Patent Publication Number: US-10767599-B2

Title: Systems and methods for onboard canister purge valve flow mapping

Description:
FIELD 
     The present description relates generally to methods and systems for onboard flow mapping of a canister purge valve configured to regulate a flow of purge gasses from a fuel vapor storage canister to an engine of a vehicle. 
     BACKGROUND/SUMMARY 
     Vehicle evaporative emission control systems may be configured to store fuel vapors from fuel tank refueling and diurnal engine operations in a fuel vapor canister containing a suitable adsorbent, and then purge the stored vapors during a subsequent engine operation. The stored vapors may be routed to an engine intake for combustion, further improving fuel economy. 
     In a canister purge operation, a canister purge valve coupled between the engine intake and the fuel canister is opened, allowing for intake manifold vacuum to be applied to the fuel canister. On a boosted engine, that vacuum draw may be supplied via an ejector during boosted operation. For particular hybrid vehicles, that vacuum draw may be provided via a canister purge pump positioned between the canister and the canister purge valve, for example. Simultaneously, a canister vent valve coupled between the fuel canister and atmosphere is opened, allowing for fresh air to enter the canister. Further, in some examples a vapor blocking valve coupled between the fuel tank and the fuel canister is closed to prevent the flow of fuel vapors from the fuel tank to the engine. This configuration facilitates desorption of stored fuel vapors from the adsorbent material in the canister, regenerating the adsorbent material for further fuel vapor adsorption. 
     A flow map stored at a controller of a vehicle may be used to command an appropriate duty cycle for the canister purge valve when purging of the canister is requested. More specifically, a particular flow value may be commanded in response to a request to purge the canister, and a  3 D flow map stored at the controller may be queried to determine an appropriate duty cycle for the canister purge valve as a function of engine manifold vacuum. Such a flow value may be chosen so as to avoid potentially stalling the engine due to a rich amount of fuel vapors emanating from the canister (and fuel tank in some examples), and may be further based on a number of other relevant engine operating parameters. Furthermore, it is desirable to learn canister loading state via feedback from exhaust gas oxygen sensors during purging operations, and in order to accurately learn such a loading state, it is imperative that the commanded flow is accurate. If the canister purge valve has become degraded to any extent (or replaced), such a commanded flow value may not be accurate or representative, which may thus impair accurate learning of canister loading state. An inability to accurately assess canister loading state may adversely impact engine operation. 
     Such flow maps for canister purge valves may be generated via a technician offline, and are not updated via any onboard diagnostic protocol. More specifically, at a bench, a flow meter may be used via a technician to assess flow values for a canister purge valve at various vacuum levels to generate a flow map for use when the vehicle is in operation. However, as discussed above, canister purge valves may become degraded or may be in some examples replaced (with a valve having different flow characteristics), thus rendering the use of a particular flow map stored at the controller non-ideal. However, evaporative emissions systems for vehicles that include fuel vapor storage canisters and canister purge valves are not equipped with flow meters or onboard strategy to update canister purge valve flow maps as a function of an operational state of the canister purge valve (e.g. unable to properly seal when commanded closed, etc.). An inability to update such flow maps as a function of canister purge valve operational state may impact engine operation as discussed. Thus, an onboard diagnostic strategy to periodically, or in response to an indication of canister purge valve degradation, update such flow maps to more accurately reflect flow characteristics of the canister purge valve, is lacking. 
     The inventors herein have recognized the above-mentioned issues, and have developed systems and methods to address them. In one example, a method comprises controlling a duty cycle of a purge valve configured to regulate a purge flow from a fuel vapor storage canister to an intake of an engine during a canister purging event based on a degradation factor obtained by comparison of durations at which a predetermined pressure is reached in an evaporative emissions system at multiple purge valve activation levels. In this way, the purge valve may be controlled to avoid engine hesitation, stall, or other undesired engine operating conditions, during conditions where the canister is purged of fuel vapors to engine intake. 
     In one example, the evaporative emissions system is sealed for obtaining the durations at which the predetermined pressure is reached, the predetermined pressure comprises a negative pressure with respect to atmospheric pressure, and a fuel system is sealed from the evaporative emissions system for obtaining the durations at which the predetermined pressure is reached. 
     As another example, the comparison of the durations at which the predetermined pressure is reached at multiple purge valve activation levels includes both conditions for which there is an absence of evaporative emissions system degradation and conditions for which there is a presence of evaporative emissions system degradation. 
     As another example, such a method further comprises operating a pump positioned downstream of the fuel vapor storage canister to communicate a predetermined vacuum to the evaporative emissions system for obtaining the durations at which the predetermined pressure is reached. In one example the pump comprises the engine, and in another example the pump comprises a purge pump positioned in a purge line between the purge valve and the fuel vapor storage canister. 
     As yet another example, the predetermined pressure that is reached is monitored via a pressure sensor positioned in the evaporative emissions system configured to indicate pressure across a reference orifice in the evaporative emissions system. The multiple purge valve activation levels may include two or more different duty cycles of the purge valve. Furthermore, the degradation factor may be used to adjust a flow map for controlling the duty cycle of the purge valve during the canister purging event. 
     The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings. 
     It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  schematically shows an example vehicle propulsion system. 
         FIG. 2  schematically shows an example vehicle system comprising an engine system coupled to a fuel system and an evaporative emissions system. 
         FIG. 3A  shows a schematic depiction of an evaporative level check module (ELCM) in a configuration to perform a reference check. 
         FIG. 3B  shows a schematic depiction of an ELCM in a configuration to evacuate a fuel system and/or evaporative emissions system. 
         FIG. 3C  shows a schematic depiction of an ELCM in a configuration that couples a fuel vapor canister to atmosphere. 
         FIG. 3D  shows a schematic depiction of an ELCM in a configuration to pressurize a fuel system and/or evaporative emissions system. 
         FIG. 3E  shows a schematic depiction of an ELCM in a configuration to seal an evaporative emissions system from atmosphere. 
         FIG. 4  schematically shows a single cylinder of the engine system of  FIGS. 1-2 . 
         FIG. 5A  schematically depicts a purge flow rate as a function of a duty cycle of a CPV and intake manifold vacuum level. 
         FIG. 5B  schematically depicts a purge flow rate as a function of a duty cycle of a CPV and a purge pump speed. 
         FIG. 5C  corresponds to  FIG. 5A , and further illustrates the purge flow rates of  FIG. 5A  in the presence of degradation. 
         FIG. 5D  corresponds to  FIG. 5B , and further illustrates the purge flow rates of  FIG. 5B  in the presence of degradation. 
         FIG. 6  depicts an example CPV flow map stored at a controller of a vehicle. 
         FIG. 7A  schematically depicts onboard data obtained for updating a CPV flow map stored at the controller, where the data is obtained via evacuating an evaporative emissions system via intake manifold vacuum. 
         FIG. 7B  schematically depicts onboard data obtained for updating a CPV flow map stored at the controller, where the data is obtained via evacuating an evaporative emissions system via a purge pump. 
         FIG. 8  depicts a high-level example method for adjusting a CPV flow map stored at a controller of a vehicle, by obtaining baseline onboard CPV flow data and test onboard CPV flow data. 
         FIG. 9  depicts an example method for obtaining the baseline and/or test CPV flow data of  FIG. 8  using intake manifold vacuum while the engine is combusting air and fuel. 
         FIG. 10  continues from  FIG. 9 , and depicts an example method for obtaining the baseline and/or test CPV flow data of  FIG. 8  using a purge pump. 
         FIG. 11  continues from  FIG. 10 , and depicts an example method for obtaining the baseline and/or test CPV flow data of  FIG. 8  using intake manifold vacuum via the rotating the engine unfueled. 
         FIG. 12  depicts an example timeline for obtaining CPV flow data via the method of  FIG. 9 . 
         FIG. 13  depicts an example timeline for obtaining CPV flow data via the method of  FIG. 10 . 
         FIG. 14  depicts an example timeline for obtaining CPV flow data via the method of  FIG. 11 . 
         FIG. 15  depicts a high-level example method for indicating evaporative emissions system degradation during a refueling event by monitoring fluid flow in the intake of an engine. 
         FIG. 16  depicts an example method for obtaining baseline and test evap flow measurements for use with the method of  FIG. 15 . 
         FIG. 17  depicts an example timeline for obtaining the baseline and test evap flow measurements for use with the method of  FIG. 15 , according to the method of  FIG. 16 . 
         FIG. 18  depicts a high-level example method for indicating evaporative emissions system degradation during a key-off event that does not include a refueling event, by monitoring fluid flow in the intake of an engine. 
         FIG. 19  depicts an example method for obtaining baseline and test evap flow measurements for use with the method of  FIG. 18 . 
         FIG. 20  depicts an example timeline for obtaining the baseline and test evap flow measurements for use with the method of  FIG. 18 , according to the method of  FIG. 19 . 
     
    
    
     DETAILED DESCRIPTION 
     The following description relates to systems and methods for controlling purging of a fuel vapor storage canister positioned in an evaporative emissions system of a vehicle, based on indications as to whether the evaporative emissions system and/or components therein are degraded. The systems and methods include using onboard diagnostics to indicate evaporative emissions system degradation, and for updating flow maps stored at the controller that are used to control a duty cycle of a canister purge valve during purging events, in response to said degradation. The systems and methods may in some examples be conducted under conditions where an engine of the vehicle is not combusting air and fuel. Accordingly, such systems and methods relate to hybrid electric vehicles, such as the hybrid electric vehicle system of  FIG. 1 .  FIG. 2  provides details of an engine system selectively coupled to an evaporative emissions system and fuel system. The evaporative emissions system may include a pump positioned in a vent line, where the pump may be controlled under various scenarios as illustrated at  FIGS. 3A-3E . An example of a cylinder of the engine is depicted at  FIG. 4 . 
       FIGS. 5A-5B  depict examples of purge flow rates as a function of a duty cycle of the canister purge valve, and  FIGS. 5C-5D  depict how such flow rates may be impacted by degradation of the canister purge valve and/or other components of the evaporative emissions system (e.g. canister internal filter being clogged, sources of undesired evaporative emissions). An example of a flow map stored at a controller that is used to control the duty cycle of the canister purge valve for purging the canister is depicted at  FIG. 6 .  FIGS. 7A-7B  graphically illustrate onboard methodology for updating such a flow map as that depicted at  FIG. 6 .  FIG. 8  depicts a high-level example method for updating/adjusting such a flow map, and for controlling future purging events of the canister based on the updated flow map.  FIG. 9  illustrates a method for obtaining data used to update a flow map via methodology that relies on the engine combusting air and fuel.  FIG. 10  illustrates a method that relies on a purge pump positioned between the engine and the canister, for obtaining data used to update a flow map.  FIG. 11  illustrates a method that relies on unfueled engine rotation to obtain data used to update a flow map.  FIG. 12  depicts an example timeline for obtaining data for updating a flow map according to the method of  FIG. 9 .  FIG. 13  depicts an example timeline for obtaining data for updating a flow map according to the method of  FIG. 10 .  FIG. 14  depicts an example timeline for obtaining data for updating a flow map according to the method of  FIG. 11 . 
       FIG. 15  depicts a high-level method for providing an indication of a presence or absence of degradation stemming from the evaporative emissions system during a refueling event.  FIG. 16  illustrates onboard methodology for obtaining data for use with the method of  FIG. 15 .  FIG. 17  depicts an example timeline for obtaining such data according to  FIG. 16 , for indicating a presence or absence of degradation according to  FIG. 15 .  FIG. 18  depicts a high-level example method for providing an indication of a presence or absence of degradation stemming from the evaporative emissions system during a key-off condition that does not include a refueling event.  FIG. 19  illustrates onboard methodology for obtaining data for use with the method of  FIG. 18 .  FIG. 20  depicts an example timeline for obtaining such data according to  FIG. 19 , for indicating a presence or absence of degradation according to  FIG. 18 . 
     Turning now to the figures,  FIG. 1  illustrates an example vehicle propulsion system  100 . Vehicle propulsion system  100  includes a fuel burning engine  110  and a motor  120 . As a non-limiting example, engine  110  comprises an internal combustion engine and motor  120  comprises an electric motor. Motor  120  may be configured to utilize or consume a different energy source than engine  110 . For example, engine  110  may consume a liquid fuel (e.g., gasoline) to produce an engine output while motor  120  may consume electrical energy to produce a motor output. As such, a vehicle with propulsion system  100  may be referred to as a hybrid electric vehicle (HEV). 
     Vehicle propulsion system  100  may utilize a variety of different operational modes depending on operating conditions encountered by the vehicle propulsion system. Some of these modes may enable engine  110  to be maintained in an off state (i.e. set to a deactivated state) where combustion of fuel at the engine is discontinued. For example, under select operating conditions, motor  120  may propel the vehicle via drive wheel  130  as indicated by arrow  122  while engine  110  is deactivated. 
     During other operating conditions, engine  110  may be set to a deactivated state (as described above) while motor  120  may be operated to charge energy storage device  150 . For example, motor  120  may receive wheel torque from drive wheel  130  as indicated by arrow  122  where the motor may convert the kinetic energy of the vehicle to electrical energy for storage at energy storage device  150  as indicated by arrow  124 . This operation may be referred to as regenerative braking of the vehicle. Thus, motor  120  can provide a generator function in some embodiments. However, in other embodiments, generator  160  may instead receive wheel torque from drive wheel  130 , where the generator may convert the kinetic energy of the vehicle to electrical energy for storage at energy storage device  150  as indicated by arrow  162 . 
     During still other operating conditions, engine  110  may be operated by combusting fuel received from fuel system  140  as indicated by arrow  142 . For example, engine  110  may be operated to propel the vehicle via drive wheel  130  as indicated by arrow  112  while motor  120  is deactivated. During other operating conditions, both engine  110  and motor  120  may each be operated to propel the vehicle via drive wheel  130  as indicated by arrows  112  and  122 , respectively. A configuration where both the engine and the motor may selectively propel the vehicle may be referred to as a parallel type vehicle propulsion system. Note that in some embodiments, motor  120  may propel the vehicle via a first set of drive wheels and engine  110  may propel the vehicle via a second set of drive wheels. 
     In other embodiments, vehicle propulsion system  100  may be configured as a series type vehicle propulsion system, whereby the engine does not directly propel the drive wheels. Rather, engine  110  may be operated to power motor  120 , which may in turn propel the vehicle via drive wheel  130  as indicated by arrow  122 . For example, during select operating conditions, engine  110  may drive generator  160 , which may in turn supply electrical energy to one or more of motor  120  as indicated by arrow  114  or energy storage device  150  as indicated by arrow  162 . As another example, engine  110  may be operated to drive motor  120  which may in turn provide a generator function to convert the engine output to electrical energy, where the electrical energy may be stored at energy storage device  150  for later use by the motor. 
     Fuel system  140  may include one or more fuel storage tanks  144  for storing fuel on-board the vehicle. For example, fuel tank  144  may store one or more liquid fuels, including but not limited to: gasoline, diesel, and alcohol fuels. In some examples, the fuel may be stored on-board the vehicle as a blend of two or more different fuels. For example, fuel tank  144  may be configured to store a blend of gasoline and ethanol (e.g., E10, E85, etc.) or a blend of gasoline and methanol (e.g., M10, M85, etc.), whereby these fuels or fuel blends may be delivered to engine  110  as indicated by arrow  142 . Still other suitable fuels or fuel blends may be supplied to engine  110 , where they may be combusted at the engine to produce an engine output. The engine output may be utilized to propel the vehicle as indicated by arrow  112  or to recharge energy storage device  150  via motor  120  or generator  160 . 
     In some embodiments, energy storage device  150  may be configured to store electrical energy that may be supplied to other electrical loads residing on-board the vehicle (other than the motor), including cabin heating and air conditioning, engine starting, headlights, cabin audio and video systems, etc. As a non-limiting example, energy storage device  150  may include one or more batteries and/or capacitors. 
