGS. 9, 11, and 13 . Method  200  proceeds to  224  after port and direct fuel injection timings are adjusted. 
     At  224 , method  200  adjusts the cylinder air amounts and fuel injection amounts. In particular, method  200  adjusts engine throttle position and valve timings to provide the desired cylinder air amount as determined at  220 . The throttle may be adjusted based on a throttle model and cam/valve timings may be adjusted based on empirically determined values stored in memory that are indexed via engine speed and the desired cylinder air amount. The port fuel injection pulse width and direct fuel injection pulse widths are output to the port fuel injector and the direct fuel injector of a cylinder in the cylinder&#39;s port and direct fuel injection windows. Method  200  proceeds to exit after the fuel injection pulse widths are output. 
     Referring now to  FIG. 3 , a cylinder timing diagram that includes a long port fuel injection window duration is shown. Timing line  304  begins at the left side of  FIG. 3  and extends to the right side of  FIG. 3 . Time progresses from left to right. Each stroke of cylinder number one is shown as indicated above timing line  304 . The strokes are separated by vertical lines. The sequence begins at a timing of 540 crankshaft degrees before top-dead-center compression stroke. Top-dead-center compression stroke is indicated as 0 crankshaft degrees. Each of the respective cylinder stroke are 180 crankshaft degrees. The piston in cylinder number one is at top-dead-center when the piston is at the locations along timing line  304  where TDC is displayed. The piston in cylinder number one is at bottom-dead-center when the piston is at the locations along timing line  304  where BDC is displayed. Intake valve closing locations are indicated by IVC. Intake valve opening locations are indicated by IVO. Combustion events are indicated by * marks. 
     Locations  350  indicate port injection abort angles. IVC and IVO locations may be different for different engines or when the engine is operated at a different speed and desired torque. Port fuel injection is scheduled at the area at location  306 . The port fuel injection window is indicated by the shaded area at  302 . Port fuel injection pulse widths are indicated by the shaded area at  310 . Direct fuel injection is scheduled at the area at location  308 . The direct fuel injection window is indicated by the shaded area at  304 . Direct fuel injection pulse widths are indicated as the shaded area at  312 . 
     A cylinder cycle may begin at TDC intake stroke and end at TDC intake stroke 720 crankshaft degrees later. Thus, as shown, the duration of a port fuel injection window with a direct fuel injection window extends for more than a single cylinder cycle. For example, port fuel injected in port fuel injection window  360  and direct fuel injected during direct fuel injection window  361  is combusted at  355 . Similarly, port fuel injected in port fuel injection window  363  and direct fuel injected during direct fuel injection window  364  is combusted at  356 . 
     Port fuel injection is first scheduled for a cylinder cycle at IVC (e.g., fuel delivered in window  360  of  FIG. 3 ) of a cylinder cycle preceding a cylinder cycle where the port fuel injected is combusted (e.g., cylinder cycle of combustion event  355  of  FIG. 3 ). Scheduling includes determining port fuel injection pulse width duration and storing the pulse width in a memory location that is accessed to activate and deactivate fuel injection driver circuitry. The port fuel injection window may start at IVC or immediately after port fuel injection scheduling near IVC. The port fuel injection window for a long port fuel injection window ends a predetermined number of crankshaft degrees before IVC for the cylinder cycle where the port injected fuel is combusted and a predetermined number of crankshaft degrees after IVO of the cylinder cycle where the port injected fuel is combusted. Thus, there may be a small number of crankshaft degrees between a port fuel injection window for a first cylinder cycle and a port fuel injection window for a second cylinder cycle. Further, the port fuel injection window may be advanced over several engine cycles as intake valve timing advances over several engine cycles. Additionally, port fuel injection window may be retarded over several engine cycles as intake valve timing is retarded over several engine cycles. No port fuel injection pulse width adjustments are provided during a cylinder cycle once the port fuel injection is scheduled for a long port fuel injection window. The port fuel injection pulse width may be shorter (e.g., as shown) than the port fuel injection window, or it may be as long as the port fuel injection window. If the port fuel injection pulse width is bigger than the port fuel injection window it is truncated to cease port fuel injection for the cylinder cycle at the end of the port fuel injection window. 
     Direct fuel injection is first scheduled for a cylinder cycle at IVO (e.g., fuel delivered during window  361  of  FIG. 3 ) for the cylinder cycle where the direct injected fuel is combusted (e.g., combustion event  355  of  FIG. 3 ). Scheduling includes determining direct fuel injection pulse width duration and storing the pulse width in a memory location that is accessed to activate and deactivate fuel injection driver circuitry. The direct fuel injection window may start at IVO or immediately after direct fuel injection scheduling near IVO. The direct fuel injection window for a cylinder cycle with a long port fuel injection window ends a predetermined number of crankshaft degrees before TDC compression stroke of the cylinder cycle where the direct injected fuel is combusted and a predetermined number of crankshaft degrees after BDC compression stroke of the cylinder cycle where the direct injected fuel is combusted. Thus, there may be a larger number of crankshaft degrees between a direct fuel injection window for a first cylinder cycle and a direct fuel injection window for a second cylinder cycle. Further, the direct fuel injection window starting time or crankshaft angle may be advanced over several engine cycles as intake valve timing advances over several engine cycles. Additionally, direct fuel injection window starting time or crankshaft angle may be retarded over several engine cycles as intake valve timing is retarded over several engine cycles. The direct fuel injection pulse width may be shorter (e.g., as shown) than the direct fuel injection window, or it may be as long as the direct fuel injection window. If the direct fuel injection pulse width is bigger than the direct fuel injection window it is truncated at the end of the direct fuel injection window to cease direct fuel injection for the cylinder cycle. The amount of fuel scheduled for direct injection at  308  is a desired cylinder fuel amount minus the amount of fuel scheduled for port injection at  306 . Thus, the amount of directly injected fuel scheduled at  308  may be determined even though port fuel injection is ongoing at the time of direct injection fuel scheduling. 
     The longer port fuel injection window allows a greater amount of fuel to be inducted and combusted in a cylinder as compared to if only direct injection of fuel is allowed because the amount of directly injected fuel is limited by fuel pump capacity and the duration of intake and compression strokes. Additionally, since the amount of port fuel injected is known well before direct fuel injection is scheduled, the direct fuel injection may be scheduled to accurately supply the desired amount of fuel during a cylinder cycle. 
     Referring now to  FIG. 4 , a method for injecting fuel to an engine with constraints that are based on a long port fuel injection window duration is shown. The method of  FIG. 4  operates in collaboration with the method of  FIGS. 2 and 7 . Further, at least portions of the method of  FIG. 4  may be included as executable instructions in the system of  FIGS. 1A and 1B . Additionally, portions of the method of  FIG. 4  may be actions taken by controller  12  in the physical world to transform vehicle operating conditions. The steps of method  400  are described for a single cylinder receiving fuel during a cylinder cycle. Nevertheless, fuel injections for remaining engine cylinders may be determined in a similar way. Further, the method of  FIG. 4  may provide the operating sequence of  FIG. 3 . 
     At  402 , method  400  judges if the engine is at a crankshaft angle corresponding to a start of a long port fuel injection window for a particular cylinder for a combustion event where fuel that is to be injected during the port fuel injection window is combusted. 
     Engine intake valve and/or exhaust valve timing may constrain port and direct fuel injection timing because engine intake and exhaust valve timing may not strictly adhere to particular cylinder strokes. For example, intake valve opening time may be before or near top-dead-center intake stroke for some engine operating conditions. Conversely, during other engine operating conditions, intake valve opening time may be delayed more than thirty crankshaft degrees after top-dead-center intake stroke during other engine operating conditions. Further, it may not be desirable to directly inject fuel before IVO because the directly injected fuel may be expelled to the engine exhaust without participating in combustion within the engine. As such, it may be desirable to adjust fuel injection timing responsive to intake and exhaust valve opening and closing times or specific crankshaft positions or angles. Port and direct fuel injection windows provide one way of constraining port and direct fuel injection timings so that port and direct fuel injections do not occur at undesirable times and/or engine crankshaft locations so that fuel injected for one cylinder cycle does not enter the cylinder during an unintended different cylinder cycle. The port and direct fuel injection windows may be adjusted responsive to engine intake and exhaust opening and closing times or crankshaft angles. 