     Control system  190  may communicate with one or more of engine  110 , motor  120 , fuel system  140 , energy storage device  150 , and generator  160 . For example, control system  190  may receive sensory feedback information from one or more of engine  110 , motor  120 , fuel system  140 , energy storage device  150 , and generator  160 . Further, control system  190  may send control signals to one or more of engine  110 , motor  120 , fuel system  140 , energy storage device  150 , and generator  160  responsive to this sensory feedback. Control system  190  may receive an indication of an operator requested output of the vehicle propulsion system from a vehicle operator  102 . For example, control system  190  may receive sensory feedback from pedal position sensor  194  which communicates with pedal  192 . Pedal  192  may refer schematically to a brake pedal and/or an accelerator pedal. 
     Energy storage device  150  may periodically receive electrical energy from a power source  180  residing external to the vehicle (e.g., not part of the vehicle) as indicated by arrow  184 . As a non-limiting example, vehicle propulsion system  100  may be configured as a plug-in hybrid electric vehicle (HEV), whereby electrical energy may be supplied to energy storage device  150  from power source  180  via an electrical energy transmission cable  182 . During a recharging operation of energy storage device  150  from power source  180 , electrical transmission cable  182  may electrically couple energy storage device  150  and power source  180 . While the vehicle propulsion system is operated to propel the vehicle, electrical transmission cable  182  may disconnected between power source  180  and energy storage device  150 . Control system  190  may identify and/or control the amount of electrical energy stored at the energy storage device, which may be referred to as the state of charge (SOC). 
     In other embodiments, electrical transmission cable  182  may be omitted, where electrical energy may be received wirelessly at energy storage device  150  from power source  180 . For example, energy storage device  150  may receive electrical energy from power source  180  via one or more of electromagnetic induction, radio waves, and electromagnetic resonance. As such, it should be appreciated that any suitable approach may be used for recharging energy storage device  150  from a power source that does not comprise part of the vehicle. In this way, motor  120  may propel the vehicle by utilizing an energy source other than the fuel utilized by engine  110 . 
     Fuel system  140  may periodically receive fuel from a fuel source residing external to the vehicle. As a non-limiting example, vehicle propulsion system  100  may be refueled by receiving fuel via a fuel dispensing device  170  as indicated by arrow  172 . In some embodiments, fuel tank  144  may be configured to store the fuel received from fuel dispensing device  170  until it is supplied to engine  110  for combustion. In some embodiments, control system  190  may receive an indication of the level of fuel stored at fuel tank  144  via a fuel level sensor. The level of fuel stored at fuel tank  144  (e.g., as identified by the fuel level sensor) may be communicated to the vehicle operator, for example, via a fuel gauge or indication in a vehicle instrument panel  196 . 
     The vehicle propulsion system  100  may also include an ambient temperature/humidity sensor  198 , and a roll stability control sensor, such as a lateral and/or longitudinal and/or yaw rate sensor(s)  199 . The vehicle instrument panel  196  may include indicator light(s) and/or a text-based display in which messages are displayed to an operator. The vehicle instrument panel  196  may also include various input portions for receiving an operator input, such as buttons, touch screens, voice input/recognition, etc. For example, the vehicle instrument panel  196  may include a refueling button  193  which may be manually actuated or pressed by a vehicle operator to initiate refueling. For example, as described in more detail below, in response to the vehicle operator actuating refueling button  193 , a fuel tank in the vehicle may be depressurized so that refueling may be performed. 
     In an alternative example, the vehicle instrument panel  196  may communicate audio messages to the operator without display. Further, the sensor(s)  199  may include a vertical accelerometer to indicate road roughness. These devices may be connected to control system  190 . In one example, the control system may adjust engine output and/or the wheel brakes to increase vehicle stability in response to sensor(s)  199 . 
     Engine  110  may be configured with Start/Stop (S/S) feature  183  (also referred to herein as a S/S system) communicatively coupled to control system  190 , wherein the control system  190  may automatically shut down (idle-stop) the internal combustion engine  110 , without receiving operator input to shut down the engine, if selected idle-stop conditions are met. These may include, for example, torque demand being less than a threshold, engine speed less than a threshold engine speed, vehicle speed below a threshold vehicle speed (e.g. 5 mph) the onboard energy storage device being sufficiently charged, no request being received for air-conditioning, etc. Likewise, the engine may be automatically restarted responsive to the torque demand being higher than the threshold, the battery requesting to be charged, an air-conditioning compressor requesting to be operated, etc. In one example, the engine may be restarted responsive to the operator applying the accelerator pedal after being stopped for a duration (e.g. at a traffic signal). The engine may be cranked unfueled via motor  120  or a different motor coupled to a crankshaft of engine  110 , until a desired engine speed is reached, after which the motor may be disabled and engine fueling may be resumed. Thereafter engine combustion may be able to support engine spinning. As a result of the automatic start/stops, fuel consumption and exhaust emissions can be reduced. 
       FIG. 2  shows a schematic depiction of a vehicle system  206 . It may be understood that vehicle system  206  may be the same as vehicle propulsion system  100  described above at  FIG. 1 . The vehicle system  206  includes an engine system  208  coupled to an emissions control system  251  and a fuel system  218 . It may be understood that fuel system  218  may be the same as fuel system  140  depicted at  FIG. 1 . Emission control system  251  includes a fuel vapor container or canister  222  which may be used to capture and store fuel vapors. In some examples, vehicle system  206  may be a hybrid electric vehicle system. 
     The engine system  208  may include an engine  210  having a plurality of cylinders  230 . It may be understood that engine  210  may comprise the same engine as engine  110  depicted above at  FIG. 1 . The engine  210  includes an engine intake  223  and an engine exhaust  225 . The engine intake  223  includes a throttle  262  fluidly coupled to the engine intake manifold  244  via an intake passage  242 . Engine intake may further include various sensors. For example, a mass air flow (MAF) sensor  202  may be coupled to the engine intake to determine a rate of air mass or fluid flow flowing through the intake. Further, a barometric pressure sensor  213  may be included in the engine intake. For example, barometric pressure sensor  213  may be a manifold air pressure (MAP) sensor and may be coupled to the engine intake downstream of throttle  262 . Barometric pressure sensor  213  may rely on part throttle or full or wide open throttle conditions, e.g., when an opening amount of throttle  262  is greater than a threshold, in order accurately determine BP. 
     The engine exhaust  225  includes an exhaust manifold  248  leading to an exhaust passage  235  that routes exhaust gas to the atmosphere. The engine exhaust  225  may include one or more emission control devices  270 , which may be mounted in a close-coupled position in the exhaust. One or more emission control devices may include a three-way catalyst, lean NOx trap, diesel particulate filter, oxidation catalyst, etc. It will be appreciated that other components may be included in the engine such as a variety of valves and sensors. 
     Fuel system  218  may include a fuel tank  220  (e.g.  144 ) coupled to a fuel pump system  221 . The fuel pump system  221  may include one or more pumps for pressurizing fuel delivered to the injectors of engine  210 , such as the example injector  266  shown. While only a single injector  266  is shown, additional injectors are provided for each cylinder. It will be appreciated that fuel system  218  may be a return-less fuel system, a return fuel system, or various other types of fuel system. Fuel tank  220  may hold a plurality of fuel blends, including fuel with a range of alcohol concentrations, such as various gasoline-ethanol blends, including E10, E85, gasoline, etc., and combinations thereof. A fuel level sensor  234  located in fuel tank  220  may provide an indication of the fuel level (“Fuel Level Input”) to controller  212 . As depicted, fuel level sensor  234  may comprise a float connected to a variable resistor. Alternatively, other types of fuel level sensors may be used. 
     Vapors generated in fuel system  218  may be routed to an evaporative emissions control system  251  which includes a fuel vapor canister  222  via vapor recovery line  231 , before being purged to the engine intake  223 . Vapor recovery line  231  may be coupled to fuel tank  220  via one or more conduits and may include one or more valves for isolating the fuel tank during certain conditions. For example, vapor recovery line  231  may be coupled to fuel tank  220  via one or more or a combination of conduits  271 ,  273 , and  275 . 
     Further, in some examples, one or more fuel tank vent valves in conduits  271 ,  273 , or  275 . Among other functions, fuel tank vent valves may allow a fuel vapor canister of the emissions control system to be maintained at a low pressure or vacuum without increasing the fuel evaporation rate from the tank (which would otherwise occur if the fuel tank pressure were lowered). For example, conduit  271  may include a grade vent valve (GVV)  287 , conduit  273  may include a fill limit venting valve (FLVV)  285 , and conduit  275  may include a grade vent valve (GVV)  283 . Further, in some examples, recovery line  231  may be coupled to a fuel filler system  219 . In some examples, fuel filler system may include a fuel cap  205  for sealing off the fuel filler system from the atmosphere. Refueling system  219  is coupled to fuel tank  220  via a fuel filler pipe or neck  211 . 
     A canister internal filter  297  may in some examples be included in the canister  222 . Canister internal filter  297  may be positioned near purge line  228 , such that during purging of the canister to engine intake, dust particles from atmosphere and/or from the adsorbent material may be prevented from being routed through purge line  228 . For example, such dust particles may, over time, interact with canister purge valve  261 , which may result in purge valve  261  sticking closed, not fully opening, sticking open, etc. By including the canister internal filter  297 , such issues may be reduced or avoided. 
     An air intake system hydrocarbon trap (AIS HC)  294  may be placed in the intake manifold of engine  210  to adsorb fuel vapors emanating from unburned fuel in the intake manifold, puddled fuel from degraded injectors and/or fuel vapors in crankcase ventilation emissions during engine-off periods. The AIS HC may include a stack of consecutively layered polymeric sheets impregnated with HC (hydrocarbon) vapor adsorption/desorption material. Alternately, the adsorption/desorption material may be filled in the area between the layers of polymeric sheets. The adsorption/desorption material may include one or more of carbon, activated carbon, zeolites, or any other HC adsorbing/desorbing materials. When the engine is operational causing an intake manifold vacuum and a resulting airflow across the AIS HC, the trapped vapors are passively desorbed from the AIS HC and combusted in the engine. Thus, during engine operation, intake fuel vapors are stored and desorbed from AIS HC  294 . In addition, fuel vapors stored during an engine shutdown can also be desorbed from the AIS HC during engine operation. In this way, AIS HC  294  may be continually loaded and purged, and the trap may reduce evaporative emissions from the intake passage even when engine  210  is shut down. 
     Further, refueling system  219  may include refueling lock  245 . In some embodiments, refueling lock  245  may be a fuel cap locking mechanism. The fuel cap locking mechanism may be configured to automatically lock the fuel cap in a closed position so that the fuel cap cannot be opened. For example, the fuel cap  205  may remain locked via refueling lock  245  while pressure or vacuum in the fuel tank is greater than a threshold. In response to a refuel request, e.g., a vehicle operator initiated request, the fuel tank may be depressurized and the fuel cap unlocked after the pressure or vacuum in the fuel tank falls below a threshold. A fuel cap locking mechanism may be a latch or clutch, which, when engaged, prevents the removal of the fuel cap. The latch or clutch may be electrically locked, for example, by a solenoid, or may be mechanically locked, for example, by a pressure diaphragm. 
     In some embodiments, refueling lock  245  may be a filler pipe valve located at a mouth of fuel filler pipe  211 . In such embodiments, refueling lock  245  may not prevent the removal of fuel cap  205 . Rather, refueling lock  245  may prevent the insertion of a refueling pump into fuel filler pipe  211 . The filler pipe valve may be electrically locked, for example by a solenoid, or mechanically locked, for example by a pressure diaphragm. 
     In some embodiments, refueling lock  245  may be a refueling door lock, such as a latch or a clutch which locks a refueling door located in a body panel of the vehicle. The refueling door lock may be electrically locked, for example by a solenoid, or mechanically locked, for example by a pressure diaphragm. 
     In embodiments where refueling lock  245  is locked using an electrical mechanism, refueling lock  245  may be unlocked by commands from controller  212 , for example, when a fuel tank pressure decreases below a pressure threshold. In embodiments where refueling lock  245  is locked using a mechanical mechanism, refueling lock  245  may be unlocked via a pressure gradient, for example, when a fuel tank pressure decreases to atmospheric pressure. 
     Emissions control system  251  may include one or more emissions control devices, such as one or more fuel vapor canisters  222  filled with an appropriate adsorbent, the canisters configured to temporarily trap fuel vapors (including vaporized hydrocarbons) during fuel tank refilling operations and “running loss” (that is, fuel vaporized during vehicle operation). In one example, the adsorbent used is activated charcoal. Emissions control system  251  may further include a canister ventilation path or vent line  227  which may route gases out of the canister  222  to the atmosphere when storing, or trapping, fuel vapors from fuel system  218 . 
     Canister  222  may include a buffer  222   a  (or buffer region), each of the canister and the buffer comprising the adsorbent. As shown, the volume of buffer  222   a  may be smaller than (e.g., a fraction of) the volume of canister  222 . The adsorbent in the buffer  222   a  may be same as, or different from, the adsorbent in the canister (e.g., both may include charcoal). Buffer  222   a  may be positioned within canister  222  such that during canister loading, fuel tank vapors are first adsorbed within the buffer, and then when the buffer is saturated, further fuel tank vapors are adsorbed in the canister. In comparison, during canister purging, fuel vapors are first desorbed from the canister (e.g., to a threshold amount) before being desorbed from the buffer. In other words, loading and unloading of the buffer may not be linear with the loading and unloading of the canister. As such, the effect of the canister buffer is to dampen any fuel vapor spikes flowing from the fuel tank to the canister, thereby reducing the possibility of any fuel vapor spikes going to the engine. One or more temperature sensors  232  may be coupled to and/or within canister  222 . As fuel vapor is adsorbed by the adsorbent in the canister, heat is generated (heat of adsorption). Likewise, as fuel vapor is desorbed by the adsorbent in the canister, heat is consumed. In this way, the adsorption and desorption of fuel vapor by the canister may be monitored and estimated based on temperature changes within the canister. 
     Vent line  227  may also allow fresh air to be drawn into canister  222  when purging stored fuel vapors from fuel system  218  to engine intake  223  via purge line  228  and purge valve  261 . For example, purge valve  261  may be normally closed but may be opened during certain conditions so that vacuum from engine intake manifold  244  is provided to the fuel vapor canister for purging. In some examples, vent line  227  may include an air filter  259  disposed therein upstream of a canister  222 . In other examples, as will be discussed in further detail below, a purge pump  299  may be activated to draw atmospheric air across canister  222  and through open purge valve  261  to route fuel vapors desorbed from the canister to engine intake. Such action may be undertaken when intake manifold vacuum is not sufficient to be used for purging the canister, for example. 
     In some examples, the flow of air and vapors between canister  222  and the atmosphere may be regulated by a canister vent valve (not shown) coupled within vent line  227 . When included, the canister vent valve may be a normally open valve, so that fuel tank isolation valve  252  (FTIV) may control venting of fuel tank  220  with the atmosphere. FTIV  252  may be positioned between the fuel tank and the fuel vapor canister within conduit  278 . FTIV  252  may be a normally closed valve, that when opened, allows for the venting of fuel vapors from fuel tank  220  to canister  222 . However, in some examples the flow of air and vapors between canister  222  and atmosphere may be regulated by a changeover valve configured as part of an evaporative level check module (ELCM)  295 . Details of such an ELCM and associated changeover valve will be discussed in further detail below and particularly with regard to  FIGS. 3A-3E . 
     Fuel system  218  may be operated by controller  212  in a plurality of modes by selective adjustment of the various valves and solenoids. For example, the fuel system may be operated in a fuel vapor storage mode (e.g., during a fuel tank refueling operation and with the engine not running), wherein the controller  212  may open isolation valve  252  while closing canister purge valve (CPV)  261  to direct refueling vapors into canister  222  while preventing fuel vapors from being directed into the intake manifold. 
     As another example, the fuel system may be operated in a refueling mode (e.g., when fuel tank refueling is requested by a vehicle operator), wherein the controller  212  may open isolation valve  252 , while maintaining canister purge valve  261  closed, to depressurize the fuel tank before allowing enabling fuel to be added therein. As such, isolation valve  252  may be kept open during the refueling operation to allow refueling vapors to be stored in the canister. After refueling is completed, the isolation valve may be closed. As will be discussed in further detail below with regard to  FIGS. 15-17 , there may be circumstances where the canister purge valve may be commanded open during refueling, such that a fluid flow in the intake may be monitored, to indicate a presence or absence of evaporative emissions system degradation (e.g. canister internal filter restriction, CPV restriction, etc.). 