     A long port fuel injection window is an engine crankshaft interval where port fuel may be injected to a cylinder port during a cylinder cycle with no revisions to the port fuel injection pulse width possible while the long port fuel injection window is open (e.g., a time port fuel injection via the port fuel injector pulse width is permitted). The port fuel injection pulse width time or duration may be shorter or equal to the long port fuel injection window. If the port fuel injection pulse width exceeds the long port fuel injection window, the port fuel injection pulse width will be truncated so that port fuel injection ceases when the port fuel injector pulse width is not within the long port fuel injection window. The engine crankshaft location where the long port fuel injection window ends may be referred to as a port injection abort angle because the port fuel injection pulse is aborted at times or crankshaft angles after the port injection abort angle during a cylinder cycle. The long port fuel injection ending time or crankshaft angle is at or after an intake valve opening crankshaft angle of the cylinder receiving fuel during the cylinder cycle and before an intake valve closing crankshaft angle for the present cylinder cycle. The starting crankshaft angle of the port fuel injection pulse width is required to be at or after the start of the long port fuel injection window during a cylinder cycle. The starting crankshaft angle for the long port fuel injection window is at or later than (e.g., retarded from) an intake valve closing for a cylinder cycle previous to the cylinder cycle where the port injected fuel is combusted. The long port fuel injection window starting crankshaft angle and ending crankshaft angle may be empirically determined and stored in a table and/or function in memory that is indexed via engine speed and desired torque. Thus, the starting crankshaft angle and the ending crankshaft angle of the long port fuel injection window may change at a same amount or equally with intake valve timing of the cylinder receiving the port injected fuel. 
     In one example, the start of the long port fuel injection window crankshaft angle is IVC for a cylinder cycle before a cylinder cycle where the port injected fuel is combusted as is shown in  FIG. 3 . If method  400  judges that the engine is at the crankshaft angle corresponding to the start of the long port fuel injection window, the answer is yes and method  400  proceeds to  404 . Otherwise, the answer is no and method  400  proceeds to  430 . 
     At  430 , method  400  performs previously determined fuel injections (e.g., port and direct fuel injections) or waits if previously determined fuel injections are complete. The previously determined fuel injections may be for the present cylinder or a different engine cylinder. Method  400  returns to  402  after performing previously scheduled fuel injections. 
     At  404 , method  400  determines a desired fuel injection mass for a port fuel injector. Method  400  may retrieve the desired fuel injection mass for the port fuel injector from step  208  of  FIG. 2  or calculate the port fuel mass as described in  FIG. 2 . Method  400  proceeds to  406  after determining the port fuel injection fuel mass. 
     At  406 , method  400  determines a fuel injector pulse width for the port fuel injector. Method  400  may retrieve the port fuel injector pulse width from step  210  of  FIG. 2  or calculate the port fuel injector pulse width as described in  FIG. 2 . Method  400  proceeds to  408  after the port fuel injector pulse width is determined. 
     At  408 , method  400  determines port fuel injection pulse width modifications according to the method of  FIG. 9 . Method  400  proceeds to  410  after the port fuel injection pulse widths are modified. 
     At  410 , method  400  schedules the port fuel injection pulse width. The port fuel injection is scheduled by writing the pulse width to a memory location that is a basis for activating the port fuel injector. The port fuel injection pulse width starting engine crankshaft angle for the cylinder cycle is the starting engine crankshaft angle of the long port fuel injector window, or it may be delayed a predetermined number of engine crankshaft degrees. The port fuel injector is activated and opened to allow fuel flow at the starting of the long port fuel injector window for the duration of the port fuel injector pulse width or the abort angle, whichever is earlier in time. Method  400  proceeds to  412  after the port fuel injection is scheduled and delivery begins. 
     At  412 , method  400  equates the actual port fuel injection (PFI) fuel mass equal to a desired port fuel injection mass since port fuel injection updates are not provided and since the desired port fuel injection mass does not change after the port fuel injection pulse width is scheduled. Method  400  proceeds to  414  after determining the actual port fuel injection fuel mass. 
     At  414 , method  400  judges if the engine is at a start of the direct fuel injection window. A direct fuel injection window is an engine crankshaft interval where fuel may be directly injected to a cylinder during a cylinder cycle. The direct fuel injection pulse width time or duration may be shorter or equal to the direct fuel injection window. If the direct fuel injection pulse width exceeds the direct fuel injection window, the direct fuel injection pulse width will be truncated so that direct fuel injection ceases at the end of the direct fuel injection window. The engine crankshaft location where the direct fuel injection window ends may be referred to as a direct injection abort angle because the direct fuel injection pulse is aborted at times or crankshaft angles after the direct injection abort angle during a cylinder cycle. The starting crankshaft angle of the direct fuel injection pulse width is required to be at or after (e.g., retarded from) the start of the direct fuel injection window during a cylinder cycle. The direct fuel injection window begins at or a predetermine number of crankshaft degrees after intake valve opening for the cylinder receiving the fuel. The direct fuel injection window ends at, or a predetermined number of engine crankshaft degrees, before top-dead-center compression stroke of the cylinder receiving the fuel and after the intake valve closing in the cylinder cycle when the directly injected fuel is combusted. The direct fuel injection window starting crankshaft angle and ending crankshaft angle may be empirically determined and stored in a table and/or function in memory that is indexed via engine speed and desired torque. Thus, the starting crankshaft angle and the ending crankshaft angle of the direct fuel injection window may change at a same amount or equally with intake valve timing of the cylinder receiving the port injected fuel. 
     In one example, the start of the direct fuel injection window crankshaft angle is IVO for a cylinder cycle where the direct injected fuel is combusted as is shown in  FIG. 3 . If method  400  judges that the engine is at the crankshaft angle corresponding to the start of the direct fuel injection window, the answer is yes and method  400  proceeds to  416 . Otherwise, the answer is no and method  400  returns to  414 . 
     At  416 , method  400  determines a desired fuel injection mass for a direct fuel injector. Method  400  may retrieve the desired fuel injection mass for the direct fuel injector from step  208  of  FIG. 2  or calculate the direct fuel mass as described in  FIG. 2 . Method  400  proceeds to  418  after determining the direct fuel injection fuel mass. 
     At  418 , method  400  determines a fuel injector pulse width for the direct fuel injector. Method  400  may retrieve the direct fuel injector pulse width from step  210  of  FIG. 2  or calculate the port fuel injector pulse width as described in  FIG. 2 . In particular, the direct fuel injection pulse width is adjusted to provide the desired mass of fuel determined at  206  minus the mass of port injected fuel determined at  412 . The direct fuel injector pulse width is then determined via indexing a table or function that is indexed by a desired direct injection fuel mass and outputs a direct injector fuel pulse width. Method  400  proceeds to  420  after the direct fuel injector pulse width is determined. 
     At  420 , method  400  schedules the direct fuel injection pulse width. The direct fuel injection is scheduled by writing the pulse width to a memory location that is a basis for activating the direct fuel injector. The direct fuel injection pulse width starting engine crankshaft angle for the cylinder cycle is the starting engine crankshaft angle of the direct fuel injector window, or it may be delayed a predetermined number of engine crankshaft degrees. The direct fuel injector is activated and opened to allow fuel flow at the starting of the direct fuel injector window for the duration of the direct fuel injector pulse width or the abort angle, whichever is earlier in time. Additionally, in some examples, the direct injection pulse width may be revised in the cylinder cycle in which it is injected based on air flow into the cylinder receiving the fuel while the intake valve of the cylinder is open. Method  400  proceeds to return to  402  after the direct fuel injection is scheduled and delivery begins. 
     Thus, the port and direct fuel injection windows are crankshaft intervals where respective port and direct fuel injection are permitted, and they bound fuel injection pulse widths to engine crankshaft angles where the injected fuel may participated in combustion for a particular cylinder cycle. The port and direct fuel injection windows prevent injected fuel from participating in combustion events of cylinder cycles that are not intended to receive the injected fuel. The port and direct fuel injection windows also operate to cease port and direct fuel injection if the port and/or direct fuel injection pulses are outside of the respective port and direct fuel injection windows. 
     Referring now to  FIG. 5 , a cylinder timing diagram that includes a short port fuel injection window duration is shown. Timing line  504  begins at the left side of  FIG. 5  and extends to the right side of  FIG. 5 . Time progresses from left to right. Each stroke of cylinder number one is shown as indicated above timing line  504 . The strokes are separated by vertical lines. The sequence begins at a timing of 540 crankshaft degrees before top-dead-center compression stroke. Top-dead-center compression stroke is indicated as 0 crankshaft degrees. Each of the respective cylinder stroke are 180 crankshaft degrees. The piston in cylinder number one is at top-dead-center when the piston is at the locations along timing line  504  where TDC is displayed. The piston in cylinder number one is at bottom-dead-center when the piston is at the locations along timing line  304  where BDC is displayed. Intake valve closing locations are indicated by IVC. Intake valve opening locations are indicated by IVO. Combustion events are indicated by * marks. 