     As yet another example, the fuel system may be operated in a canister purging mode (e.g., after an emission control device light-off temperature has been attained and with the engine running), wherein the controller  212  may open canister purge valve  261  while closing isolation valve  252 . Herein, the vacuum generated by the intake manifold of the operating engine may be used to draw fresh air through vent  227  and through fuel vapor canister  222  to purge the stored fuel vapors into intake manifold  244 . In this mode, the purged fuel vapors from the canister are combusted in the engine. The purging may be continued until the stored fuel vapor amount in the canister is below a threshold. While the example above relies on intake manifold vacuum to conduct the purging operation, in other examples a canister purge pump  299  may be used, as discussed. In such an example, the controller  212  may open canister purge valve  261  with isolation valve  252  closed, and the purge pump may be activated to draw vacuum on the canister in order to draw atmospheric air across the canister to desorb fuel vapors and route the desorbed fuel vapors to engine intake. Similarly, such purging may be continued until stored fuel vapor amount in the canister is determined to be below a threshold. Discussed herein, activating purge pump  299  to draw vacuum on the canister may be understood to be activating purge pump  299  to operate in a forward direction, or via forward pump rotation. 
     In a vehicle system where the purge pump  299  is included, a purge pump bypass valve  299   c , a first bypass conduit  299   d  and second bypass conduit  299   e  may be included. First bypass conduit  299   d  may be fluidically coupled to purge line  228  downstream of purge pump  299 , and second bypass conduit  299   e  may be fluidically coupled to purge line  228  upstream of purge pump  299 . When the purge pump bypass valve  299   c  is open, it may be understood that fluid flow may be routed around purge pump  299 , via first bypass conduit  299   d  and second bypass conduit  299   e . Bypassing purge pump  299  may be useful when intake manifold vacuum is solely used for canister purging purposes, for example (e.g. purge pump off). Alternatively, when purge pump  299  is used for canister purging operations, purge pump bypass valve  299   c  may be commanded closed. Purge pump bypass valve  299   c  may be a solenoid valve, for example. In some examples, purge pump  299 , purge pump actuator  299   a , purge pump bypass valve  299   c , first bypass conduit  299   d , and second bypass conduit  299   e  may all be encompassed in one purge pump system  299   f.    
     In one example, it may be desirable to conduct a diagnostic as to whether canister purge valve  261  is functioning as desired (e.g. closing fully or sealing as desired), or in other words, is not degraded. Such a diagnostic may include applying intake manifold vacuum on the canister purge valve  261  while the canister purge valve is commanded fully closed. If a pressure change is indicated in the evaporative emissions system or fuel system (e.g. with isolation valve  252  also open), it may be determined that purge valve  261  is degraded as in the absence of degradation no change in pressure would be expected. In a case where purge pump  299  is included, such a diagnostic may further include commanding open purge pump bypass valve  299   c.    
     In another example, conducting a diagnostic as to whether canister purge valve  261  is degraded may include rotating canister purge pump  299  in a reverse direction, where vacuum is directed at the canister purge valve. Such a diagnostic may include commanding closed the canister purge valve  261 , commanding closed the purge pump bypass valve  299   c , and commanding closed the throttle  262 . The purge pump may then be activated in the reverse direction, and if a pressure change in the intake manifold  244  is indicated via, for example, MAP sensor  213 , then it may be determined that the canister purge valve  261  is degraded. Such a method may further include commanding/controlling closed intake valves of the engine. If, after a predetermined time period expires while vacuum is directed at the canister purge valve  261  without an indication of a pressure change in the intake, then purge pump bypass valve  299   c  may be commanded open to relieve the vacuum, and the purge pump  299  may be deactivated. It may be understood that operating the purge pump  299  in a forward-mode or reverse-mode may be via use of an H-bridge circuit to enable forward or reverse rotation of the purge pump  299 . 
     Controller  212  may comprise a portion of a control system  214 . It may be understood that control system  214  may be the same control system as control system  190  depicted above at  FIG. 1 . Control system  214  is shown receiving information from a plurality of sensors  216  (various examples of which are described herein) and sending control signals to a plurality of actuators  281  (various examples of which are described herein). As one example, sensors  216  may include exhaust gas sensor  237  located upstream of the emission control device, temperature sensor  233 , pressure sensor  291 , MAF sensor  202 , MAP sensor  213 , and canister temperature sensor  232 . Other sensors such as pressure, temperature, air/fuel ratio, and composition sensors may be coupled to various locations in the vehicle system  206 . As another example, the actuators may include fuel injector  266 , throttle  262 , fuel tank isolation valve  252 , purge pump actuator  299   a , and refueling lock  245 , purge pump bypass valve  299   c , etc. The control system  214  may include a controller  212 . The controller may receive input data from the various sensors, process the input data, and trigger the actuators in response to the processed input data based on instruction or code programmed therein corresponding to one or more routines. Example control routines are described herein with regard to  FIGS. 8-11, 15-16, and 18-19 . 
     In some examples, the controller may be placed in a reduced power mode or sleep mode, wherein the controller maintains essential functions only, and operates with a lower battery consumption than in a corresponding awake mode. For example, the controller may be placed in a sleep mode following a vehicle-off event in order to perform a diagnostic routine at a duration after the vehicle-off event. The controller may have a wake input that allows the controller to be returned to an awake mode based on an input received from one or more sensors, or in response to a predetermined duration of time elapsing, per a timer. As examples where sensors may trigger the awake mode, the opening of a vehicle door may trigger a return to an awake mode, or a remote start event may trigger a return to an awake mode. 
     Evaporative emissions test diagnostic routines may be intermittently performed by controller  212  on fuel system  218  and evaporative emissions control system  251  to confirm the presence or absence of undesired evaporative emissions. As such, evaporative emissions test diagnostic routines may be performed while the engine is off (engine-off test) using engine-off natural vacuum (EONV) generated due to a change in temperature and pressure at the fuel tank following engine shutdown and/or with vacuum supplemented from a vacuum pump (e.g.  295 ). Alternatively, evaporative emissions test diagnostic routines may be performed while the engine is running by using engine intake manifold vacuum. Evaporative emissions test diagnostics may be performed by an evaporative level check module (ELCM)  295  communicatively coupled to controller  212 . ELCM  295  may be coupled in vent  227 , between canister  222  and the atmosphere. ELCM  295  may include a vacuum pump for applying negative pressure to the fuel system when administering an evaporative emissions test. In some embodiments, the vacuum pump may be configured to be reversible. In other words, the vacuum pump may be configured to apply either a negative pressure or a positive pressure on the evaporative emissions system  251  and fuel system  218 . ELCM  295  may further include a reference orifice (e.g. 0.02″) and a pressure sensor  296 . A reference check may thus be performed whereby a vacuum may be drawn across the reference orifice, where the resulting vacuum level comprises a vacuum level indicative of an absence of undesired evaporative emissions. For example, following the reference check, the fuel system  218  and evaporative emissions system  251  may be evacuated by the ELCM vacuum pump. In the absence of undesired evaporative emissions, the vacuum may pull down to the reference check vacuum level. Alternatively, in the presence of undesired evaporative emissions, the vacuum may not pull down to the reference check vacuum level. 
     Turning to  FIGS. 3A-3D , they illustrate a schematic depiction of an example ELCM  295  in various conditions in accordance with the present disclosure. As shown in  FIG. 2 , ELCM  295  may be located along vent  227  between canister  222  and atmosphere. ELCM  295  includes a changeover valve (COV)  315 , a pump  330 , and pressure sensor  296 . Pump  330  may be a reversible pump, for example, a vane pump. COV  315  may be moveable between a first a second position. In the first position, as shown in  FIGS. 3A and 3C , air may flow through ELCM  295  via first flow path  320 . In the second position, as shown in  FIGS. 3B and 3D , air may flow through ELCM  295  via second flow path  325 . The position of COV  315  may be controlled by solenoid  310  via compression spring  305 . ELCM  295  may also comprise reference orifice  340 . Reference orifice  340  may have a diameter corresponding to the size of a threshold for undesired evaporative emissions to be tested, for example, 0.02″. In either the first or second position, pressure sensor  296  may generate a pressure signal reflecting the pressure within ELCM  295 . Operation of pump  330  and solenoid  310  may be controlled via signals received from controller  212 . 
     As will be discussed in further detail below, in addition to being utilized in order to conduct an evaporative emissions test diagnostic procedure, the ELCM pressure sensor and reference orifice may be relied upon to conduct an onboard flow test diagnostic procedure. Briefly, in one example various intake manifold vacuum(s) may be applied across the canister purge valve, at specified duty cycles of the canister purge valve (e.g. a first duty cycle rate and a second duty cycle rate for the CPV). For each manifold vacuum and duty cycle, a rate at which pressure is reduced to a predetermined vacuum (e.g. −20 InH2O) across reference orifice  340 , as monitored via the ELCM pressure sensor  296 , may be determined. Such a procedure may be conducted when it is known that the canister purge valve is functioning as desired, and thus may constitute baseline measurements. Then, at a later time or in response to an indication that the purge valve is not functioning as desired, that there is some level of canister internal filter clogging, etc., test measurements using the same methodology may be obtained and compared via the controller (e.g.  212 ) to the baseline measurements. A difference in values between test measurements and baseline measurements may enable determination of a canister purge valve degradation factor, which may then be used to update flow map(s) for the canister purge valve, to enable appropriate duty cycles for the purge valve to be selected via such flow map(s) for particular canister purging events. Compensating for evaporative emissions system degradation (e.g. canister purge valve degradation) may prevent engine hesitation and/or stall in response to purging events, may improve fuel economy, may increase engine lifetime, and may improve driveability and customer satisfaction. 
     As shown in  FIG. 3A , COV  315  is in the first position, and pump  330  is activated in a first direction. Air flow through ELCM  295  in this configuration is represented by arrows. In this configuration, pump  330  may draw a vacuum on reference orifice  340 , and pressure sensor  296  may record the vacuum level within ELCM  295 . This reference check vacuum level reading may then become the threshold for the presence or absence of undesired evaporative emissions in a subsequent evaporative emissions test diagnostic. 
     As shown in  FIG. 3B , COV  315  is in the second position, and pump  330  is activated in the first direction. This configuration allows pump  330  to draw a vacuum on fuel system  218  and evaporative emissions system  251 . In examples where fuel system  218  includes FTIV  252 , FTIV  252  may be opened to allow pump  330  to draw a vacuum on fuel tank  220 . Air flow through ELCM  295  in this configuration is represented by arrows. In this configuration, as pump  330  pulls a vacuum on evaporative emissions system  251  and fuel system  218 , the absence of undesired evaporative emissions in the systems should allow for the vacuum level in ELCM  295  to reach or exceed the previously determined reference vacuum threshold. In the presence of undesired evaporative emissions larger than the reference orifice, the pump may not pull down to the reference check vacuum level. 
     As shown in  FIG. 3C , COV  315  is in the first position, and pump  330  is de-activated. This configuration allows for air to freely flow between atmosphere and the canister. This configuration may be used during a canister purging operation, for example, and may additionally be used during vehicle operation when a purging operation is not being conducted, and when the vehicle is not in operation. In this way, changeover valve  315  may be used in lieu of a canister vent valve. 
     As shown in  FIG. 3D , COV  315  is in the second position, and pump  330  is activated in a second direction, opposite from the first direction. In this configuration, pump  330  may pull air from atmosphere into fuel system  218  and evaporative emission system  251 . In a configuration where FTIV  252  is open and CPV  261  is closed, air drawn by pump  330  may promote desorption of fuel vapor from canister  222 , and further direct the desorbed fuel vapor into fuel tank  220 . In this way, fuel vapor may be purged from the canister to the fuel tank, thereby decreasing the potential for bleed emissions. 
     Turning to  FIG. 3E , an example illustration of ELCM  295  is depicted illustrating how ELCM  295  may be used to conduct an onboard flow test diagnostic for the canister purge valve (e.g.  261 ). As discussed above, such a test may include establishing air flow across the canister purge valve via, for example, intake manifold vacuum, or via purge pump (e.g.  299 ) operating in the forward-mode of operation. Such air flow may be communicated to ELCM  295  as illustrated by arrows via duty cycling the canister purge valve. With the COV  315  configured in the second position, a vacuum may be drawn across reference orifice  340 , and with pump  296  off, vacuum may build in the evaporative emissions system. In other words, with the COV  315  configured in the second position, the evaporative emissions system may be sealed from communication with atmosphere along the vent line (e.g.  227 ). A rate at which vacuum develops in the evaporative emissions system as a function of canister purge valve duty cycle and either manifold vacuum level or purge pump speed may be used to determine a canister purge valve degradation factor. As discussed, such a canister purge valve degradation factor may be calculated based on baseline vacuum-build rates obtained when the canister purge valve is known to be free from degradation, as compared to test vacuum-build rates obtained when the canister purge valve is known to be degraded to at least some extent and/or periodically during the course of vehicle operation. Methods for determining such a canister purge valve degradation factor will be discussed in greater detail below with regard to the methods depicted at  FIGS. 8-11 . The canister purge valve degradation factor may be used to update a flow map (see for example  FIG. 6 ) that is used to control a duty cycle of the canister purge valve for purging the canister to engine intake, such that a commanded flow for a purging event may be accurately achieved, even under conditions where there is degradation of the canister purge valve, or in some cases other evaporative emissions system degradation (e.g. canister internal filter clogging, etc.). 
       FIG. 4  depicts an example embodiment of a combustion chamber or cylinder that may be included in engine  210  depicted in  FIG. 2 . Cylinder (i.e. combustion chamber)  230  may include combustion chamber walls  436  with piston  438  positioned therein. Piston  438  may include one or more piston rings  468 . The one or more piston rings  468  may function to seal cylinder  230 , to assist with piston heat transfer, and to regulate oil consumption, for example. Piston  438  may be coupled to crankshaft  474  so that reciprocating motion of the piston is translated into rotational motion of the crankshaft. Crankshaft  474  may be coupled to at least one drive wheel of the passenger vehicle via a transmission system. Further, a starter motor or electric machine may be coupled to crankshaft  474  via a flywheel to enable a starting operation of engine  210 , and/or to rotate the engine in an unfueled mode. 
     Cylinder  230  can receive intake air via intake air passage  244 , which may be one of a plurality of intake air passages coupled to cylinder  230 . Intake air passage  244  may communicate with other cylinders of engine  210  in addition to cylinder  230 . In some embodiments, one or more of the intake passages may include a boosting device such as a turbocharger or a supercharger. Exhaust passage  248  can receive exhaust gases from cylinder  230  as well as from other cylinders of engine  210 . 
     Each cylinder of engine  210  may include one or more intake valves and one or more exhaust valves. For example, cylinder  230  is shown including at least one intake poppet valve  456  and at least one exhaust poppet valve  450  located at an upper region of cylinder  230 . In some embodiments, each cylinder of engine  210 , including cylinder  230 , may include at least two intake poppet valves and at least two exhaust poppet valves located at an upper region of the cylinder. 
     Intake valve  456  may be controlled by a controller via actuator  452 . Similarly, exhaust valve  450  may be controlled by a controller via actuator  454 . During some conditions, the controller may vary the signals provided to actuators  452  and  454  to control the opening and closing of the respective intake and exhaust valves. The position of intake valve  456  and exhaust valve  450  may be determined by respective position sensors  499   a  and  499   b , respectively. The valve actuators may be of the electric valve actuation type or cam actuation type, or a combination thereof. The intake and exhaust valve timing may be controlled concurrently or any of a possibility of variable intake cam timing, variable exhaust cam timing, twin independent variable cam timing (TiVCT), or fixed cam timing may be used. Each cam actuation system may include one or more cams (e.g. actuator  452  and/or  454 ) and may utilize one or more of cam profile switching (CPS), variable cam timing (VCT), variable valve timing (VVT) and/or variable valve lift (VVL) systems that may be operated by a controller to vary valve operation. For example, cylinder  230  may alternatively include an intake valve controlled via electric valve actuation and an exhaust valve controlled via cam actuation including CPS and/or VCT. In other embodiments, the intake and exhaust valves may be controlled by a common valve actuator or actuation system, or a variable valve timing actuator or actuation system. 