     Locations  550  indicate port injection abort angles. IVC and IVO locations may be different for different engines or when the engine is operated at a different speed and desired torque. Port fuel injection is scheduled at the area at location  506 . The port fuel injection window is indicated by the shaded area at  502 . Port fuel injection pulse widths are indicated by the shaded area at  510 . Direct fuel injection is scheduled at the area at location  508 . The direct fuel injection window is indicated by the shaded area at  504 . Direct fuel injection pulse widths are indicated as the shaded area at  512 . 
     A cylinder cycle may begin at TDC intake stroke and end at TDC intake stroke 720 crankshaft degrees later. Thus, as shown, the duration of a port fuel injection window with a direct fuel injection window extends for more than a single cylinder cycle. For example, port fuel injected in port fuel injection window  560  and direct fuel injected during direct fuel injection window  561  is combusted at  555 . Similarly, port fuel injected in port fuel injection window  563  and direct fuel injected during direct fuel injection window  564  is combusted at  556 . 
     Port fuel injection is first scheduled for a cylinder cycle at IVC (e.g., fuel delivered in window  560  of  FIG. 5 ) of a cylinder cycle preceding a cylinder cycle where the port fuel injected is combusted (e.g., cylinder cycle of combustion event  555  of  FIG. 5 ). Scheduling includes determining port fuel injection pulse width duration and storing the pulse width in a memory location that is accessed to activate and deactivate fuel injection driver circuitry. The port fuel injection window may start at IVC or immediately after port fuel injection scheduling near IVC. The port fuel injection window for a short port fuel injection window ends a predetermined number of crankshaft degrees before IVO for the cylinder cycle where the port injected fuel is combusted. Thus, there may be a larger number of crankshaft degrees between a port fuel injection window for a first cylinder cycle and a port fuel injection window for a second cylinder cycle for a short duration port fuel injection window as compared to a long port fuel injection window. 
     Further, the port fuel injection window may be advanced over several engine cycles as intake valve timing advances over several engine cycles. Additionally, port fuel injection window may be retarded over several engine cycles as intake valve timing is retarded over several engine cycles. A plurality of port fuel injection pulse width adjustments may be provided during a cylinder cycle once the port fuel injection is scheduled for a short port fuel injection window. The port fuel injection pulse width may be shorter (e.g., as shown) than the port fuel injection window, or it may be as long as the port fuel injection window. If the port fuel injection pulse width is bigger than the port fuel injection window it is truncated to cease port fuel injection for the cylinder cycle at the end of the port fuel injection window. 
     Direct fuel injection is first scheduled for a cylinder cycle at IVO (e.g., fuel delivered during window  561  of  FIG. 5 ) of the cylinder cycle where the direct injected fuel is combusted (e.g., combustion event  555  of  FIG. 5 ). Scheduling includes determining direct fuel injection pulse width duration and storing the pulse width in a memory location that is accessed to activate and deactivate fuel injection driver circuitry. The direct fuel injection window may start at IVO or immediately after direct fuel injection scheduling near IVO. The direct fuel injection window for a cylinder cycle with a short port fuel injection window ends a predetermined number of crankshaft degrees before TDC compression stroke of the cylinder cycle where the direct injected fuel is combusted and a predetermined number of crankshaft degrees after BDC compression stroke of the cylinder cycle where the direct injected fuel is combusted. Thus, there may be a larger number of crankshaft degrees between a direct fuel injection window for a first cylinder cycle and a direct fuel injection window for a second cylinder cycle. 
     Further, the direct fuel injection window starting time or crankshaft angle may be advanced over several engine cycles as intake valve timing advances over several engine cycles. Additionally, direct fuel injection window starting time or crankshaft angle may be retarded over several engine cycles as intake valve timing is retarded over several engine cycles. The direct fuel injection pulse width may be shorter (e.g., as shown) than the direct fuel injection window, or it may be as long as the direct fuel injection window. If the direct fuel injection pulse width is bigger than the direct fuel injection window it is truncated to cease port fuel injection for the cylinder cycle at the end of the direct fuel injection window. The amount of fuel scheduled for direct injection at  508  is a desired cylinder fuel amount minus the amount of fuel port injected for the duration of the short port fuel injection window including port fuel injection pulse width adjustments made as the engine rotates. The total amount of port injected fuel is output at abort angle  550  or sooner in the cylinder cycle and it is the basis for scheduling direct fuel injection at  508 . Thus, the amount of directly injected fuel scheduled at  508  may be determined based on multiple updates to the port fuel injection pulse width during the cylinder cycle. 
     The shorter port fuel injection window allows port fuel injection to cease before direct fuel injection is scheduled for the cylinder cycle. This allows the direct fuel injection amount to be adjusted based on the adjusted amount of port fuel injected to the engine during the cylinder cycle in which the fuel is directly injected. Leaders  510  indicate that feedback (e.g., latest port fuel injection pulse width duration and fuel pressure) may be a basis for adjusting the amount of fuel directly injected so that the desired amount of fuel enters the cylinder even though the port fuel injection pulse width was updated a plurality of times. 
     Referring now to  FIG. 6 , a method for injecting fuel to an engine with constraints that are based on a short port fuel injection window duration is shown. The method of  FIG. 6  operates in collaboration with the method of  FIGS. 2 and 7 . Further, at least portions of the method of  FIG. 6  may be included as executable instructions in the system of  FIGS. 1A and 1B . Additionally, portions of the method of  FIG. 6  may be actions taken by controller  12  in the physical world to transform vehicle operating conditions. The steps of method  600  are described for a single cylinder receiving fuel during a cylinder cycle. Nevertheless, fuel injections for remaining engine cylinders may be determined in a similar way. Further, the method of  FIG. 6  may provide the operating sequence of  FIG. 5 . 
     At  602 , method  600  judges if the engine is at a crankshaft angle corresponding to a start of a short port fuel injection window for a particular cylinder for a combustion event where fuel that is to be injected during the port fuel injection window is combusted. 
     A short port fuel injection window is an engine crankshaft interval where port fuel may be injected to a cylinder port during a cylinder cycle with multiple revisions to the port fuel injection pulse width possible while the short port fuel injection window is open (e.g., a time port fuel injection is permitted). The port fuel injection pulse width time or duration may be shorter or equal to the short port fuel injection window. If the port fuel injection pulse width exceeds the short port fuel injection window, the port fuel injection pulse width will be truncated or ceased at the end of the short port fuel injection window. 
     The engine crankshaft location where the short port fuel injection window ends may be referred to as a port injection abort angle because the port fuel injection pulse is aborted at times or crankshaft angles after the port injection abort angle during a cylinder cycle. The short port fuel injection ending time or crankshaft angle is at or before intake valve opening crankshaft angle of the cylinder receiving fuel during the cylinder cycle. The starting crankshaft angle of the port fuel injection pulse width is required to be at or after the start of the short port fuel injection window during a cylinder cycle. The starting crankshaft angle for the short port fuel injection window is at or later than (e.g., retarded from) an intake valve closing for a cylinder cycle previous to the cylinder cycle where the port injected fuel is combusted. The short port fuel injection window starting crankshaft angle and ending crankshaft angle may be empirically determined and stored in a table and/or function in memory that is indexed via engine speed and desired torque. 
     In one example, the start of the short port fuel injection window crankshaft angle is IVC for a cylinder cycle before a cylinder cycle where the port injected fuel is combusted as is shown in  FIG. 5 . If method  600  judges that the engine is at the crankshaft angle corresponding to the start of the short port fuel injection window, the answer is yes and method  600  proceeds to  604 . Otherwise, the answer is no and method  600  proceeds to  630 . 
     At  630 , method  600  performs previously determined fuel injections (e.g., port and direct fuel injections) or waits if previously determined fuel injections are complete. The previously determined fuel injections may be for the present cylinder or a different engine cylinder. Method  600  returns to  602  after performing previously scheduled fuel injections. 
     At  604 , method  600  determines a desired fuel injection mass for a port fuel injector. Method  600  may retrieve the desired fuel injection mass for the port fuel injector from step  208  of  FIG. 2  or calculate the port fuel mass as described in  FIG. 2 . Method  600  proceeds to  606  after determining the port fuel injection fuel mass. 
     At  606 , method  600  determines a fuel injector pulse width for the port fuel injector. Method  600  may retrieve the port fuel injector pulse width from step  210  of  FIG. 2  or calculate the port fuel injector pulse width as described in  FIG. 2 . Method  600  proceeds to  608  after the port fuel injector pulse width is determined. 
     At  608 , method  600  determines port fuel injection pulse width modifications according to the method of  FIG. 9 . Method  600  proceeds to  610  after the port fuel injection pulse widths are modified. 
     At  610 , method  600  schedules the port fuel injection pulse width. The port fuel injection is scheduled by writing the pulse width to a memory location that is a basis for activating the port fuel injector. The port fuel injection pulse width starting engine crankshaft angle for the cylinder cycle is the starting engine crankshaft angle of the short port fuel injector window, or it may be delayed a predetermined number of engine crankshaft degrees. The port fuel injector is activated and opened to allow fuel flow at the starting of the short port fuel injector window for the duration of the port fuel injector pulse width or the abort angle, whichever is earlier in time. Method  600  proceeds to  612  after the port fuel injection is scheduled and delivery begins. 
     At  612 , method  600  judges if the engine is at the port fuel injection (PFI) abort angle for the present engine cylinder receiving fuel. In one example as shown in  FIG. 5 , the abort angle is a predetermined number of crankshaft degrees before intake valve opening during the cycle the cylinder receives the fuel. If method  600  judges that the engine is at the port fuel injection abort angle, the answer is yes and method  600  proceeds to  614 . Otherwise, method  600  returns to  604  where the port fuel injection pulse width may be revised. 
     At  614 , method  600  determines the total time the port fuel injector was on during the short fuel injection window by adding together the total time the port fuel injector was activated or open during the port fuel injection window. The total time is used to index a transfer function describing port fuel injector flow and the transfer function outputs a mass of fuel injected during port fuel injection. Method  600  proceeds to  616  after determining the actual port fuel injection fuel mass. 
     At  616 , method  600  judges if the engine is at a start of the direct fuel injection window. A direct fuel injection window is an engine crankshaft interval where fuel may be directly injected to a cylinder during a cylinder cycle. The direct fuel injection pulse width time or duration may be shorter or equal to the direct fuel injection window. If the direct fuel injection pulse width exceeds the direct fuel injection window, the direct fuel injection pulse width will be truncated so that direct fuel injection for the cylinder cycle ceases at the end of the direct fuel injection window. The engine crankshaft location where the direct fuel injection window ends may be referred to as a direct injection abort angle because the direct fuel injection pulse is aborted at times or crankshaft angles after the direct injection abort angle during a cylinder cycle. The starting crankshaft angle of the direct fuel injection pulse width is required to be at or after (e.g., retarded from) the start of the direct fuel injection window during a cylinder cycle. The direct fuel injection window begins at or a predetermine number of crankshaft degrees after intake valve opening for the cylinder receiving the fuel. The direct fuel injection window ends at, or a predetermined number of engine crankshaft degrees, before top-dead-center compression stroke of the cylinder receiving the fuel and after the intake valve closing in the cylinder cycle when the directly injected fuel is combusted. The direct fuel injection window starting crankshaft angle and ending crankshaft angle may be empirically determined and stored in a table and/or function in memory that is indexed via engine speed and desired torque. Thus, the starting crankshaft angle and the ending crankshaft angle of the direct fuel injection window may change at a same amount or equally with intake valve timing of the cylinder receiving the port injected fuel. 
     In one example, the start of the direct fuel injection window crankshaft angle is IVO for a cylinder cycle where the direct injected fuel is combusted as is shown in  FIG. 5 . If method  600  judges that the engine is at the crankshaft angle corresponding to the start of the direct fuel injection window, the answer is yes and method  600  proceeds to  618 . Otherwise, the answer is no and method  600  returns to  616 . 
     At  618 , method  600  determines a desired fuel injection mass for a direct fuel injector. Method  600  may retrieve the desired fuel injection mass for the direct fuel injector from step  208  of  FIG. 2  or calculate the direct fuel mass as described in  FIG. 2 . Method  600  proceeds to  620  after determining the direct fuel injection fuel mass. 
     At  620 , method  600  determines a fuel injector pulse width for the direct fuel injector. Method  600  may retrieve the direct fuel injector pulse width from step  210  of  FIG. 2  or calculate the port fuel injector pulse width as described in  FIG. 2 . In particular, the direct fuel injection pulse width is adjusted to provide the desired mass of fuel determined at  206  minus the mass of port injected fuel determined at  612 . The direct fuel injector pulse width is then determined via indexing a table or function that is indexed by a desired direct fuel injection fuel mass and outputs a direct fuel injection fuel pulse width. Additionally, in some examples, the direct injection pulse width may be revised in the cylinder cycle in which it is injected based on air flow into the cylinder receiving the fuel while the intake valve of the cylinder is open. Method  600  proceeds to  622  after the direct fuel injector pulse width is determined. 
     At  622 , method  600  schedules the direct fuel injection pulse width. The direct fuel injection is scheduled by writing the pulse width to a memory location that is a basis for activating the direct fuel injector. The direct fuel injection pulse width starting engine crankshaft angle for the cylinder cycle is the starting engine crankshaft angle of the direct fuel injector window, or it may be delayed a predetermined number of engine crankshaft degrees. The direct fuel injector is activated and opened to allow fuel flow at the starting of the direct fuel injector window for the duration of the direct fuel injector pulse width or the abort angle, whichever is earlier in time. Method  600  proceeds to return to  602  after the direct fuel injection is scheduled and delivery begins. 
     Referring now to  FIG. 7 , a method for providing short and long port fuel injection windows and transitioning between the windows is shown. The method of  FIG. 7  may provide the operating sequence shown in  FIG. 8 . Further, at least portions of the method of  FIG. 7  may be included as executable instructions in the system of  FIGS. 1A and 1B . Additionally, portions of the method of  FIG. 7  may be actions taken by controller  12  in the physical world to transform vehicle operating conditions. The steps of method  700  are described for a single cylinder receiving fuel during a cylinder cycle. Nevertheless, fuel injections for remaining engine cylinders may be determined in a similar way. 
     At  702 , method  700  begins with providing short port fuel injection windows and direct fuel injection windows. An example short port fuel injection window is shown in  FIG. 5 . A port fuel injection abort angle is provided before an engine crankshaft angle where direct fuel injection is scheduled (e.g., IVO during the cylinder cycle where the direct fuel is injected). Additionally, the port fuel injection pulse width or pulse widths may be updated a plurality of times during the cycle the cylinder receives the port injected fuel. Feedback of an amount of port fuel injector on time during the port fuel injection window for the cylinder cycle is also provided for scheduling direct fuel injection after the port fuel injection during a same cylinder cycle. There is no limit on a number of port fuel injection pulses for the cylinder in the port fuel injection window for the cylinder cycle. Method  700  proceeds to  704  after short port fuel injection windows and direct fuel injection windows are established at  702 . 
     At  704 , method  700  judges if a port fuel injection pulse width for a cylinder cycle is greater than a threshold. If not, the answer is no and method  700  returns to  702 . Otherwise, the answer is yes and method  700  proceeds to  706 . 
     At  706 , method  700  begins to transition to providing long port fuel injection windows and direct fuel injection windows. During the transition to long port fuel injection windows, the port fuel injection window is short and a port fuel injection abort angle is provided after an engine crankshaft angle where direct fuel injection is scheduled (e.g., IVO for the cylinder cycle where the direct fuel is injected). Additionally, the port fuel injection pulse width or pulse widths may not be updated a plurality of times during the cycle the cylinder receives the port injected fuel. Feedback of an amount of port fuel injector on time during the port fuel injection window for the cylinder cycle is not provided for scheduling direct fuel injection. Instead, the direct fuel injection pulse width is based on the port fuel injection pulse width schedules at the beginning of the port fuel injection window and the desired cylinder fuel amount. Only one port fuel injection pulse width for the cylinder is provided in the port fuel injection window during the cylinder cycle. Method  700  proceeds to  708  after short port fuel injection windows and direct fuel injection windows are established at  706 . 
     At  708 , method  700  judges if all port fuel injection abort angles for all engine cylinders have been moved to a more retarded timing. If not, the answer is no and method  700  returns to  706 . Otherwise, the answer is yes and method  700  proceeds to  710 . 
     At  710 , method  700  begins with providing long port fuel injection windows and direct fuel injection windows. An example long port fuel injection window is shown in  FIG. 3 . A port fuel injection abort angle is provided after an engine crankshaft angle where direct fuel injection is scheduled (e.g., IVO during the cylinder cycle where the direct fuel is injected) and before IVC for the cylinder receiving the fuel. Additionally, the port fuel injection pulse width or pulse widths may not be updated during the cycle the cylinder receives the port injected fuel. Feedback of an amount of port fuel injector on time during the port fuel injection window for the cylinder cycle is not provided for scheduling direct fuel injection during a same cylinder cycle. There is a limit of only one port fuel injection pulse for the cylinder in the port fuel injection window for the cylinder cycle. Method  700  proceeds to  712  after long port fuel injection windows and direct fuel injection windows are established at  710 . 