     Shown for illustrative purposes at  FIG. 4  is an example of TiVCT. Specifically, an intake camshaft  481  and an exhaust camshaft  482  are illustrated. It may be understood that such a configuration may enable the ability to advance or retard timing of both the intake camshaft  481  and the exhaust camshaft  482  independently. Such an ability may allow for improved power and torque, particularly at lower engine speed (engine RPM), as well as improved fuel economy and reduced emissions. Such an ability may further enable precise control over intake and exhaust valve position, which may include in some examples positioning a particular cylinder with intake and exhaust valves both at least partially open. 
     In an example, a first oil pressure-controlled actuator  483  under control of the controller may regulate rotation of intake camshaft  481 , and a second oil pressure-controlled actuator  484  may regulate rotation of second camshaft  482 . In this way the first and second oil pressure-controlled actuators may control the camshafts to advance or retard engine timing based on operating conditions. For example, the controller may utilize crankshaft position sensor  497  and position sensor(s)  499   a  and  499   b  to determine engine timing. 
     While the example depicted herein at  FIG. 4  illustrates the actuators (e.g.  483  and  484 ) of the camshafts as oil pressure-controlled, there may be some examples where instead of oil pressure driven cam phasing, cam torque actuation (CTA) may be employed, which may utilize existing torsional energy in the valve train to rotate the camshaft(s), as is commonly understood in the art. 
     Cylinder  230  can have a compression ratio, which is the ratio of volumes within the cylinder between when piston  438  is at bottom dead center (BDC) and at top dead center (TDC). It may be understood that, as discussed herein, BDC may comprise a position of piston  438  being in closest proximity to crankshaft  474 , whereas TDC may comprise a position of piston  438  being at a position farthest from crankshaft  474 . Furthermore, it may be understood that, as discussed herein, TDC may be understood to be 180° from BDC. Conventionally, the compression ratio is in the range of 9:1 to 10:1. However, in some examples where different fuels are used, the compression ratio may be increased. This may happen for example when higher octane fuels or fuels with higher latent enthalpy of vaporization are used. The compression ratio may also be increased if direct injection is used due to its effect on engine knock. 
     In some embodiments, each cylinder of engine  210  may include a spark plug  492  for initiating combustion. An ignition system (not shown) can provide an ignition spark to cylinder  230  via spark plug  492  in response to a spark advance signal from a controller, under select operating modes. However, in some embodiments, spark plug  492  may be omitted, such as where engine  210  may initiate combustion by auto-ignition or by injection of fuel as may be the case with some diesel engines. 
     In some embodiments, each cylinder of engine  210  may be configured with one or more fuel injectors for providing fuel thereto. As a non-limiting example, cylinder  230  may include two fuel injectors (e.g., a port fuel injector and a direct fuel injector). Fuel injector  266  is shown coupled directly to cylinder  230  for injecting fuel directly therein in proportion to a pulse width of a signal received from a controller via an electronic driver. In this manner, fuel injector  266  provides what is known as direct injection (hereafter referred to as “DI”) of fuel into cylinder  230 . While  FIG. 4  shows injector  266  as a side injector, it may also be located overhead of the piston, such as near the position of spark plug  492 . Such a position may improve mixing and combustion when operating the engine with an alcohol-based fuel due to the lower volatility of some alcohol-based fuels. Alternatively, the injector may be located overhead and near the intake valve to improve mixing. Fuel may be delivered to fuel injector  266  from a high pressure fuel system including a fuel tank, fuel pumps, a fuel rail, etc. Alternatively, fuel may be delivered by a single stage fuel pump at lower pressure, in which case the timing of the direct fuel injection may be more limited during the compression stroke than if a high pressure fuel system is used. 
     Fuel may be delivered to the cylinder during a single cycle of the cylinder. Discussed herein, a single engine cycle includes an exhaust stroke, an intake stroke, a compression stroke, and a power stroke. It may be further understood that, when a piston is within a threshold (e.g. within 5°) of TDC between the exhaust stroke and the intake stroke, both the intake valve and the exhaust valve may be at least partially open. Directly injected fuel may be delivered during an intake stroke as well as partly during a previous exhaust stroke. Further, the direct injected fuel may be delivered as a single injection or as multiple injections. These may include multiple injections during the compression stroke, multiple injections during the intake stroke or a combination of some direct injections during the compression stroke and some during the intake stroke. When multiple direct injections are performed, the relative distribution of the total directed injected fuel between an intake stroke (direct) injection and a compression stroke (direct) injection may be referred to as a second injection ratio. For example, injecting a larger amount of the direct injected fuel for a combustion event during an intake stroke may be an example of a higher second ratio of intake stroke direct injection, while injecting a larger amount of the fuel for a combustion event during a compression stroke may be an example of a lower second ratio of intake stroke direct injection. Note that these are merely examples of different injection ratios, and various other injection ratios may be used. 
     A positive crackcase ventilation (PCV) system, may be coupled to the engine intake so that gasses in the crankcase  462  may be vented in a controlled manner from the crankcase. Engine  210  may include a crankcase ventilation tube  458 , and a PCV line  460  in order to vent gasses out of the crankcase  462  and into intake manifold. In some examples PCV line  460  may include PCV valve  464 , which may be an electronically controlled valve (e.g., a powertrain control module (PCM) controlled valve) wherein a controller may command a signal to change a position of the valve from an open position (or a position of high flow) to a closed position (or a position of low flow), or vice versa, or any position there-between. 
     As described above,  FIG. 4  shows only one cylinder of a multi-cylinder engine. As such each cylinder may similarly include its own set of intake/exhaust valves, fuel injector(s), spark plugs, piston rings, etc. 
     Thus, a system for a hybrid vehicle comprises a fuel vapor storage canister positioned in an evaporative emissions system; a canister purge valve positioned in a purge line fluidically coupling the fuel vapor storage canister to an intake of an engine; a pump positioned in a vent line that couples the fuel vapor storage canister to atmosphere, the pump including a changeover valve configurable to a first position and a second position where the vent line is sealed from atmosphere when the changeover valve is configured in the second position, the pump further including a reference orifice and a pressure sensor configured to measure a pressure difference across the reference orifice; and a vacuum source downstream of the fuel vapor storage canister for applying a predetermined negative pressure on the evaporative emissions system. In such a system, the system may further comprise a controller with computer readable instructions stored on non-transitory memory that when executed, cause the controller to obtain a first baseline rate and a second baseline rate at which pressure in the evaporative emissions system is reduced to a predetermined vacuum level by configuring the changeover valve in the second position to seal the evaporative emissions system and applying the predetermined negative pressure on the evaporative emissions system via the vacuum source while the canister purge valve is duty cycled at a first rate and then a second rate; at a later time, obtain a first test rate and a second test rate at which pressure in the evaporative emissions system is reduced to the predetermined vacuum level by configuring the changeover valve in the second position and applying the negative pressure on the evaporative emissions system via the vacuum source while the canister purge valve is duty cycled at the first rate and then the second rate; compare the first and second test rates with the first and second baseline rates to obtain a degradation factor that is used to update a flow map stored at the controller that is used to control the canister purge valve for purging fuel vapors from the fuel vapor storage canister; and in response to a request to purge the canister, controller the canister purge valve based on the updated flow map. 
     Such a system may further comprise a motor configured to rotate the engine unfueled, and \wherein the controller stores further instructions to rotate the engine unfueled to provide the vacuum source for applying the predetermined negative pressure on the evaporative emissions system. 
     Such a system may further comprise a purge pump positioned between the canister purge valve and the fuel vapor storage canister, and where the controller stores further instructions to operate the purge pump to provide the vacuum source for applying the predetermined negative pressure on the evaporative emissions system. 
     In another example, a system for a hybrid vehicle comprises a fuel vapor storage canister positioned in an evaporative emissions system of the hybrid vehicle, the fuel vapor storage canister selectively fluidically coupled to a fuel system via a fuel tank isolation valve and selectively fluidically coupled to an intake of an engine via a canister purge valve; a throttle positioned in the intake of the engine; a plurality of intake valves configured to regulate air flow to the engine; and a mass air flow sensor positioned in the intake of the engine. In such a system, the system may further comprise a controller with computer readable instructions stored on non-transitory memory that when executed, cause the controller to: with the engine not combusting air and fuel, in a first condition, operate the evaporative emissions system in a first mode to direct a first test flow that is negative with respect to atmospheric pressure to the intake and indicate evaporative emissions system degradation in response to the first test flow being outside of a first predetermined threshold of a first baseline flow obtained via operating the evaporative emissions system in the first mode, where the first test flow and first baseline flow are indicated via the mass air flow sensor; and in a second condition, operate the evaporative emissions system in a second mode to direct a second test flow that is positive with respect to atmospheric pressure to the intake and indicate evaporative emissions system degradation in response to the second test flow being outside of a second predetermined threshold of a second baseline flow obtained via operating the evaporative emissions system in the second mode, where the second test flow and the second baseline flow are monitored via the mass air flow sensor. 
     In such a system, the system may further comprise a pump positioned in the evaporative emissions system between the fuel vapor storage canister and atmosphere. In such a system, the controller may store further instructions to, in the first condition, command fully open the canister purge valve, command fully closed the fuel tank isolation valve, command fully open the throttle, control the engine to substantially close the plurality of intake valves, and operate the pump at a predetermined speed to direct the first test flow to the intake, where the predetermined speed comprises a same speed as that utilized for obtaining the first baseline flow. 
     In such a system, the controller may store further instructions to, in the second condition, in response to a request for refueling of a fuel tank positioned in the fuel system, command fully open the fuel tank isolation valve to enable refueling of the fuel tank, and in response to an absence of premature shutoffs of a refueling dispenser during the refueling, and in response to an indication that a fuel fill rate comprises a predetermined fuel fill rate, direct the second test flow to the intake via commanding fully open the canister purge valve with the fuel tank isolation valve open, commanding fully open the throttle, and controlling the engine to substantially close the plurality of intake valves. 
     Turning now to  FIGS. 5A-5D , they show examples of canister purge valve (CPV) flow obtained in an offboard fashion, for example via a technician at a bench using a flow meter to measure flow rate, or standard liter per minute across a CPV at particular levels of intake vacuum ( FIG. 5A ,  FIG. 5C ), or at particular purge pump speeds ( FIG. 5B ,  FIG. 5D ). As discussed above, such flow may be used to establish flow maps that are stored at a controller (e.g.  212 ), such that when a particular flow is requested via onboard strategy for a particular canister purging event, an appropriate duty cycle may be determined. 
     At  FIG. 5A , depicted is a graph  500  of three examples of intake manifold vacuum. A first, greatest manifold vacuum  502 , a second, medium manifold vacuum  504 , and a third, lowest manifold vacuum  506 , are shown. As illustrated, flow across the CPV increases as duty cycle increases and as intake manifold vacuum increases. 
       FIG. 5B , alternatively, depicts a graph  525  of a similar example, but where three levels of purge pump speeds are utilized rather than intake manifold vacuum. Depicted is a first, greatest pump speed  522 , a second, medium pump speed  524 , and a third, lowest pump speed  526 . Flow across the CPV increases as duty cycle increases and as purge pump speed increases. 
     While only three examples of manifold vacuum ( FIG. 5A ), and only three examples of purge pump speed ( FIG. 5B ) are shown, it may be understood that more than three manifold vacuums may be utilized, and more than three purge pump speeds may be utilized, for the generation of CPV flow map(s) to be stored at the controller. 
     Turning now to  FIG. 5C , graph  550  shows an example of flow obtained across the same CPV as that depicted at  FIG. 5A , the flow obtained under similar conditions (e.g. via a technician in an offboard fashion using a flow meter), after the CPV has been used in the vehicle for some time. In other words,  FIG. 5C  depicts how flow across such a CPV may vary due to degradation of the valve (or in some cases canister internal filter restriction, a source of undesired evaporative emissions, etc.), over time. Line  502   a  represents flow obtained at the same manifold vacuum as line  502 , illustrating less overall flow as a function of duty cycle of the CPV. Similarly, line  504   a  represents flow obtained at the same manifold vacuum as line  504 , and line  506   a  represents flow obtained at the same manifold vacuum as line  506 , where each have less overall flow as a function of duty cycle of the CPV. Thus, in this example, the degradation may include the CPV not fully opening, or sticking upon closure, thus resulting in less overall flow as compared to the baseline measurements (e.g. line  502 ,  504 ,  506 ), for example. Depending on the level to which flow is affected, a determination may be made as to how flow is affected (e.g. to what extent the CPV is degraded), and how to compensation for such degradation. While this example depicts a situation where less flow is observed, it is also possible that greater flow may be seen in such a test, for example if the CPV does not properly close or if the CPV sticks open to some extent while duty cycling the CPV. 
     Turning now to  FIG. 5D , graph  575  shows an example of flow obtained across the same CPV as that depicted at  FIG. 5B , the flow obtained under similar conditions (e.g. via a technician in an offboard fashion using a flow meter), after the CPV has been used in the vehicle for some time. Line  522   a  represents flow obtained at the same purge pump speed as line  522 , line  524   a  represents flow obtained at the same purge pump speed as line  524 , and line  526   a  represents flow obtained at the same purge pump speed as line  526 . In this example, each depict greater overall flow as a function of CPV duty cycle. Thus, in this example, the degradation may include the CPV not fully closing or sticking open during the duty cycling of the valve. Similarly as that discussed above at  FIG. 5C , depending on a level to which flow is affected, a determination can be made as to how flow is affected (e.g. to what extent the CPV is degraded, for example), and in some examples, may enable a determination as to how to compensate for such degradation. For example, a flow map may be updated to account for the type of degradation observed experimentally via a technician, provided the valve is still used in the vehicle after the conducting of such a diagnostic. 
     Turning to  FIG. 6 , an example of a CPV flow map  600  as discussed herein, is shown. Briefly, flow map  600  is a function of intake manifold vacuum (calculated as manifold vacuum minus fuel tank pressure, corrected for barometric pressure) versus flow (standard liter per minute). As discussed above, such a flow map may be generated via a technician at a bench, prior to the CPV being utilized in a vehicle. When the vehicle is in operation, such a flow map may be utilized to control a duty cycle of the CPV depending on a flow rate requested via the controller. For example (see dashed oval), when a flow of 0.03 lb/minute is requested or commanded via the controller, and differential pressure across the CPV is 0.590 atm, flow map  600  may be queried where it may be determined that CPV duty cycle may be commanded to 14.8% in order to achieve the commanded flow. 
     While  FIG. 6  depicts an example of a CPV flow map consisting of commanded flow as a function of intake manifold vacuum calculated as discussed above, to arrive at a duty cycle to achieve the commanded flow, in another example such a flow map may be a function of purge pump speed, or pressure difference across a CPV as a function of purge pump speed. In such an example, such a CPV flow map may similarly be used to determine a duty cycle for a commanded flow as a function of purge pump speed and/or pressure difference across the CPV as a function of purge pump speed. 
     As discussed, such flow maps may be useful for controlling/regulating an amount of vapors introduced into an engine while the engine is operating to combust air and fuel during a purge event. However, there may be circumstances where the purge valve becomes degraded to some extent (or in some cases a canister internal filter becomes restricted, etc.), and thus such flow maps may no longer be representative. In such an example, commanding a particular duty cycle to achieve a requested or commanded flow may, in fact, result in more or less actual flow. Such discrepancy may result in driveability issues, engine hesitation or stall, etc. Thus, it may be desirable to be able to periodically update such flow maps as that depicted at  FIG. 6 , via an onboard method that does not involve having the vehicle serviced via a technician. 
     Methods discussed herein and with regard to  FIGS. 8-11  may enable onboard determination of CPV flow, such that flow map(s) such as that depicted at  FIG. 6  may be updated to provide a more accurate flow map reflective of a current state of the CPV being utilized in a particular vehicle. While such methods will be discussed in detail below,  FIGS. 7A-7B  graphically depict such methods and will be briefly described prior to turning to  FIGS. 8-11 . 