     At  712 , method  700  judges if a port fuel injection pulse width for a cylinder cycle is less than or equal the threshold. If not, the answer is no and method  700  returns to  710 . Otherwise, the answer is yes and method  700  proceeds to  714 . 
     At  714 , method  700  begins to transition to providing short port fuel injection windows and direct fuel injection windows. During the transition to short port fuel injection windows, the port fuel injection window is short and a port fuel injection abort angle is move to before an engine crankshaft angle where direct fuel injection is scheduled (e.g., IVO for the cylinder cycle where the direct fuel is injected). Further, the port fuel injection pulse width or pulse widths may not be updated a plurality of times during the cycle the cylinder receives the port injected fuel. Feedback of an amount of port fuel injector on time during the port fuel injection window for the cylinder cycle is not provided for scheduling direct fuel injection. Instead, the direct fuel injection pulse width is based on the port fuel injection pulse width schedules at the beginning of the port fuel injection window and the desired cylinder fuel amount. Only one port fuel injection pulse width for the cylinder is provided in the port fuel injection window during the cylinder cycle. Method  700  proceeds to  716  after short port fuel injection windows and direct fuel injection windows are established at  714 . 
     At  716 , method  700  judges if all port fuel injection abort angles for all engine cylinders have been moved to a more advanced timing. If not, the answer is no and method  700  returns to  714 . Otherwise, the answer is yes and method  700  returns to  702 . 
     In this way, method  700  adjusts abort angles and port fuel injections so that port fuel injection windows transition between longer and shorter durations. A transition between modes is complete when all abort angles have been moved to new crankshaft angles. 
     Referring now to  FIG. 8 , an example sequence of transitioning between short and long port fuel injection windows according to the method of  FIG. 7  is shown. Vertical markers at T 1 -T 3  represent times of interest during the sequence. The plots are time aligned. The sequence of  FIG. 8  may be provided by the system of  FIG. 7  executing instructions based on the method of  FIG. 7 . 
     The first plot from the top of  FIG. 8  is a plot of desired torque versus time. The vertical axis represents desired torque and desired torque increases in the direction of the vertical axis arrow. The horizontal axis represents time and time increases from the right side of the plot to the left side of the plot. 
     The second plot from the top of  FIG. 8  is a plot of engine speed versus time. The vertical axis represents engine speed and engine speed increases in the direction of the vertical axis arrow. The horizontal axis represents time and time increases from the right side of the plot to the left side of the plot. 
     The third plot from the top of  FIG. 8  is a plot of port fuel injector pulse width versus time. The vertical axis represents port fuel injector pulse width and port fuel injection pulse width increases in the direction of the vertical axis arrow. The horizontal axis represents time and time increases from the right side of the plot to the left side of the plot. Horizontal line  802  represents a threshold pulse width above which long port fuel injector windows are provided and below which short port fuel injector windows are provided. 
     The fourth plot from the top of  FIG. 8  is a plot of port fuel injector (PFI) fuel injection window state versus time. The vertical axis represents PFI fuel injection window state. The PFI window is long when the trace is at a higher level near the vertical axis arrow. The PFI window is short when the trace is at a lower level near the horizontal axis. The horizontal axis represents time and time increases from the right side of the plot to the left side of the plot. 
     At time T 0 , the desired torque is low, engine speed is low, the port fuel injection pulse width is less than threshold  802 , and the PFI window duration is short. Such conditions may be present during engine idle conditions. 
     At time T 1 , the desired torque begins to increase and the port fuel injection pulse width begins to increase with the desired torque. The desired torque increases in response to a driver applying an accelerator pedal. The engine speed also begins to increase and the PFI window duration remains short. 
     At time T 2 , the desired torque has increased to a level where the port fuel injection pulse width is greater than threshold  802 . The PFI window transitions to a long window in response to the port fuel injection pulse width exceeding threshold  802 . The engine speed continues to increase as the desired torque continues to increase. 
     Between time T 2  and time T 3 , the desired torque levels off to a constant value and then begins to decrease. The engine speed changes due to transmission gear shifting and then decreases as the desired torque decreases. The port fuel injection pulse width increases with desired torque and then decreases as desired torque decreases. The PFI injection window remains long. 
     At time T 3 , the port fuel injection pulse width decreases to a value less than threshold  802 . Consequently, the PFI injection window transitions from long to short. The desired torque continues to decrease as does the engine speed. 
     In this way, port fuel injection windows may transition between short and long durations. The longer duration windows provide for increasing the amount of port injected fuel while the short duration windows provide for updating the amount of port injected fuel for changing engine operating conditions. 
     Referring now to  FIG. 9 , an example method for adjusting fractions of port injected fuel and direct injected fuel to reduce particulate matter produced by an engine is shown. The method of  FIG. 9  may provide the operating sequence shown in  FIG. 10 . Additionally, at least portions of the method of  FIG. 9  may be included as executable instructions in the system of  FIG. 1 . Further, portions of the method of  FIG. 9  may be actions taken by controller  12  in the physical world to transform vehicle operating conditions. 
     At  902 , method  900  judges whether or not the vehicle in which an engine operates is being operated with an alternative calibration. The alternative calibration may be comprised of engine control parameters (e.g., a group of pre-customer delivery control parameters) with which the engine is operated before the vehicle and engine are delivered to a customer. The alternative calibration may be active during vehicle manufacture and transportation to the retail sales location. A nominal calibration (e.g., a group of post-customer delivery control parameters) may be activated at the retail sales location for delivery to the customer. The alternative calibration may be active for a predetermined number of engine starts or until the vehicle has driven a predetermined distance (e.g., 1 Km). If method  900  judges that the engine is operating with an alternative calibration, the answer is yes and method  900  proceeds to  904 . Otherwise, the answer is no and method  900  proceeds to  906 . 
     At  904 , method  900  increases a fraction of port injected fuel for at least some engine operating conditions as compared to if the engine were operated with the nominal calibration provided to the customer. The port injected fuel fraction may be increased by a constant value, or alternatively, a table or function may increase the port injected fuel fraction based on engine speed and desired torque. By increasing the port injected fuel fraction, the engine may produce less carbonaceous soot so that particulate filter loading may be reduced before delivery of the vehicle to a customer. For example, a base engine calibration may provide a port fuel injection fraction of 20% and a direct fuel injection fraction of 80% for an engine speed of 1000 RPM and desired torque of 50 N-m. Method  900  may increase the port fuel injection fraction to 30% and decrease the direct fuel injection fraction to 70% of the total amount of fuel injected at the same 1000 RPM and 50 N-m operating conditions. However, the cylinder&#39;s air-fuel ratio for a same engine speed and load before and after the port fuel injection fraction is adjusted is the same. Further, since the vehicle may be operated inside of an enclosed building during manufacture, it may be desirable to reduce soot production by the engine. Method  900  proceeds to exit after a fraction of port fuel injected to an engine is increased as compared to a fraction of port injected fuel provided by a nominal calibration. 
     At  906 , method  900  judges whether or not a loading of a particulate filter in a vehicle exhaust system is greater than a threshold amount. In other words, method  900  judges if an amount of soot collected in a particulate filter is greater than a threshold. The amount of soot accumulation in the particulate filter may be estimated based of a pressure drop across the particulate filter or from a model of engine soot output and particulate filter storage efficiency. If method  900  judges that the more than a threshold amount of soot is accumulated in the particulate filter, the answer is yes and method  900  proceeds to  908 . Otherwise, the answer is no and method  900  proceeds to  910 . 
     At  908 , method  900  increases a fraction of port injected fuel for at least some engine operating conditions as compared to if the engine were operated with less than the threshold amount of soot accumulated in the particulate filter. The port injected fuel fraction may be increased by a constant value, or alternatively, a table or function may increase the port injected fuel fraction proportionately with an amount of soot accumulated in the particulate filter. For example, if soot accumulated in the particulate filter is greater than a threshold value and increases further by 10%, the fraction of port injected fuel may increase from a fraction of 10% to a fraction of 20% and the fraction of direct injected fuel may decrease from a fraction of 90% to a fraction of 80%. By increasing the port injected fuel fraction, the engine may produce less carbonaceous soot so that particulate filter loading may be reduced before the particulate filter may be purged of soot. Additionally, a port fuel injection abort angle may be advanced in response to an increase in particulate matter stored in the particulate filter and vice-versa. Likewise, a port fuel injection window duration may be adjusted responsive to an amount of soot stored in the particulate filter (e.g., decreased as the amount of stored particulate matter increases and vice-versa). Method  900  proceeds to exit after a fraction of port fuel injected to an engine is increased as compared to a fraction of port injected fuel injected when soot accumulated in the particulate filter is less than the threshold. 
     At  910 , method  900  judges whether or not the vehicle in which the engine operates is in a low particulate environment (e.g., an environment beyond the vehicle such as a garage). A low particulate environment may include but is not limited to an enclosed building, a parking garage, an urban area with a population density greater than a threshold amount, or a road where vehicle speed and/or acceleration are limited to less than predetermined thresholds. Method  900  may judge that the vehicle is in a parking garage or enclosed building via vehicle sensors such as a global positioning system (GPS) receiver, vehicle camera, vehicle lasers, vehicle sonic devices, or radar. Method  900  may judge that the vehicle is in an urban area or an operating on a road where vehicle speed/acceleration are limited to less than predetermined thresholds via the GPS receiver. Further, method  900  may judge that the vehicle is operating in a low particulate environment if vehicle speed is less than a threshold value for more than a threshold amount of time. If method  900  judges that the vehicle and engine are operating in a low particulate environment, the answer is yes and method  900  proceeds to  912 . Otherwise, the answer is no and method  900  proceeds to  914 . 
     At  912 , method  900  increases a fraction of port injected fuel for at least some engine operating conditions as compared to if the engine were not operating within a low particulate environment. The port injected fuel fraction may be increased by a constant value, or alternatively, a table or function may increase the port injected fuel fraction based on engine speed and desired torque. For example, the engine is operating in a low particulate environment, such as an urban area, the fraction of port injected fuel may increase from a value of 60% to a value of 75% and the directly injected fuel fraction may decrease from a value of 40% to a value of 25% so that a same engine air-fuel ratio is provided for a same engine speed and load before and after adjusting the port fuel injection fraction. By increasing the port injected fuel fraction, the engine may produce less carbonaceous soot so that the possibility of releasing soot to the atmosphere may be reduced. Method  900  proceeds to exit after a fraction of port fuel injected to an engine is increased as compared to a fraction of port injected fuel injected when the engine is not operated in a low particulate environment. Of course, additional conditions or geographical locations may be deemed low particulate environments. 
     At  914 , method  900  operates the engine with nominal port fuel injection and direct fuel injection fractions (e.g., port and direct fuel injection fractions not adjusted for operating environment or particulate filter loading, such as a base engine and vehicle calibration). If the engine were previously operating in a low particulate environment, the port fuel injection fraction may be reduced to provide a nominal port fuel injection fraction of a base vehicle calibration. Method  900  proceeds to exit after the engine&#39;s port and direct fuel injection fractions are adjusted. 
     In this way, an amount of particulate matter produced by an engine may be adjusted for environmental conditions and particulate filter loading. By reducing particulate matter formation, it may be possible to delay particulate filter purging until the vehicle reaches conditions that may be more suitable for particulate filter purging. Further, for each of the steps of method  900  where the port fuel injection fraction is increased, the direct fuel injection fraction is decreased so that a same amount of fuel is injected to the cylinder for a same group of engine operating conditions. Consequently, the engine air-fuel ratio is not affected by increasing the port fuel injection fraction. 
     Referring now to  FIG. 10 , an example operating sequence according to the method of  FIG. 9  is shown. The operating sequence of  FIG. 10  may be provided by the system of  FIGS. 1A and 1B  including the method of  FIG. 9  as executable instructions. 
     The first plot from the top of  FIG. 10  is a plot of particulate matter load or an amount of particulate matter stored in a particulate filter versus time. The vertical axis represents particulate matter load and particulate matter load increases in the direction of the vertical axis arrow. The horizontal axis represents time and time increases from the right side of the plot to the left side of the plot. Horizontal line  1002  represents a threshold particulate filter load above which it may be desirable to reduce particulate formation by the engine. 
     The second plot from the top of  FIG. 10  is a plot of particulate matter purge state versus time. The particulate matter filter is being purged of particulate matter when the trace is at a higher level near the vertical axis arrow. The particulate matter filter is not being purged of particulate matter when the trace is at a lower level near the horizontal axis. The horizontal axis represents time and time increases from the right side of the plot to the left side of the plot. 
     The third plot from the top of  FIG. 10  is a plot of the particulate matter environment in which the engine and vehicle are operating. The vertical axis represents particulate environment. The engine and vehicle are operating in a low particulate environment when the trace is at a higher level near the vertical axis arrow. The engine and vehicle are operating in a higher or nominal particulate environment when the trace is at a lower level near the horizontal axis. The horizontal axis represents time and time increases from the right side of the plot to the left side of the plot. 
     The fourth plot from the top of  FIG. 10  is a plot of port fuel injector (PFI) fuel injection fraction versus time. The vertical axis represents PFI fuel injection fuel fraction and the PFI fuel injection fraction increases in the direction of the vertical axis arrow. The horizontal axis represents time and time increases from the right side of the plot to the left side of the plot. 
     At time T 5 , the particulate filter load is less than threshold  1002  and increasing. The particulate filter is not being purged as is indicated by the low particulate filter purge state trace. The vehicle and engine are operating in a nominal particulate environment and the port fuel injection (PFI) fraction is at a middle level. 
     At time T 6 , the particulate filter load exceeds threshold  1002  as the engine continues to produce particulate matter. The PFI injection fraction is increased and the direct fuel injection fraction is decreased (not shown) so that the engine operates with the same air-fuel ratio, but with a greater fraction of port injected fuel. The particulate environment is nominal and the particulate filter is not being purged. 
     At time T 7 , the particulate filter starts being purged. The particulate filter may be purged when the engine achieves a predetermined speed and desired torque or other specified conditions. The particulate matter filter may be purged via increasing a temperature of the particulate filter via retarding engine spark timing. The particulate filter load is decreased in response to the particulate filter entering purge mode. The particulate matte environment is nominal and the PFI injection fraction remains at an increased fraction. 
     At time T 8 , the particulate filter load has decreased to a lower level. The particulate filter exits purge mode in response to the low particulate filter load and PFI injection fraction is decreased. The vehicle continues to operate in a nominal particulate environment. It should be noted that in other examples the PFI injection fraction may be reduces as soon as the particulate load is less than threshold  1002 . 
     At time T 9 , the vehicle and engine enter a low particulate environment such as an enclosed building or urban area as indicated by the particulate environment trace transitioning to a higher level. The particulate filter load remains low and the particulate filter is not being purged. The PFI fraction is increased and the direct injection fraction is decreased to maintain engine air-fuel ratio and reduce particulate formation within the engine. In this way, the engine air-fuel ratio may remain a same value for a same engine speed and driver demand. 
     At time T 10 , the vehicle and engine exit the low particulate environment and the particulate environment trace transitions to a lower level. The particulate filter load remains low and the particulate filter is not being purged. The PFI fraction is decreased and the direct injection fraction is increased to improve cylinder charge cooling. Thus, the direct fuel injection fraction may be increased and the port fuel injection fraction may be decreased when the vehicle is operating in a nominal particulate environment so that higher engine torque levels may be achieved. 
     Referring now to  FIG. 11 , an example method for compensating port fuel injector degradation is shown. The method of  FIG. 11  may provide the operating sequence shown in  FIG. 12 . Additionally, at least portions of the method of  FIG. 11  may be included as executable instructions in the system of  FIGS. 1A and 1B . Further, portions of the method of  FIG. 11  may be actions taken by controller  12  in the physical world to transform vehicle operating conditions. 
     At  1102 , method  1100  judges whether or not the port fuel injector degradation or reduced performance is present. Further, if port injector degradation is determined, method  1100  may determine the particular port fuel injector that is degraded. In one example, method  1100  may judge that port fuel injector degradation is present if engine air-fuel ratio is more than a predetermined air-fuel ratio away from a desired engine air-fuel ratio. Alternatively, method  1100  may judge whether or not there is port fuel injector degradation based on output of injector monitoring circuitry or an engine speed/position sensor (e.g., an increase or decrease of engine speed may be indicative of a change in injector performance). If method  1100  judges that port fuel injector degradation is present, the answer is yes and method  1100  proceeds to  1106 . Otherwise, the answer is no and method  1100  proceeds to  1104 . Method  1100  may determine a particular port injector is degraded based on output of the monitoring circuitry or engine air-fuel ratio at a particular engine crankshaft angle. 
     At  1104 , method  1100  operates all port fuel injectors and direct fuel injectors based on engine and vehicle operating conditions. The port and direct fuel injectors may inject different amounts of fuel at different times based on engine operating conditions. Method  1100  proceeds to exit after all port and direct fuel injectors are operated. 
     At  1106 , method  1100  judges whether direct fuel injector degradation is present. In one example, method  1100  may judge that direct fuel injector degradation is present if engine air-fuel ratio is more than a predetermined air-fuel ratio away from a desired engine air-fuel ratio. For example, if only direct fuel injectors are activated at a particular engine speed and desired torque, direct fuel injector degradation may be determined if the engine air-fuel ratio is not equivalent to a desired engine air-fuel ratio. Alternatively, method  1100  may judge whether or not there is direct fuel injector degradation based on output of injector monitoring circuitry. If method  1100  judges that direct fuel injector degradation is present, the answer is yes and method  1100  proceeds to  1108 . Otherwise, the answer is no and method  1100  proceeds to  1112 . 