       FIG. 7A  graphically depicts an example methodology  700  for determining CPV flow in an onboard fashion, for example while the vehicle is in operation. The method includes, at different levels of intake manifold vacuum, establishing sets of baseline rates at which a predetermined vacuum level is established in a vehicle evaporative emissions system, as a function of duty cycle of the CPV, and then at a later time, establishing test rates at different level of intake manifold vacuum at which the same predetermined vacuum level is established in the evaporative emissions system as a function of CPV duty cycle. Only two duty cycles may be utilized for both the baseline and test diagnostics in some examples, however in other examples more than two duty cycles may be used. In the case of two or more duty cycles used, a straight line may be drawn between a rate at which the particular vacuum is reached for one duty cycle, and the rate at which the particular vacuum is reached for other duty cycles. As discussed, an ELCM (e.g.  295 ) may be used including a reference orifice (e.g.  340 ) and pressure sensor (e.g.  296 ), and a changeover valve (e.g.  315 ), where the changeover valve is configured in a second position for conducting the baseline and test diagnostics to seal the evaporative emissions system from atmosphere. 
     Accordingly, line  702  represents such a line established between a rate at which the predetermined vacuum is reached for a first duty cycle, and a second duty cycle, for a first vacuum level. Lines  704 ,  706 ,  708 , and  710  similarly represent such lines obtained for second, third, fourth, and fifth vacuum levels, respectively. In this example it may be understood that line  702  represents the lowest level of intake manifold vacuum, while line  710  represents the greatest level of intake manifold vacuum. It may be understood that lines  702 ,  704 ,  706 ,  708 , and  710  are obtained when the CPV is known to not be degraded to any significant extent, thus constituting the baseline rates at which the predetermined vacuum level is reached. 
     At a later time, when the CPV (or in some cases other components of the evaporative emissions system such as the canister internal filter being clogged) is known to be degraded or after a predetermined time elapses where a request to conduct such a test is commanded via the controller, test measurements represented by lines  702   a ,  704   a ,  706   a ,  708   a , and  710   a  may be obtained. It may be understood that in this example, line  702   a  corresponds to the same (e.g. within a predetermined threshold such as within 1% difference or less) intake manifold vacuum level as that for which line  702  was established, line  704   a  corresponds to the vacuum for which line  704  was established, line  706   a  corresponds to the vacuum for which line  706  was established, line  708   a  corresponds to the vacuum for which line  708  was established, and line  710   a  corresponds to the vacuum for which line  710  was established. In this example, for all cases the rate for which vacuum in the evaporative emissions system reached the predetermined vacuum level increased (in other words, took less time for the predetermined vacuum level to be reached). Thus, in this example, it may be understood that the CPV may not be closing fully or may be staying open longer than desired to enable a more rapid rate at which pressure in the evaporative emissions system is reduced to the predetermined vacuum level for the various levels of intake manifold vacuum. 
     With such a pattern of data established, a CPV degradation factor may be determined via the controller for each level of manifold vacuum. Such degradation factors may comprise a difference between baseline data (e.g.  702 ) and test data (e.g.  704 ). Accordingly, various determination of degradation factors  703 ,  705 ,  707 ,  709 , and  711  are depicted. In some examples, such degradation factors may be averaged or otherwise processed via the controller to obtain a high-confidence degradation factor. Such degradation factor(s) may then be used to update the CPV flow map stored at the controller, such as the CPV flow map depicted at  FIG. 6 . Updating the CPV flow map may include accounting for the degradation such that, when a particular flow value is commanded via the controller for a purge event, the CPV is controlled such that that an actual flow equal to the particular commanded flow is achieved, whereas if the flow map had not been updated, the actual flow value may not correspond to the particular commanded flow value. 
       FIG. 7B  depicts a similar example graph  750  as that depicted at  FIG. 7A , however rather than intake manifold vacuum, purge pump speed is the variable. More specifically, baseline data (lines  752 ,  754 ,  756 ,  758 ,  760 ) may be obtained for at least two different duty cycles of the CPV for various speeds of the purge pump, and then test data (lines  752   a ,  754   a ,  756   a ,  758   a ,  760   a ) may be obtained at the same duty cycles and corresponding pump speeds. Again, baseline and test data comprise a rate at which a predetermined threshold vacuum is reached in the evaporative emission system as monitored via the ELCM pressure sensor, at particular duty cycles, for particular pump speeds. For clarity pump speed for obtaining line  752  comprises the same pump speed as that for obtaining line  752   a , line  754  comprises the same pump speed as that for obtaining line  754   a , line  756  comprises the same pump speed as that for obtaining line  756   a , line  758  comprises the same pump speed as that for obtaining line  758   a , and line  760  comprises the same pump speed as that for obtaining line  760   a . Furthermore, it may be understood that in this example, line  752  (and  752   a ) was obtained with the lowest pump speed while line  760  (and  760   a ) was obtained with the greatest pump speed. 
     In the example depicted at  FIG. 7B , for all pump speeds tested, the rate at which the predetermined threshold vacuum was reached is decreased for the test measurements ( 752   a ,  754   a ,  756   a ,  758   a ,  760   a ) as compared to the baseline measurements ( 752 ,  754 ,  756 ,  758 ,  760 ). In other words, for each pump speed, it is taking longer for the pressure in the evaporative emissions system to be reduced to the predetermined threshold vacuum, for each duty cycle tested for the test data as compared to the baseline data. Thus, in this example, it may be understood that the CPV may be sticking closed, or not fully opening, thus resulting in a decreased rate at which pressure in the evaporative emissions system is reduced to the predetermined vacuum level for the various pump speeds tested. 
     Similar to that discussed above for  FIG. 7A , with such a pattern of data established, a CPV degradation factor may be determined via the controller for each purge pump speed. Such degradation factors may comprise a difference between baseline data (e.g.  752 ) and test data (e.g.  752   a ). Accordingly, various determination of degradation factors  753 ,  755 ,  757 ,  759 , and  761  are depicted. Averaging or otherwise processing the degradation factor data may be conducted via the controller to obtain a high-confidence degradation factor. Such degradation factor(s) may then be used to update the CPV flow map stored at the controller, such a flow map corresponding to a flow map that relies on the purge pump for purging operations. 
     In a case where such baseline and test data are obtained using intake manifold vacuum, either the engine may be combusting air and fuel, or the engine may be rotated unfueled via, for example, a motor (e.g.  120 ), to generate the manifold vacuum. If the engine is rotated unfueled to generate the intake manifold vacuum for the baseline and test data, then a pre-condition may include a canister that is clean (e.g. loaded to less than a threshold amount, for example less than 5%, less than 1%, etc.), so as not to introduce fuel vapors to the engine. 
     Furthermore, in a case where baseline and test data are obtained using intake manifold vacuum, if a purge pump is included in the purge line, then it may be understood that a purge pump bypass valve (e.g.  299   c ) may be commanded open (in addition to duty cycling the CPV) to enable communication of the intake manifold vacuum with the ELCM. 
     In a case where baseline and test data are obtained using the purge pump to establish air flow across the CPV, an intake throttle (e.g.  262 ) may be commanded fully open, or may be controlled to a predetermined position. 
     Furthermore, while various methods (e.g. engine on and combusting, unfueled engine rotation, use of purge pump) are discussed herein for how to establish rates (baseline and test rates) at which vacuum in the evaporative emissions system is reduced to the predetermined threshold vacuum level it may be understood that degradation factors used to update CPV flow maps may be confined to the flow maps corresponding to the way in which the degradation factors were determined. For example, degradation factors determined via methodology comprising use of the purge pump (see for example  FIG. 7B ) may be used to update a CPV flow map that corresponds to use of the purge pump for canister purging. Alternatively, degradation factors determined via methodology comprising use of intake manifold vacuum (see for example  FIG. 7A ) may be used to update a CPV flow map that corresponds to use of intake manifold vacuum for canister purging. 
     Still further, it may be understood that the general methodology depicted at  FIGS. 7A-7B  relies on the duty cycle itself not influencing the degradation the methodology is attempting to address. For example, if the valve is sticking at low duty cycle rates, but not at higher duty cycle rates, then the lines drawn between duty cycles for the above-mentioned conditions may not be linear and in such examples it may be difficult to ascertain degradation factors based on the above-described methodology. Thus, enablement for the methodology to obtain degradation factors may include an indication that both the baseline measurements and test measurements are linear, with a similar slope for both the baseline measurements and test measurements as a function of duty cycle. 
     Turning now to  FIG. 8 , a high-level flowchart for an example method  800  for obtaining measurements of CPV flow in an onboard fashion without having to service a vehicle, is shown. Such a method may be used to obtain one or more high-confidence degradation factor(s) which may be utilized to update one or more CPV flow map(s) stored at a controller of the vehicle. In this way, in response to an aged or degraded CPV (or in some cases other evaporative emissions system degradation such as a canister internal filter that may be clogged or plugged to at least some extent) where a particular CPV flow map is no longer representative of the flow characteristics through the CPV, the flow map may be updated such that a commanded flow may be accurately produced via a duty cycle obtained via the updated flow map for purging the canister. 
     Method  800  will be described with reference to the systems described herein and shown in  FIGS. 1-4 , though it will be appreciated that similar methods may be applied to other systems without departing from the scope of this disclosure. Instructions for carrying out method  800  and the rest of the methods included herein may be executed by a controller, such as controller  212  of  FIG. 2 , based on instructions stored in non-transitory memory, and in conjunction with signals received from sensors of the engine system, such as temperature sensors, pressure sensors, and other sensors described in  FIGS. 1-4 . The controller may employ actuators such as motor (e.g.  120 ), purge pump actuator (e.g.  299   a ) for controlling the purge pump (e.g.  299 ), throttle (e.g.  262 ), CPV (e.g.  261 ), ELCM COV (e.g.  315 ), etc., according to the methods described herein. 
     Method  800  begins at  805  and may include obtaining onboard baseline CPV flow data responsive to conditions being met for doing so. Conditions being met may include a CPV that is new, or in use for less than a predetermined threshold amount of time (e.g. 1 day, 2 days, etc.). Conditions being met may further include an indication of no degradation in the vehicle evaporative emissions system, no indication of CPV degradation, no indication of ELCM degradation, no indication of FTIV degradation, no indication of purge pump bypass valve degradation (where included), no indication of canister internal filter restriction/clogging, an air filter that is not restricted, etc. 
     As discussed above with regard to  FIGS. 7A-7B  obtaining baseline data may include establishing rates at which a predetermined threshold vacuum level (e.g. −20 InH2O) is reached across a reference orifice (e.g.  340 ) in an evaporative emissions system as monitored via an ELCM pressure sensor (e.g.  296 ), at different levels of either intake manifold vacuum or purge pump speed, for at least two different duty cycles of the CPV for each level of manifold vacuum or each purge pump speed. With such rates established, a straight line may be drawn between the rates obtained for the different duty cycles for each particular intake manifold vacuum level, or between the rates obtained for the different duty cycles for each particular purge pump speed. Proceeding to  810 , method  800  may include storing such data at the controller of the vehicle. 
     With the baseline data obtained, method  800  may proceed to  815 . At  815 , method  800  may include obtaining onboard test CPV flow data responsive to conditions being met for doing so. Conditions being met may include an indication of CPV degradation (and/or in some examples other evaporative emissions system degradation such as a clogged canister internal filter), an indication that a predetermined time period has elapsed since the baseline measurements were obtained, and/or a predetermined time since other test measurements were obtained. Conditions being met at  815  may further include no indication of ELCM degradation, no indication of FTIV degradation, etc. In some examples, conditions being met at  815  may include an indication of no sources of undesired evaporative emissions stemming from the evaporative emissions system, however in other examples conditions being met at  815  may include an indication of a source of undesired evaporative emissions stemming from the evaporative emissions system, without departing from the scope of this disclosure. At  815 , the test measurements may be obtained in the same fashion as the baseline measurements, discussed above with regard to  FIGS. 7A-7B , the data from which may be stored at the controller at step  820 . 
     With such baseline and test measurements obtained, method  800  may proceed to  825 . At  825 , method  800  may include determining a CPV degradation factor based on a difference between the baseline measurements and test measurements for each manifold vacuum, or purge pump speed. In some examples, the CPV degradation factor obtained for each manifold vacuum condition may be averaged or otherwise processed to obtain a high-confidence CPV degradation factor. Similarly, in some examples, the CPV degradation factor obtained for each purge pump speed condition may be averaged or otherwise processed to obtain a high-confidence CPV degradation factor. With such CPV degradation factors obtained, method  800  may proceed to  830 . At  830 , method  800  may include adjusting or updating corresponding CPV flow maps as a function of the corresponding CPV degradation factor. For example, one CPV flow map may correspond to a flow map if engine intake manifold vacuum is used for purging, while another CPV flow map may correspond to a flow map if the purge pump is used for purging. Thus, degradation factors obtained via the use of intake manifold vacuum may be used to update a CPV flow map that relies upon intake manifold vacuum for purging operations, while degradation factors obtained via the use of the purge pump may be used to update a CPV flow map that relies upon the purge pump for purging operations. Such updated flow maps may be stored at the controller of the vehicle. 
     Proceeding to  835 , method  800  may include controlling future purging events according to the updated CPV flow maps to account for CPV degradation. In other words, if a purging event is requested that relies on intake manifold vacuum, then the updated CPV flow map that is based on intake manifold vacuum for determining CPV duty cycle, may be relied upon for conducting the canister purging operation. Alternatively, if a purging event is requested that relies on the purge pump, then the updated CPV flow map that is based on the use of the purge pump for determining CPV duty cycle may be relied upon for conducting the canister purging operation. 
     In this way, the CPV flow maps may be continually updated to account for CPV degradation over time. By accounting for varying levels of CPV degradation, and updating CPV flow maps accordingly, a requested purge flow may be accurately established via a duty cycle of the CPV as determined according to the updated CPV flow maps. 
     As discussed above, there may be several ways in which to obtain the onboard baseline and test CPV flow data. Accordingly, such methodologies will be discussed in more detail below with regard to  FIGS. 9-11 . 
     Turning to  FIG. 9 , a high-level flowchart for an example method  900  for obtaining baseline or test CPV flow data using intake manifold vacuum under conditions where an engine of the vehicle is combusting air and fuel, is shown. More specifically, as discussed with regard to method  800 , to acquire degradation factors based on onboard CPV flow mapping, both baseline and test measurements may be acquired. It may be understood that the same methodology for obtaining the baseline measurements may be used for obtaining test measurements. Accordingly, only one method is illustrated but it may be understood that method  900  may be used to obtain either baseline or test measurements. 
     Method  900  will be described with reference to the systems described herein and shown in  FIGS. 1-4 , though it will be appreciated that similar methods may be applied to other systems without departing from the scope of this disclosure. Instructions for carrying out method  900  and the rest of the methods included herein may be executed by a controller, such as controller  212  of  FIG. 2 , based on instructions stored in non-transitory memory, and in conjunction with signals received from sensors of the engine system, such as temperature sensors, pressure sensors, and other sensors described in  FIGS. 1-4 . The controller may employ actuators such as motor (e.g.  120 ), purge pump bypass valve (e.g.  299   c ), throttle (e.g.  262 ), CPV (e.g.  261 ), ELCM COV (e.g.  315 ), etc., according to the methods described herein. 
     Method  900  begins at  905  and may include indicating whether the engine is combusting air and fuel. If not, method  900  may proceed to method  1000  depicted at  FIG. 10 . If, at  905 , it is indicated that the engine is combusting air and fuel, method  900  may proceed to  915 . At  915 , method  900  may include indicating whether conditions are met for obtaining baseline or test CPV flow data. For example, as discussed, conditions being met for specifically obtaining baseline CPV flow data may include an indication that the CPV is within a threshold amount of time from being installed in the vehicle (e.g. less than 1 day, less than 2 days, etc.), or in other words, no indication of CPV degradation. Conditions being met for specifically obtaining baseline CPV flow data may additionally include an indication of an absence of undesired evaporative emissions or other degradation in the evaporative emissions system. Conditions being met for specifically obtaining test CPV flow data may include an indication that a threshold duration of time has elapsed since baseline measurements were obtained, or a threshold duration of time since prior test measurements were obtained, an indication of CPV degradation to some extent, etc. Conditions being met for obtaining test CPV flow data may include an indication of no sources of undesired evaporative emissions in the vehicle evaporative emissions system (or in some examples an indication of a source of undesired evaporative emissions), no indication of ELCM degradation, no indication of FTIV degradation, etc. 
     Furthermore, at  915 , conditions being met may include an indication of a stable intake manifold vacuum. For example, such instances may occur while the vehicle is in operation and changes in torque are not being requested by the vehicle operator. In some examples where the engine is equipped with variable cam timing capabilities (e.g. Ti-VCT), then actuators (e.g.  483 ,  484 ) may be controlled such that engine intake manifold vacuum is maintained while the baseline or test measurements are being obtained as per method  900 . Additionally or alternatively, for a hybrid vehicle such as that depicted at  FIG. 1 , a motor (e.g.  120 ) may be used to maintain requested torque while controlling the engine to ensure constant intake manifold vacuum during the acquiring of baseline or test measurements. Still further, the throttle (e.g.  262 ) may be controlled during the acquiring of the baseline or test measurements to maintain constant intake manifold vacuum. In other words, when using intake manifold vacuum while the engine is combusting air and fuel to obtain the baseline or test CPV flow measurements, a constant (e.g. variation less than a predetermined threshold, such as less than 1% variation or less than 5% variation) intake manifold vacuum may be maintained. An indication of vacuum level in the intake manifold may be provided via a MAP sensor (e.g.  213 ), and may be referenced to pressure in the evaporative emissions system via the ELCM pressure sensor (e.g.  296 ), and may in some examples further be compensated as a function of barometric pressure. 
     If, at  915 , conditions are not met for obtaining baseline or test data, method  900  may proceed to  920 . At  920 , method  900  may include maintaining current vehicle operating conditions. In other words, engine operation may be maintained in its current state of operation and method  900  may end. 
     Returning to  915 , responsive to conditions being met for obtaining the baseline or test data, method  900  may proceed to  925 . At  925 , method  900  may include configuring the ELCM COV (e.g.  315 ) in the second position (refer to  FIG. 3E ), to seal the evaporative emissions system from atmosphere. Furthermore, while not explicitly illustrated, for vehicles equipped with a purge pump (e.g.  299 ) and purge pump bypass valve (e.g.  299   c ), the purge pump bypass valve may be commanded fully open. Still further, the FTIV (e.g.  252 ) may be commanded or maintained closed. 
     Proceeding to  930 , method  900  may include duty cycling the CPV (e.g.  261 ) at a first rate (e.g. 90%). With the CPV being duty cycled at the first rate, method  900  may proceed to  935  and may include measuring pressure decrease, or vacuum-build, in the evaporative emissions system via the ELCM pressure sensor. Proceeding to  940 , method  900  may include recording a rate at which pressure in the evaporative emissions system is reduced to a predetermined threshold vacuum (e.g. −20InH2O). The results may be stored at the controller at step  945 . 
     With the predetermined vacuum-build reached and the rate at which the predetermine vacuum-build was reached stored at the controller, method  900  may proceed to  950 . At  950 , method  900  may include commanding fully closed the CPV, and commanding the ELCM COV in the first position (refer to  FIG. 3C ). In this way, pressure in the evaporative emissions system may be relieved. 
     Proceeding to  955 , method  900  may include indicating whether conditions are still met for obtaining baseline or test data. For example, if baseline data was being acquired, then conditions being met at  955  relate to conditions being met for obtaining further baseline data. If test data was being acquired, then conditions being met at  955  relate to conditions being met for obtaining further test data. Conditions being met at  955  may include an indication that the intake manifold vacuum remains unchanged from the baseline or test data acquired prior to step  955 . 
     If, at  955 , conditions are no longer met for obtaining the baseline or test data, method  900  may proceed to  960 . At  960 , method  900  may include aborting the procedure, and may further include updating a schedule for conducting onboard CPV flow test diagnostic(s) to reflect the aborted test procedure. For example, another CPV onboard flow test may be scheduled for the next possible situation where conditions are met for conducting such a test. 
     Returning to  955 , if conditions are indicated to be met for obtaining further baseline or test CPV flow data, method  900  may proceed to  965 . At  965 , method  900  may include repeating the steps  925  through  950 , but instead of cycling the CPV at the first rate, the CPV may be cycled at a second rate (e.g. 10% duty cycle). 
     As discussed with regard to method  900 , the results of the baseline or test CPV flow measurements may be stored at the controller. Responsive to both baseline and test measurements having been obtained, method  800  at step  825  may be used to determine the CPV degradation factor, in order to adjust CPV flow maps such that future purging events may be more accurately controlled to reflect requested purge flow rates, as discussed in detail above. 
     Turning now to  FIG. 10 , if at  FIG. 9  the engine was not indicated to be combusting air and fuel, method  900  may proceed to method  1000  where at step  1005  it may be indicated as to whether conditions are met for conducting a diagnostic for obtaining baseline or test CPV flow data under conditions where the engine is not combusting air and fuel. Accordingly, at  1005 , method  1000  may include indicating whether conditions are met for obtaining such baseline or test CPV flow measurements. Conditions being met may include an indication of a fuel vapor canister load less than a threshold load. The threshold load may include a canister load of less than 5% capacity, less than 1% capacity, etc. In other words, conditions being met may include an indication that the canister is clean, so as not to introduce fuel vapors to the engine while the engine is not combusting air and fuel. Conditions being met may include a start/stop event, for example where the engine is stopped from combusting air and fuel. In some examples, conditions being met may include an indication that the vehicle is not in motion, for example. In other words, conditions being met may include an indication that the vehicle is not being propelled by power from the onboard energy storage device. However, in other examples, the vehicle may be in motion, being propelled via energy from the onboard energy storage device, without departing from the scope of this disclosure. In some examples, conditions being met may include an indication of a key-off event where the controller is kept in an awake mode to conduct such a diagnostic to obtain baseline or test CPV flow measurements. In still other examples, the controller may be scheduled to awake at a predetermined time after a key-off event, to conduct such a diagnostic. 
     Still further, similar to that discussed above at  FIG. 9 , conditions being met for specifically obtaining baseline CPV flow data may include an indication that the CPV is within a threshold amount of time from being installed in the vehicle (e.g. less than 1 day, less than 2 days, etc.), or in other words, no indication of CPV degradation, no indication of evaporative emissions system degradation, etc. Conditions being met for specifically obtaining test CPV flow data may include an indication that a threshold duration of time has elapsed since baseline measurements were obtained, or a threshold duration of time since prior test measurements were obtained, an indication of CPV degradation to some extent, etc. Conditions being met for obtaining test measurements may include an indication of no sources of undesired evaporative emissions in the vehicle evaporative emissions system (however in other examples conditions being met may include an indication of a source of undesired evaporative emissions stemming from the evaporative emissions system), no indication of ELCM degradation, no indication of FTIV degradation, etc. 
     If, at  1005 , conditions are not indicated to be met for conducting the diagnostic to obtain the baseline or test CPV flow measurements, method  1000  may proceed to  1010 , where current vehicle operating parameters may be maintained. Method  1000  may then end. 
     Alternatively, if conditions are indicated to be met at  1005 , method  1000  may proceed to  1015 . At  1015 , it may be determined as to whether conditions are met for conducting the diagnostic via the purge pump (e.g.  299 ). For example, if a purge pump is not included in the vehicle system, then conditions may not be met for conducting the diagnostic via the purge pump. In another example, if the purge pump is indicated to be degraded, then conditions may not be met for conducting the diagnostic via the purge pump. In still another example, if CPV flow data per the purge pump is not requested at such a time, for example if sufficient data has already been acquired to enable a CPV degradation factor specific to the purge pump for updating a CPV flow map that is based on use of the purge pump for purging events, then conditions may not be met at  1015 . 
     Responsive to conditions not being met at  1015 , method  1000  may proceed to  1020 , where the diagnostic for obtaining CPV flow data may be conducted via the method depicted at  FIG. 11 . However, responsive to conditions being met at  1015 , method  1000  may proceed to  1025 . At  1025 , the purge pump may be activated to a predetermined speed. The predetermined speed may comprise a speed for which CPV flow data is requested, and the predetermined speed may be different for different diagnostics that make use of the purge pump. For example,  FIG. 7B  illustrates different purge pump speeds utilized for obtaining CPV flow degradation factors, thus the predetermined speed may vary depending on which data (at which speed) has already been obtained, and which data still is requested to be obtained. 
     Activating the purge pump at  1025  may include activating the purge pump to draw vacuum on the fuel vapor storage canister. In other words, the purge pump may be activated in the forward direction. To avoid pressure build between the CPV and the purge pump, the purge pump bypass valve (e.g.  299   c ) may be commanded open initially while the pump achieves the desired speed. Proceeding to step  1030 , the ELCM COV may be commanded to the second position (refer to  FIG. 3E ), and at step  1035  the CPV may be commanded to be duty cycled at the first rate (e.g. 90% duty cycle). It may be understood that steps  1030  and  1035  may be performed near simultaneously, or in other words, within a threshold of each other (e.g. less than 1 second). Furthermore, while not explicitly illustrated, if the purge pump bypass valve is open, the purge pump bypass valve may be commanded closed at the same time as steps  1030  and  1035  are carried out. 
     Proceeding to  1040 , as discussed at method  900 , via the ELCM pressure sensor a rate at which vacuum in the evaporative emissions system builds to the predetermined vacuum (e.g. −20 InH2O) may be determined and stored at the controller. Responsive to the rate being determined, method  1000  may proceed to  1045 , where the purge pump may be deactivated, and vacuum in the evaporative emissions system may be relieved via commanding the ELCM COV to the first position (refer to  FIG. 3C ). Furthermore, at  1045 , the CPV may be commanded closed. 
     Proceeding to  1050 , method  1000  may include indicating whether conditions are still met for obtaining the baseline or test data. Conditions being met at  1050  may include an indication that vehicle operating conditions have not changed which may adversely impact the baseline or test measurements. For example, if the test was being conducted during a S/S event and the engine has been activated in response to an acceleration request via a vehicle operator, then conditions may not be met at  1050 . In another example, if the baseline or test measurements were being obtained during a key-off condition and the vehicle has become occupied and started, either in an engine-on or in some examples, engine-off manner, conditions may not be continued to be met at  1050 . 
     If, at  1050 , conditions are not still met for obtaining baseline or test data, then method  1000  may proceed to  1055 . At  1055 , method  1000  may include aborting the procedure, and updating a diagnostic test schedule for conducting onboard CPV flow test diagnostic(s) to reflect the aborted test procedure. For example, another CPV onboard flow test may be scheduled for the next possible situation where conditions are met for conducting such a test. 
     Returning to  1050 , if conditions are indicated to be met for obtaining further baseline or test CPV flow data, method  1000  may proceed to  1060 . At  1060 , method  1000  may include repeating steps  1025 - 1045 , but instead of duty cycling the CPV at the first rate, the CPV may be cycled at a second rate (e.g. 10% duty cycle). 
     As discussed with regard to method  1000 , the results of the baseline or test CPV flow measurements obtained may be stored at the controller. Responsive to both baseline and test measurements having been obtained, method  800  at step  825  may be used to determine the CPV degradation factor, in order to adjust CPV flow maps such that future purging events may be more accurately controlled to reflect requested purge flow rates. 
     Turning now to  FIG. 11 , if at  FIG. 10  conditions were not indicated to be met for obtaining the CPV flow measurements via use of the purge pump, method  1000  may proceed to method  1100  where at step  1105  it may be indicated as to whether conditions are met for conducting the diagnostic via unfueled engine rotation. Such conditions may be similar to those for conducting the diagnostic via the purge pump. For example, conditions being met may include an indication of a fuel vapor canister load less than a threshold load (e.g. less than 5%, or less than 1% capacity). Conditions being met may in some examples include a start/stop event where the engine is stopped from combusting air and fuel, an indication that the vehicle is not in motion (e.g. not being propelled solely via power from the onboard energy storage device), a key-off event where the controller is kept awake to conduct the diagnostic, a key-off event where the controller is awakened at a predetermined time since a key-off event to conduct the diagnostic, etc. However, in some examples, the diagnostic may be conducted with the vehicle in motion, being propelled solely by energy from the energy storage device, without departing from the scope of the present disclosure. 
     Still further, similar to that discussed above at  FIG. 11 , conditions being met for specifically obtaining baseline CPV flow data may include an indication that the CPV is within a threshold amount of time from being installed in the vehicle (e.g. less than 1 day, less than 2 days, etc.), or in other words, no indication of CPV degradation. Conditions being met for specifically obtaining baseline CPV flow data may include an indication of an absence of evaporative emissions system degradation. Conditions being met for specifically obtaining test CPV flow data may include an indication that a threshold duration of time has elapsed since baseline measurements were obtained, or a threshold duration of time since prior test measurements were obtained, an indication of CPV degradation to some extent, etc. Conditions being met for obtaining test CPV flow data may include an indication of no sources of undesired evaporative emissions in the vehicle evaporative emissions system (however in other examples conditions being met may include an indication of a source of undesired evaporative emissions in the evaporative emissions system), no indication of ELCM degradation, no indication of FTIV degradation, etc. 
     If, at  1105 , conditions are not indicated to be met for conducting the diagnostic via unfueled engine rotation, method  1100  may proceed to  1110 , where current vehicle operating parameters may be maintained. Method  1100  may then end. 
     Alternatively, if at  1105 , conditions are indicated to be met, method  1100  may proceed to  1115 . At  1115 , method  1100  may include commanding an intake throttle to a predetermined position. Such a predetermined position may comprise a position that the throttle is commanded to any time that unfueled engine rotation is used to obtain baseline or test CPV flow data. In some examples such a predetermine position may comprise the throttle being commanded to 50% closed, 60% closed, 75% closed, 85% closed, 95% closed, or 100% closed (e.g. fully closed). By controlling throttle position, it may be ensured that intake manifold vacuum as a result of unfueled engine rotation may be communicated effectively to the evaporative emissions system when the CPV is duty cycled to obtain the baseline or test measurements. 
     Proceeding to  1120 , method  1000  may include rotating the engine unfueled in a forward direction, where the forward direction comprises a direction that the engine rotates when combusting air and fuel. In other words, the rotation of the engine in the forward direction may result in development of a positive pressure with respect to atmospheric pressure in the exhaust system and a negative pressure with respect to atmospheric pressure in the intake manifold. Rotating the engine unfueled may comprise commanding a motor (e.g.  120 ) to rotate the engine, without providing spark and without providing fuel injection. 
     At  1120 , the engine may be rotated at a particular speed (RPM) and intake manifold vacuum monitored, for example via a MAP sensor (e.g.  213 ) with respect to a pressure in the evaporative emissions system. Engine speed may be controlled such that intake manifold vacuum is controlled to a predetermined intake manifold vacuum, such a vacuum specific to diagnostic being conducted. For example, returning to  FIG. 7A , various levels of intake manifold are depicted, and thus, engine speed may be controlled such that the desired intake manifold vacuum is achieved. As discussed, such an intake manifold vacuum may be referenced to pressure in the evaporative emissions system coupled to atmosphere, and may further be referenced to barometric pressure. 
     With the predetermined intake manifold vacuum established, method  1100  may proceed to  1125 . At  1125 , method  1100  may include configuring the ELCM COV (e.g.  315 ) in the second position (refer to  FIG. 3E ). Proceeding to  1130 , method  1100  may include duty cycling the CPV (e.g.  261 ) at a first rate (e.g. 90% duty cycle). At  1135 , method  1100  may include recording the rate at which vacuum builds in the evaporative emissions system to a predetermined vacuum level (e.g. −20 InH2O), as monitored by the ELCM pressure sensor (e.g.  296 ). When the predetermined vacuum level is reached, the rate may be stored at the controller. 