     At  1108 , method  1100  deactivates a direct injector supplying fuel to a same cylinder as a port fuel injector that is determined to be degraded. Further, the degraded port fuel injector is deactivated by not sending fuel injection pulse widths to the degraded port fuel injector. The direct fuel injector is deactivated so that the remaining cylinders may operate with both port and direct injectors to produce torque and emissions that are consistent between cylinders as compared to operating the engine with one cylinder using direct injection and the remaining cylinders using port and direct injection. Thus, one or more cylinders experiencing port injector degradation are deactivated by not injecting fuel in the cylinder with port fuel injector degradation. Method  1100  proceeds to  1110  after selected cylinders are deactivated. 
     At  1110 , method  1100  increases torque output of at least one of the remaining active cylinders to provide the desired desired torque. By deactivating one or more engine cylinders at  1108 , engine torque may be reduced. Therefore, the decrease in engine torque may be compensated by increasing torque in one or more of the remaining engine cylinders. The torque provided by the remaining cylinders may be increased by opening the engine throttle and increasing fuel supplied to the active cylinder. Further, the maximum engine torque may be limited to a lower value as compared to if injector degradation of reduced performance is not present. Method  1100  proceeds to exit after torque output of one or more active cylinder is increased. 
     At  1112 , method  1100  deactivates all port fuel injectors and supplies fuel to all engine cylinders via only direct fuel injectors. All port fuel injectors are deactivated so that each cylinder produces torque and emissions similar to other engine cylinders. In this way, all engine cylinders may operate similarly instead of one group of cylinders providing different output as compared to other engine cylinders. Method  1100  proceeds to  1114  after all port fuel injector are deactivated. 
     At  1114 , method  1100  adjusts fuel injector timing of direct fuel injectors. The direct fuel injector timing is adjusted to increase an amount of fuel supplied by the direct fuel injectors so that the engine provides a same amount of torque at a particular engine speed and desired torque as when the engine is operated with both port and direct fuel injection. Further, the direct fuel injector timing may be adjusted to reduce particulate formation within the engine. Method  1100  proceeds to exit after direct fuel injector timing is adjusted. 
     In this way, fuel injector operation may be adjusted during conditions of port fuel injector degradation to improve engine emissions and torque production. By deactivating all engine port fuel injectors when a single or sole port fuel injector is degraded, the engine may be operated to provide more consistent torque and emissions via the active engine cylinders. 
     Referring now to  FIG. 12 , an example operating sequence according to the method of  FIG. 11  is shown. The operating sequence of  FIG. 12  may be provided by the system of  FIGS. 1A and 1B  including the method of  FIG. 11  as executable instructions. 
     The first plot from the top of  FIG. 12  is a plot of cylinder number one port fuel injector state versus time. The vertical axis represents cylinder number one port fuel injector state. Cylinder number one port fuel injector is operating within nominal specifications when the trace is at a higher level near the vertical axis arrow. Cylinder number one port fuel injector is operating at degraded conditions when the trace is a near the horizontal axis. Port injector degradation may be caused by port fuel injector electrical degradation or mechanical degradation. Further, port fuel injector degradation may be caused by a lack of fuel being supplied to the port fuel injector. The horizontal axis represents time and time increases from the right side of the plot to the left side of the plot. 
     The second plot from the top of  FIG. 12  is a plot of cylinder number one direct fuel injector state versus time. The vertical axis represents cylinder number one direct fuel injector state. Cylinder number one direct fuel injector is operating within nominal specifications when the trace is at a higher level near the vertical axis arrow. Cylinder number one direct fuel injector is operating at degraded conditions when the trace is a near the horizontal axis. Direct injector degradation may be caused by direct fuel injector electrical degradation or mechanical degradation. Further, direct fuel injector degradation may be caused by a lack of fuel being supplied to the direct fuel injector. The horizontal axis represents time and time increases from the right side of the plot to the left side of the plot. 
     The third plot from the top of  FIG. 12  is a plot of engine port fuel injector (PFI) state versus time. The vertical axis represents engine port fuel injector state. Engine port fuel injectors may be active when the trace is at a higher level near the vertical axis arrow. Engine port fuel injectors are not active when the trace is a near the horizontal axis. The engine port fuel injector state is an overall indication of the engine&#39;s port injectors being active or inactive; however, particular port fuel injectors may be deactivated even when the engine port fuel injector state indicates active. All engine port fuel injectors are deactivated when the engine port fuel injector state indicates deactivated. The horizontal axis represents time and time increases from the right side of the plot to the left side of the plot. 
     The fourth plot from the top  FIG. 12  is a plot of engine direct fuel injector state versus time. The vertical axis represents engine direct fuel injector state. Engine direct fuel injectors may be active when the trace is at a higher level near the vertical axis arrow. Engine direct fuel injectors are not active when the trace is a near the horizontal axis. The engine direct fuel injector state is an overall indication of the engine&#39;s direct injectors being active or inactive; however, particular direct fuel injectors may be deactivated even when the engine direct fuel injector state indicates active. All engine direct fuel injectors are deactivated when the engine direct fuel injector state indicates deactivated. The horizontal axis represents time and time increases from the right side of the plot to the left side of the plot. 
     At time T 15 , the engine port and direct fuel injectors are indicated as being active. Further, the port and direct fuel injectors for cylinder number one are active. Fuel may be injected via port and direct fuel injectors when the fuel injectors are active. 
     At time T 16 , the port fuel injector of cylinder number one is indicated as degraded as indicated by the PFI injector state for cylinder number one transitioning to a lower level. The PFI injector may be degraded if more or less fuel than is desired is or is not injected by the PFI injector. All engine port fuel injectors are deactivated shortly thereafter in response to the port fuel injector of cylinder number one being degraded. No direct fuel injectors are deactivated as indicated by the direct fuel injector state trace being at a higher level and the cylinder number one direct injector state being at a higher level. By deactivating all engine port fuel injectors, it may be possible to have cylinders that operate similarly and provide similar amount of torque and emissions. If all port fuel injectors were not deactivated, some engine cylinders may output different torque and emissions as compared to other engine cylinders operating with similar operating conditions. 
     At time T 17 , the cylinder number one direct fuel injector state transitions to a lower level to indicate degradation of cylinder number one&#39;s direct fuel injector. Therefore, port fuel injectors that are not degraded are reactivated and both the direct and port fuel injectors of cylinder number one are deactivated shortly thereafter. The direct fuel injectors of engine cylinders other than cylinder number one remain active. Consequently, port and direct fuel injectors of cylinder number one are deactivated while port and direct fuel injectors of other cylinders remain activated. In this way, port fuel injectors may be operated to provide more consistent engine torque and emissions between different engine cylinders. 
     Referring now to  FIG. 13 , an example method for compensating direct fuel injector degradation is shown. The method of  FIG. 13  may provide the operating sequence shown in  FIG. 14 . Additionally, at least portions of the method of  FIG. 13  may be included as executable instructions in the system of  FIGS. 1A and 1B . Further, portions of the method of  FIG. 13  may be actions taken by controller  12  in the physical world to transform vehicle operating conditions. 
     At  1302 , method  1300  judges whether or not the direct fuel injector degradation or reduced performance is present. Further, if direct injector degradation is determined, method  1300  may determine the particular direct fuel injector that is degraded. In one example, method  1300  may judge that direct fuel injector degradation is present if engine air-fuel ratio is more than a predetermined air-fuel ratio away from a desired engine air-fuel ratio. Alternatively, method  1300  may judge whether or not there is direct fuel injector degradation based on output of injector monitoring circuitry. If method  1300  judges that direct fuel injector degradation is present, the answer is yes and method  1300  proceeds to  1306 . Otherwise, the answer is no and method  1300  proceeds to  1304 . Method  1300  may determine a particular direct injector is degraded based on output of the monitoring circuitry or engine air-fuel ratio at a particular engine crankshaft angle. 
     At  1304 , method  1300  operates all port fuel injectors and direct fuel injectors based on engine and vehicle operating conditions. The port and direct fuel injectors may inject different amounts of fuel at different times based on engine operating conditions. Method  1300  proceeds to exit after all port and direct fuel injectors are operated. 