     Proceeding to  1140 , method  1100  may include commanding closed the CPV, and commanding the ELCM COV to the first position (refer to  FIG. 3C ), to relieve the vacuum in the evaporative emissions system. In some examples the engine may be maintained on at  1140 , and method  1100  may proceed to step  1145 . However, in other examples the engine may be deactivated at step  1140 . 
     At  1145 , method  1100  may include indicating whether conditions are still met for obtaining baseline or test CPV flow data. Similar to that discussed above, if the previous steps of method  1100  were being conducted to obtain baseline CPV flow data, then conditions being met at  1145  relate to obtaining further baseline data. Alternatively, if the previous steps were being conducted to obtain test CPV flow data, then conditions being met at  1145  relate to obtaining further test data. 
     Conditions being met at  1145  may include no indication that vehicle operating conditions have changed which would adversely impact the diagnostic being conducted. For example, if the engine has been activated to combust air and fuel, if the vehicle was stopped and has been initiated to be propelled, even via solely battery power, conditions may not be indicated to be met. 
     In the case where conditions are no longer indicated to be met at  1145 , method  1100  may proceed to  1150 . At  1150 , method  1100  may include aborting the procedure, and updating a diagnostic test schedule for conducting onboard CPV flow test diagnostic(s) to reflect the aborted test procedure. For example, another CPV onboard flow test may be scheduled for the next possible situation where conditions are met for conducting such a test. 
     Returning to  1145 , if conditions are indicated to be met for obtaining further baseline or test CPV flow data, method  1100  may proceed to  1155 . At  1155 , method  1100  may include repeating steps  1115 - 1140 , but instead of cycling the CPV at the first rate, the CPV may be cycled at a second rate (e.g. 10% duty cycle). 
     Similar to that discussed above, the results of such baseline or test measurements obtained via method  1100  may be stored at the controller. Responsive to both baseline and test measurements having been obtained, method  800  at step  825  may be used to determine the CPV degradation factor, in order to adjust CPV flow maps such that future purging events may be more accurately controlled to reflect requested purge flow rates. 
     Turning now to  FIG. 12 , an example timeline  1200  for conducting an engine on diagnostic to obtain test CPV flow measurements as per method  900  depicted at  FIG. 9 , is shown. More specifically, regarding example timeline  1200  it may be understood that baseline measurements have already been obtained and stored at the controller, at a plurality of intake manifold vacuum levels, and thus test measurements for one particular intake manifold vacuum level are being obtained according to example timeline  1200 . 
     Timeline  1200  includes plot  1205 , indicating a status of the engine (on or off), over time. The engine being on refers to the engine rotating, whereas the engine being off refers to the engine not rotating. Timeline  1200  further includes plot  1210 , indicating whether fuel injection to the engine is being provided (on) or not (off), over time. Timeline  1200  further includes plot  1215 , indicating a status (open or closed) of a canister purge valve (CPV), over time. It may be understood that a closed CPV refers to a fully closed CPV, and an open CPV refers to a fully open CPV. Timeline  1200  further includes plot  1220 , indicating a level of vacuum or negative pressure with respect to atmospheric pressure (atm.) in an intake manifold of the engine, over time. Timeline  1200  further includes plot  1225 , indicating pressure in an evaporative emissions system, over time. In this example, pressure may be at or near atmospheric pressure (atm.), or may be negative (vac.) with respect to atmospheric pressure. Timeline  1200  further includes plot  1230 , indicating whether an ELCM COV (e.g.  315 ) is in a first position (refer to  FIG. 3C ), or second position (refer to  FIG. 3E ), over time. Timeline  1200  further includes plot  1235 , indicating whether conditions are indicated to be met for conducting the diagnostic to obtain test measurements via methodology where the engine is combusting air and fuel, over time. Timeline  1200  further includes plot  1240 , indicating whether a FTIV (e.g.  252 ) is in an open or closed state, over time. 
     At time t 0 , the engine is on (plot  1205 ), and fuel injection is being provided (plot  1210 ). The CPV is closed (plot  1215 ), and the pressure in the intake manifold is near atmospheric pressure (plot  1220 ). The FTIV is also closed (plot  1240 ), and the ELCM COV is configured in the first position (plot  1230 ). Accordingly, pressure in the evaporative emissions system is near atmospheric pressure (plot  1225 ). At time t 0 , conditions are not yet indicated to be met for conducting the diagnostic for obtaining test CPV flow measurements. 
     Between time t 0  and t 1 , pressure in the intake manifold decreases, and stabilizes. It may be understood that the level of vacuum in the intake manifold corresponds to a vacuum level for which it is desirable to obtain test CPV flow measurements. For example, such a vacuum level may comprise a predetermined vacuum level for which test CPV flow measurements are requested via the controller. With the vacuum stabilized, at time t 1 , conditions are indicated to be met (plot  1235 ) for obtaining the test CPV flow measurements. Conditions being met at time t 1  may additionally include a variety of other variables being satisfied as per step  915  of method  900 . 
     With conditions being indicated to be met for obtaining the test CPV flow measurements, the CPV is commanded to be duty cycled at a first rate (e.g. 90%) (plot  1215 ), and the ELCM COV is commanded to the second position (plot  1230 ) to seal the evaporative emissions system from atmosphere. With the CPV being duty cycled, engine intake manifold vacuum may be communicated to the sealed evaporative emissions system, which may result in development of vacuum, as discussed. While not explicitly illustrated, in a case where the vehicle system includes a purge pump (e.g.  299 ), a purge pump bypass valve (e.g.  299   c ) may be commanded fully open concurrent with the commanding the ELCM COV to the second position and commanding the CPV to be duty cycled. 
     Between time t 1  and t 2 , pressure in the evaporative emissions system, as monitored by an ELCM pressure sensor (e.g.  296 ), is reduced (plot  1225 ), and at time t 2 , the vacuum builds to a predetermined threshold vacuum (e.g. −20 InH2O), represented by line  1226 . Accordingly, at time t 2 , the rate at which the pressure was reduced to the predetermined threshold vacuum is stored at the controller. 
     At time t 2 , the ELCM COV is commanded to the first position (plot  1230 ), and the CPV is stopped from being duty cycled (plot  1215 ). With the CPV closed and the ELCM COV configured in the first position, pressure in the evaporative emissions system returns to atmospheric pressure between time t 2  and t 3 . 
     At time t 3 , conditions are still indicated to be met for obtaining further test CPV flow data. Importantly, the intake manifold vacuum remains essentially constant, which is a stipulation for obtaining further CPV flow data. In some examples, for an engine equipped with twin-independent variable cam timing, intake manifold vacuum may be maintained constant via manipulation of actuators (e.g.  483 ,  484 ) controlling intake and/or exhaust valves of the engine. Furthermore, in some examples, intake manifold vacuum may be maintained constant via additionally or alternatively using a motor (e.g.  120 ) to assist the engine in meeting vehicle operator-requested torque requests such that intake manifold may be maintained constant for conducting the diagnostic. 
     With conditions still being indicated to be met at time t 3 , the ELCM COV is commanded to the second position (plot  1230 ), and the CPV is duty cycled at a second rate (e.g. 10%) (plot  1215 ). Accordingly, pressure in the evaporative emissions system again is reduced between time t 3  and t 4 , but at a slower rate than the rate between time t 1  and t 2 . At time t 4 , the vacuum builds to the predetermined vacuum threshold, and the rate at which the vacuum built to the predetermined vacuum threshold is stored at the controller. At time t 4 , the CPV is commanded closed (plot  1215 ), or in other words is stopped from being duty cycled, and the ELCM COV is commanded to the first position (plot  1230 ). With test data having been obtained for the particular intake manifold vacuum level at two different duty cycles, conditions are no longer indicated to be met for conducting the diagnostic (plot  1235 ), or in other words. Accordingly, between time t 4  and t 5  pressure in the evaporative emissions system returns to atmospheric pressure (plot  1225 ), and intake manifold vacuum is a function of driver demand. 
     While test measurements corresponding to one intake manifold vacuum are illustrated at  FIG. 12 , it may be understood that such test measurements may be obtained in similar fashion for other intake manifold vacuum levels, where such intake manifold vacuum levels may correspond to intake manifold vacuum levels for which baseline CPV flow measurements were obtained. In this way, a plot similar to that depicted at  FIG. 7A  may be generated, and a CPV degradation factor may be determined, as discussed in detail above and with regard to  FIG. 8 . 
     Turning now to  FIG. 13 , an example timeline  1300  depicting a diagnostic using a purge pump to obtain test CPV flow measurements, is shown. More specifically, for example timeline  1300  it may be understood that baseline CPV flow measurements have already been obtained at various purge pump speeds, and thus test CPV flow measurements are requested. Timeline  1300  includes plot  1305 , indicating engine status (on or off), and plot  1310 , indicating whether fuel injection is being provided (on) or not (off) to the engine, over time. Timeline  1300  further includes plot  1315 , indicating position of an air intake throttle (open or closed), over time. In this example it may be understood that the throttle being open refers to the throttle being fully open, whereas the throttle being closed refers to the throttle being fully closed. Timeline  1300  further includes plot  1320 , indicating status of a purge pump (e.g.  299 ) (on or off), over time. In this example, it may be understood that the purge pump being “on” may include the purge pump being activated to a predetermined speed, the predetermined speed corresponding to a speed for which the test CPV flow measurements are desired. 
     Timeline  1300  further includes plot  1325 , indicating a status of a CPV (e.g.  261 ), over time. The CPV may be fully open or fully closed. Timeline  1300  further includes plot  1330 , indicating pressure in an evaporative emissions system, over time. In this example timeline, pressure in the evaporative emissions system may be near atmospheric pressure (atm.), or may be negative (vac.) with respect to atmospheric pressure. Timeline  1300  further includes plot  1335 , indicating a position of an ELCM COV (e.g.  315 ), over time. The ELCM COV may be in either a first position (refer to  FIG. 3C ), or may be in a second position (refer to  FIG. 3E ). Timeline  1300  further includes plot  1340 , indicating whether conditions are met for conducting an engine-off diagnostic for test CPV flow measurements via the purge pump, over time. Timeline  1300  further includes plot  1345 , indicating a status of an FTIV (e.g.  252 ), over time. 
     At time t 0 , the engine is on (plot  1305 ), and combusting air and fuel, as fuel is being provided to the engine (plot  1310 ). The throttle is controlled to a position based on driver demand (plot  1315 ). The purge pump is off (plot  1320 ), and the CPV is closed (plot  1325 ). Pressure in the evaporative emissions system is near atmospheric pressure (plot  1330 ), as the ELCM COV is configured in the first position (plot  1335 ) and the FTIV is closed (plot  1345 ). Conditions are not yet indicated to be met for conducting the diagnostic to obtain test CPV flow measurements via the purge pump, as the engine is in operation. It may be understood that it may not be requested to obtain test CPV flow measurements at time t 0  via the engine for a variety of reasons, including intake manifold vacuum at a level for which test CPV flow measurements are not requested, for example. 
     At time t 1 , the engine is deactivated, and fuel injection is discontinued. At time t 2 , conditions are indicated to be met for obtaining test CPV flow measurements via the purge pump. Accordingly, at time t 3 , the throttle is commanded to a fully open position (plot  1315 ), the ELCM COV is commanded to the second position (plot  1335 ), the purge pump is commanded on to a predetermined speed (plot  1320 ), the speed comprising a speed requested by the controller for obtaining test CPV flow measurements. Furthermore, at time t 3 , the CPV is commanded to be duty cycled at a first rate (e.g. 90% duty cycle) (plot  1325 ). It may be understood that the purge pump is activated in the forward-mode, such that a vacuum is drawn on the canister and evaporative emission system, and a positive pressure is delivered to the intake system. 
     While not explicitly illustrated, in some examples, between time t 2  and t 3 , the engine may be controlled via unfueled engine rotation to position intake valves in a closed configuration. For example, if the engine is configured with twin independent variable cam timing (Ti-VCT), then actuators (e.g.  483 ,  484 ) may be commanded such that intake valves of the engine may be controlled to be substantially closed, such that air flow is routed to atmosphere via the fully open throttle. However, in other examples, intake valves of the engine may not be controlled to the closed position without departing from the scope of this disclosure. 
     Still further, it may be understood that, while not explicitly illustrated, commanding on the purge pump may include commanding or maintaining closed a purge pump bypass valve (e.g.  299   c ). 
     Between time t 3  and t 4 , pressure in the evaporative emissions system is reduced via the purge pump as a function of duty cycle of the CPV. At time t 4 , a predetermined vacuum level (e.g. −20 InH2O) is reached, represented by line  1331 . The rate at which the predetermined vacuum level is reached is determined, and is stored at the controller. 
     At time t 4 , with the predetermined vacuum having been reached, the purge pump is deactivated, the CPV is commanded closed, and the ELCM COV is commanded to the first position. Accordingly, pressure in the evaporative emissions system returns to atmospheric pressure (plot  1330 ) between time t 4  and t 5 . 
     At time t 5 , conditions are still indicated to be met for obtaining further test CPV flow measurements. Accordingly, the purge pump is activated to the same speed, the ELCM COV is commanded to the second position, and the CPV is duty cycled at a second rate (e.g. 10%). Accordingly, between time t 5  and t 6  pressure in the evaporative emissions system is reduced at a slower rate than between time t 3  and t 4 . 
     At time t 6 , pressure in the evaporative emissions system reaches the predetermined vacuum threshold (e.g. −20 InH2O). The rate at which the pressure reached the predetermined vacuum is stored at the controller. With both rates for the first and second duty cycles having been determined, conditions are no longer indicated to be met for conducting the diagnostic to obtain the test CPV flow measurements (plot  1340 ). Accordingly, the throttle is returned to the position it was in prior to conducting the diagnostic, the purge pump is deactivated, the CPV is commanded or maintained closed, and the ELCM COV is commanded to the first position. Between time t 6  and t 7 , pressure in the evaporative emissions system returns to atmospheric pressure (plot  1330 ), and the engine is maintained off. 
     While test measurements corresponding to one purge pump speed are illustrated at  FIG. 13 , it may be understood that such test measurements may be obtained in similar fashion for other purge pump speeds, where such speeds may correspond to speeds for which baseline CPV flow measurements were obtained. In this way, a plot similar to that depicted at  FIG. 7B  may be generated, and a CPV degradation factor may be determined, as discussed in detail above and with regard to  FIG. 8 . 
     Turning now to  FIG. 14 , an example timeline  1400  for obtaining test CPV flow measurements via unfueled engine rotation, is shown. More specifically, for example timeline  1400  it may be understood that baseline CPV flow measurements obtained via unfueled engine rotation have already been obtained, and thus test CPV flow measurements are currently requested. Timeline  1400  includes plot  1405 , indicating a status of the engine, over time. The engine may either be on, or off, where the engine being on refers to the engine rotating in a forward direction, or in other words, the same direction as the engine rotates when combusting air and fuel. 
     Timeline  1400  further includes plot  1410 , indicating whether fuel injection is being provided to the engine (on) or not (off), over time. Timeline  1400  further includes plot  1415 , indicating a position of an air intake throttle, over time. The throttle may be fully open, fully closed, or somewhere between. Timeline  1400  further includes plot  1420 , indicating pressure in an intake manifold of the engine, over time. In this example timeline, pressure may be near atmospheric pressure (atm.), or may be negative (vac.) with respect to atmospheric pressure. Timeline  1400  further includes plot  1425 , indicating a status of a CPV, over time. The CPV may be either fully open or fully closed. Timeline  1400  further includes plot  1430 , indicating pressure in an evaporative emissions system, over time. Pressure in the evaporative emissions system in this example timeline may be near atmospheric pressure, or may be negative (vac.) with respect to atmospheric pressure. Timeline  1400  further includes plot  1435 , indicating a position of an ELCM COV (e.g.  315 ), over time. The ELCM COV may either be in a first position (refer to  FIG. 3C ), or a second position (refer to  FIG. 3E ), over time. Timeline  1400  further includes plot  1440 , indicating whether conditions are met for obtaining test CPV flow measurements via unfueled engine rotation, over time. Timeline  1400  further includes plot  1445 , indicating a status (open or closed) of an FTIV (e.g.  252 ), over time. 