     At  1306 , method  1300  deactivates a port fuel injector that supplies fuel to a same engine cylinder that is supplied fuel by the degraded direct fuel injector. The port fuel injector is deactivated by not sending fuel injector pulse widths to the port fuel injector. Further, the degraded direct fuel injector is deactivated by not sending fuel injector pulse widths to the degraded direct fuel injector. Method  1300  proceeds to  1308  after the degraded direct fuel injector and its associated port fuel injector (e.g., port fuel injector that supplies fuel to a same cylinder as the direct fuel injector) are deactivated. 
     At  1308 , method  1300  judges if the direct fuel injector degradation affects a paired direct injector. A paired direct injector is a direct injector that supplies fuel to a different cylinder than the cylinder that is supplied fuel by the degraded direct fuel injector via a single fuel injector driver. The single fuel injector driver may individually supply current two different fuel injectors. Thus, the fuel injector supplies a pair of fuel injectors. If method  1300  judges that the direct fuel injector degradation affects a paired direct injector (e.g., a direct injector that shares a fuel injector driver with the degraded direct fuel injector), the answer is yes and method  1300  proceeds to  1310 . Otherwise, the answer is no and method  1300  proceeds to  1312 . 
     At  1310 , method  1300  deactivates the direct fuel injector that is paired with the degraded direct injector at a fuel injector driver. Further, the port fuel injector supplying fuel to the cylinder the paired direct fuel injector supplies fuel to is deactivated. Thus, two cylinders are deactivated. Additionally, torque provided by the remaining cylinders may be increased by opening the engine throttle and increasing fuel supplied to the remaining active cylinders. Further, maximum engine torque may be limited to less than a maximum engine torque if fuel injector degradation is not present. The maximum engine torque may be limited via limiting throttle opening. Method  1300  proceeds to exit after the paired direct fuel injector is deactivate and torque output of active cylinders is increased. 
     At  1312 , method  1300  operates the port and direct fuel injectors in cylinders remaining active in response to vehicle and engine operating conditions. Further, torque output of at least one cylinder is increased to compensate for torque lost by deactivating the cylinder exhibiting direct fuel injector degradation. Torque of an engine cylinder may be increased via increasing air and fuel flow to the cylinder. Method  1300  proceeds to exit after the remaining cylinder port and direct fuel injectors are operated based on engine and vehicle operating conditions. 
     In this way, fuel injector operation may be adjusted during conditions of direct fuel injector degradation to improve engine emissions and torque production. By a port fuel injector that injects fuel to a same cylinder as a degraded direct fuel injector, it may be possible to reduce the possibility of further degradation to the degraded direct fuel injector. 
     Referring now to  FIG. 14 , an example operating sequence according to the method of  FIG. 13  is shown. The operating sequence of  FIG. 14  may be provided by the system of  FIGS. 1A and 1B  including the method of  FIG. 13  as executable instructions. 
     The first plot from the top of  FIG. 14  is a plot of cylinder number one port fuel injector state versus time. The vertical axis represents cylinder number one port fuel injector state. Cylinder number one port fuel injector is operating within nominal specifications when the trace is at a higher level near the vertical axis arrow. Cylinder number one port fuel injector is operating at degraded conditions when the trace is a near the horizontal axis. Port injector degradation may be caused by port fuel injector electrical degradation or mechanical degradation. Further, port fuel injector degradation may be caused by a lack of fuel being supplied to the port fuel injector. The horizontal axis represents time and time increases from the right side of the plot to the left side of the plot. 
     The second plot from the top of  FIG. 14  is a plot of cylinder number one direct fuel injector state versus time. The vertical axis represents cylinder number one direct fuel injector state. Cylinder number one direct fuel injector is operating within nominal specifications when the trace is at a higher level near the vertical axis arrow. Cylinder number one direct fuel injector is operating at degraded conditions when the trace is a near the horizontal axis. Direct injector degradation may be caused by direct fuel injector electrical degradation or mechanical degradation. Further, direct fuel injector degradation may be caused by a lack of fuel being supplied to the direct fuel injector. The horizontal axis represents time and time increases from the right side of the plot to the left side of the plot. 
     The third plot from the top of  FIG. 14  is a plot of engine port fuel injector (PFI) state versus time. The vertical axis represents engine port fuel injector state. Engine port fuel injectors may be active when the trace is at a higher level near the vertical axis arrow. Engine port fuel injectors are not active when the trace is a near the horizontal axis. The engine port fuel injector state is an overall indication of the engine&#39;s port injectors being active or inactive; however, particular port fuel injectors may be deactivated even when the engine port fuel injector state indicates active. All engine port fuel injectors are deactivated when the engine port fuel injector state indicates deactivated. The horizontal axis represents time and time increases from the right side of the plot to the left side of the plot. 
     The fourth plot from the top  FIG. 14  is a plot of engine direct fuel injector state versus time. The vertical axis represents engine direct fuel injector state. Engine direct fuel injectors may be active when the trace is at a higher level near the vertical axis arrow. Engine direct fuel injectors are not active when the trace is a near the horizontal axis. The engine direct fuel injector state is an overall indication of the engine&#39;s direct injectors being active or inactive; however, particular direct fuel injectors may be deactivated even when the engine direct fuel injector state indicates active. All engine direct fuel injectors are deactivated when the engine direct fuel injector state indicates deactivated. The horizontal axis represents time and time increases from the right side of the plot to the left side of the plot. 
     At time T 20 , the engine port and direct fuel injectors are indicated as being active. Further, the port and direct fuel injectors for cylinder number one are active. Fuel may be injected via port and direct fuel injectors when the fuel injectors are active. 
     At time T 21 , the direct fuel injector of cylinder number one is indicated as degraded as indicated by the direct injector state for cylinder number one transitioning to a lower level. The direct fuel injector may be degraded if more or less fuel than is desired is or is not injected by the direct fuel injector. Shortly thereafter, a port fuel injector supplying fuel to cylinder number one is deactivated by not sending a fuel pulse width to the port fuel injector. The port fuel injector for cylinder number one is indicated as not being degraded. The port fuel injectors and direct fuel injectors of other engine cylinders remain active. Further, torque output of active cylinders may be increased to compensate for the loss in torque production from cylinder number one. 
     In this way, engine torque production may be maintained if a cylinder is deactivated due to direct fuel injector degradation. Further, the port fuel injector supplying fuel to a same cylinder as a degraded direct fuel injector is deactivated so that temperatures in the cylinder may not rise to further degrade the direct fuel injector. 
     Thus, the methods of  FIGS. 2, 4, 6, 7, 9, 11, and 13  provide for an engine fueling method, comprising: receiving inputs to a controller; and deactivating all port fuel injectors of an engine in response to reduced performance of a sole port fuel injector based on the inputs to the controller. The method includes where the inputs include an oxygen sensor. The method includes where the inputs include a fuel injector driver. The method includes where the inputs include an engine position sensor. The method includes where deactivating all port fuel injector includes ceasing to provide a pulse width to all port fuel injectors. 
     In some examples, the method further comprises increasing amounts of fuel injected by all direct fuel injectors of the engine in response to the degradation of the sole port fuel injector. The method further comprises limiting engine torque to less than a threshold torque in response to the degradation of the sole port fuel injector. 
     In some examples, the methods provide for an engine fueling method, comprising: receiving inputs to a controller to determine reduced fuel injector performance; deactivating a direct fuel injector of a first cylinder via the controller in response to reduced performance of a port fuel injector of the first cylinder when reduced performance of at least one of an engine&#39;s direct fuel injectors is present; and deactivating all of an engine&#39;s port fuel injectors via the controller in response to reduced performance of a sole port fuel injector when no reduced performance of all of the engine&#39;s direct fuel injectors is present. 
     The method includes where the reduced fuel injector performance is based on output of an oxygen sensor. The method includes where the reduced fuel injector performance is based on an engine position sensor. The method includes where the direct fuel injector is deactivated via ceasing to supply a pulse width to the direct fuel injector. The method further comprises adjusting output of one or more cylinders in response to an indication of reduced fuel injector performance. The method further comprises limiting engine torque to a threshold torque in response to the indication of reduced fuel injector performance. The method includes where the reduced performance is based on output of a paired fuel injector driver. 
     As will be appreciated by one of ordinary skill in the art, the methods described in  FIGS. 2, 4, 6, 7, 9, 11, and 13  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 steps 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 objects, features, and advantages described herein, but is provided for ease of illustration and description. Although not explicitly illustrated, one of ordinary skill in the art will recognize that one or more of the illustrated steps or functions may be repeatedly performed depending on the particular strategy being used. Further, the methods described herein may be a combination of actions taken by a controller in the physical world and instructions within the controller. At least portions of 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. 
     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, single cylinder, I2, I3, I4, I5, V6, V8, V10, V12 and V16 engines operating in natural gas, gasoline, diesel, or alternative fuel configurations could use the present description to advantage.