     At time t 0 , the engine is on (plot  1405 ) and is combusting air and fuel (plot  1410 ). Throttle position (plot  1415 ) is a function of driver demand, as is intake manifold vacuum (plot  1420 ). The CPV is closed (plot  1425 ), the FTIV is closed (plot  1445 ), and the ELCM COV is configured in the first position (plot  1435 ). Accordingly, pressure in the evaporative emissions system is near atmospheric pressure (plot  1430 ). At time t 0 , with the engine in operation combusting air an fuel, conditions are not yet met for obtaining test CPV flow measurements via unfueled engine rotation. 
     At time t 1 , the engine is deactivated, and fuel injection is discontinued. Between time t 1  and t 2 , pressure in the intake manifold returns to atmospheric pressure. At time t 2 , conditions are indicated to be met for obtaining test CPV flow measurements via unfueled engine rotation. In this example, it may be understood that either a purge pump is not included in the vehicle, or the purge pump is indicated to be degraded, for example. 
     With conditions met for obtaining the test CPV flow measurements, at time t 3  the throttle is commanded to a predetermined position for obtaining the measurements, and the engine is activated to rotate in the forward direction (plot  1405 ), without fueling being provided (plot  1410 ). In other words, the engine is rotated unfueled via a motor (e.g.  120 ). It may be understood that the engine speed may be controlled to achieve a desired intake manifold vacuum, and in some examples, in conjunction with or alternatively via controlling the throttle. 
     Between time t 2  and t 3 , pressure in the intake manifold reaches a desired level of intake manifold vacuum. In other words, the controller may request a particular vacuum for which test CPV flow data is desired, and the engine may be rotated to achieve said vacuum. With the desired vacuum reached and maintained, for example via controlling engine speed and/or throttle position, at time t 3  the ELCM COV is commanded to the second position (plot  1435 ), and the CPV is duty cycled at a first rate (e.g. 90%). While not explicitly illustrated, in a case where the vehicle includes a purge pump, a purge pump bypass valve (e.g.  299   c ) may be commanded open at time t 3 . 
     Between time t 3  and t 4 , pressure in the evaporative emissions system is reduced, and at time t 4  pressure reaches a predetermined threshold vacuum (e.g. −20 InH2O). A rate at which the predetermined threshold vacuum was reached may be stored at the controller. With the rate determined for the first CPV duty cycle, the ELCM COV is commanded to the first position, and the CPV is commanded closed. Between time t 4  and t 5  pressure in the evaporative emissions system returns to atmospheric pressure. 
     At time t 5 , conditions are still indicated to be met for obtaining further test CPV flow measurements for the current intake manifold vacuum level. Accordingly, the ELCM COV is again commanded to the second position and the CPV is duty cycled at a second rate (e.g. 10%). Accordingly, pressure in the evaporative emissions system is reduced at a slower rate than between time t 3  and t 4 . At time t 6 , pressure in the evaporative emissions system reaches the predetermined threshold vacuum (e.g. −20 In H2O), and the rate at which the predetermined threshold vacuum was reached is stored at the controller. With both rates obtained for the two CPV duty cycles, conditions are no longer indicated to be met for conducting the diagnostic, the engine is deactivated, the throttle is returned to its position it was in prior to the diagnostic, the CPV is commanded or maintained closed, and the ELCM COV is commanded to the first position. Accordingly, between time t 6  and t 7 , pressure in the evaporative emissions system returns to atmospheric pressure, as does pressure in the intake manifold. 
     Again, while test measurements corresponding to one intake manifold vacuum are illustrated at  FIG. 14 , it may be understood that such test measurements may be obtained in similar fashion for other intake manifold vacuums, where such vacuums may correspond to vacuums for which baseline CPV flow measurements were obtained. In this way, a plot similar to that depicted at  FIG. 7A  may be generated, and a CPV degradation factor may be determined, as discussed in detail above and with regard to  FIG. 8 . 
     Thus, a method controlling a duty cycle of a purge valve configured to regulate a purge flow from a fuel vapor storage canister to an intake of an engine during a canister purging event based on a degradation factor obtained by comparison of durations at which a predetermined pressure is reached in an evaporative emissions system at multiple purge valve activation levels. In such a method, the evaporative emissions system may be sealed for obtaining the durations at which the predetermined pressure is reached. In such a method, the predetermined pressure may comprise a negative pressure with respect to atmospheric pressure. Furthermore, a fuel system may be sealed from the evaporative emissions system for obtaining the durations at which the predetermined pressure is reached. 
     In such a method, the comparison of the durations at which the predetermined pressure is reached at multiple purge valve activation levels may include both conditions for which there is an absence of evaporative emissions system degradation and conditions for which there is a presence of evaporative emissions system degradation. 
     Such a method may further comprise operating a pump positioned downstream of the fuel vapor storage canister to communicate a predetermined vacuum to the evaporative emissions system for obtaining the durations at which the predetermined pressure is reached. In one example, the pump comprises the engine. In another example, the pump comprises a purge pump positioned in a purge line between the purge valve and the fuel vapor storage canister. 
     In such a method, the predetermined pressure that is reached may be monitored via a pressure sensor positioned in the evaporative emissions system configured to indicate pressure across a reference orifice in the evaporative emissions system. The multiple purge valve activation levels may include two or more different duty cycles of the purge valve. Furthermore, the degradation factor may be used to adjust a flow map for controlling the duty cycle of the purge valve during the canister purging event. 
     Another example of a method comprises updating a flow map at a controller of a vehicle based on an onboard diagnostic that compares a set of test rates at which a predetermined vacuum is reached in a sealed evaporative emissions system to a set of baseline rates at which the predetermined vacuum is reached in the sealed evaporative emissions system; and controlling a purge valve positioned between a fuel vapor storage canister and an engine during a purging event where fuel vapors are purged from the fuel vapor storage canister to the engine, based on the updated flow map. 
     In such a method, the set of baseline rates are obtained under conditions of an absence of degradation of the purge valve and evaporative emissions system, and the test rates are obtained at a time subsequent to obtaining the baseline rates. 
     In such a method, the onboard diagnostic includes duty cycling the purge valve at a first rate and then a second rate while predetermined negative pressure with respect to atmosphere is applied on the evaporative emissions system from a position downstream of the fuel vapor storage canister, for obtaining the set of test rates and the set of baseline rates. The method may further comprise maintaining the predetermined negative pressure substantially constant when duty cycling the purge valve at the first rate and then the second rate, and where more than one negative pressure may be used to obtain the set of test rates and the set of baseline rates by duty cycling the purge valve at the first rate and the second rate. 
     In such a method, a degradation factor may be obtained by comparing the set of test rates to the set of baseline rates, and the degradation factor may be used to update the flow map at the controller. The flow map may be relied upon for controlling the purge valve in response to a requested flow rate of air and fuel vapor from the fuel vapor storage canister to the engine for the purge event. 
     As discussed, one approach for indicating CPV degradation may include monitoring pressure in the evaporative emissions system while the engine is combusting air and fuel and where the CPV is commanded closed with the evaporative emissions system sealed. If a negative pressure from the intake manifold is communicated to the evaporative emissions system, as monitored via a pressure sensor (e.g.  296 ), then it may be indicated that the CPV is degraded. In another example, a similar approach of communicating negative pressure from the intake manifold (with the engine combusting) to the evaporative emissions system and monitoring pressure therein, may be conducted with the CPV open and the evaporative emissions system sealed from atmosphere. In this example, a lack of vacuum or a substantially reduced vacuum may be indicative of degradation in the form of a CPV that is sticking closed, that there is a large source of undesired evaporative emissions stemming from the evaporative emissions system, that there is a restriction in the evaporative emissions system (e.g. canister internal filter (e.g.  297 ) restriction), etc. 
     Such examples rely on the engine combusting air and fuel in order to be conducted. However, hybrid vehicles (e.g. plug-in hybrid electric vehicles, stop/start, hybrid electric vehicles, etc.) may have limited run time and thus limited opportunities to conduct such tests. Thus, other approaches may be desirable for vehicles with limited engine run time. 
     It is desirable that such an approach enable a determination of potential CPV degradation (e.g. improper sealing or improper opening), potential canister internal filter restriction, etc. As one example, the canister filter may become clogged or plugged to various extents over time, and such a condition may impact the ability to purge, and which may be a factor in the CPV flow test diagnostics described above. In other words, adjusting a CPV flow map as discussed above may serve to account for a level to which the internal filter is clogged or plugged in addition to or alternative to any CPV degradation. Any indication of CPV degradation, or any indication of the canister internal filter being clogged/plugged, may be used as an entry condition for conducting the CPV flow mapping diagnostics as discussed above. Thus, a method for providing such indication(s) is discussed in detail below with regard to  FIGS. 15-16 . Such a diagnostic may be referred to as a evap flow diagnostic, as the diagnostic relates to whether a purge flow (for example during purging the canister) through the evaporative (evap) emissions system may be impacted by a current status of the CPV, canister internal filter, and evaporative emissions system in general. In examples where a purge pump is included in the vehicle system, such a diagnostic may further relate to whether a purge pump bypass valve or conduits routing fluid flow around the purge pump, may be degraded. 
     Accordingly, turning to  FIG. 15 , a high-level example method  1500  for diagnosing whether a CPV may be degraded to some extent and/or whether a canister internal filter may be clogged or plugged to some extent, is shown. Specifically, the method includes conducting the diagnostic during a refueling event, where fluid flow induced via the refueling event (e.g. induced via the generation of pressure during refueling) is used as a means for assessing evaporative emissions system degradation (e.g. one or more of canister internal filter degradation, CPV degradation, purge line degradation, purge pump bypass valve degradation (where included), purge pump bypass conduit degradation, etc.). To indicate the presence or absence of such degradation, fluid flow in an intake of the engine induced by the refueling event may be relied upon, for example via a monitoring of the fluid flow via a mass air flow (MAF) sensor (e.g.  202 ) positioned in an intake of the engine. 
     Method  1500  will be described with reference to the systems described herein and shown in  FIGS. 1-4 , though it will be appreciated that similar methods may be applied to other systems without departing from the scope of this disclosure. Instructions for carrying out method  1500  and the rest of the methods included herein may be executed by a controller, such as controller  212  of  FIG. 2 , based on instructions stored in non-transitory memory, and in conjunction with signals received from sensors of the engine system, such as temperature sensors, pressure sensors, and other sensors described in  FIGS. 1-4 . The controller may employ actuators such as CPV (e.g.  261 ), purge pump bypass valve (e.g.  299   c ) (where included), throttle (e.g.  262 ), etc., according to the methods described herein. 
     Method  1500  begins at  1505 , and may include, during a refueling event where fuel is being added to the fuel tank, conducting a baseline evap flow diagnostic responsive to conditions being met for doing so. For example, the baseline evap flow diagnostic may be conducted under conditions where it is known that there is no degradation of the CPV, purge line, and that the canister internal filter is clean (e.g. loading of the canister internal filter with debris below a threshold loading amount). In a situation where the vehicle system includes a purge pump, the baseline evap flow diagnostic may further include an indication that the purge pump bypass valve and purge pump bypass conduits are not degraded. 
     The baseline evap flow diagnostic may be conducted as follows. During refueling, an FTIV (e.g.  252 ) may be opened to enable refueling vapors to be directed to the canister. The CPV may be maintained closed. Provided that during the refueling event, pressure in the fuel system/evaporative emissions system does not increase above a threshold and/or there are no indications of premature shutoffs that would indicate the canister itself is clogged/restricted, or that the air filter (e.g.  259 ) upstream of the canister is clogged/restricted, the CPV may be commanded open and air flow in the intake of the engine may be monitored. To enable such fluid flow, an intake throttle may be additionally commanded fully open. The fluid flow may be monitored via the MAF sensor as the flow proceeds from the fuel tank, through the open CPV and to the intake. Such fluid flow may thus constitute baseline evap flow measurements. For example, the fluid flow may be monitored for a predetermined time duration, and then may be averaged or otherwise processed to yield the baseline evap flow. For consistency, conditions being met for conducting the baseline evap flow diagnostic may include a pressure in the fuel system being within a threshold of a desired fuel system pressure during refueling (e.g. a pressure corresponding to 10 gallons per minute being provided via a refueling dispenser). Subsequent to the baseline evap flow measurements having been obtained, the CPV may be commanded closed and the throttle returned to the position it was in prior to the obtaining of the baseline evap flow measurements. 
     With such baseline evap flow measurements having been obtained at  1505 , method  1500  may proceed to  1510 , where said baseline evap flow measurements (or the processed versions thereof) may be stored at the controller. 
     Proceeding to  1515 , at a later time, for example after a predetermined time duration has elapsed since the baseline evap flow measurements were obtained, or according to a predetermined schedule for conducting the diagnostic, method  1500  may include obtaining test evap flow measurements similar to that described above for obtaining the baseline evap flow measurements. However, for the test measurements, conditions being met to conduct the diagnostic may not include an indication that the canister internal filter is substantially clean, and may not include an indication that the CPV (and in some examples the purge pump bypass valve) is not degraded, as the diagnostic is specifically attempting to determine current operational state of such components. Briefly, during such a refueling event to obtain test evap flow measurements, again the CPV may be maintained closed and provided that no premature shutoffs are indicated and/or that pressure remains below the threshold pressure, and further that pressure in the fuel system is within the threshold of the desired fuel system pressure (e.g. a pressure corresponding to 10 gallons per minute being provided via a refueling dispenser), the CPV and throttle may each be commanded fully open (along with a purge pump bypass valve where included), and fluid flow in the intake may be monitored for the same predetermined time duration as that described above at step  1505 . The monitoring of the fluid flow may again be conducted via the MAF sensor, and the data may be averaged or otherwise processed after the predetermined time duration has elapsed. Such data may be stored at the controller at step  1520 . Again, after the predetermined time duration elapses, the CPV may be commanded closed (along with the purge pump bypass valve where included), and the throttle may be returned to the position it was in prior to obtaining the test evap flow measurements. 
     Proceeding to  1525 , method  1500  may include comparing the test evap flow measurements to the baseline evap flow measurements, to indicate the presence or absence of degradation. In this example, evaporative emissions system degradation may include one or more of CPV degradation (e.g. the CPV not fully opening or sticking closed), the canister internal filter being clogged/plugged to at least some extent, the purge pump bypass valve being degraded (where included), etc., when the test evap flow measurements as monitored via the MAF sensor are substantially less than the baseline evap flow measurements. In other words, comparing the test evap flow measurements to the baseline evap flow measurements at  1525  may include indicating that there is degradation as discussed above, provided the test evap flow measurements are not within a threshold (e.g. within 5% or within 1%) of the baseline evap flow measurements, for example. Alternatively, an absence of degradation may be indicated responsive to the test evap flow measurements being within the threshold of the baseline evap flow measurements. Method  1500  may then end. 
     Method  1500  thus represents a high-level example method of the diagnostic described above which may be used to compare the test evap flow measurements to the baseline evap flow measurements. A more detailed methodology is provided below with regard to  FIG. 16 . 
     Turning now to  FIG. 16 , a method  1600  for obtaining either the baseline evap flow measurements or the test evap flow measurements as discussed above with regard to  FIG. 15 , is shown. Only one method is illustrated because the methodology for obtaining baseline evap flow measurements is substantially the same as obtaining test evap flow measurements. Method  1600  begins at  1605 , and includes indicating whether a refueling event is in progress. Such an indication may be provided based on a request via a vehicle operator to commence refueling, and may additionally or alternatively include an indication that fuel is being added to the fuel tank (e.g. fuel level increasing as monitored via a fuel level indicator). If a refueling event is not in progress, method  1600  may proceed to  1610 , where current vehicle operating parameters may be maintained. Method  1600  may then end. 
     Returning to  1605 , responsive to an indication that a refueling event is in progress, method  1600  may include monitoring fuel system pressure. Such pressure may be monitored, for example, via a fuel tank pressure transducer (FTPT) (e.g.  291 ). Proceeding to  1620 , method  1600  may include indicating whether pressure in the fuel system is greater than the predetermined threshold and/or if premature shutoffs are indicated. If pressure in the fuel system is greater than the predetermined threshold and/or if premature shutoffs are indicated, method  1600  may proceed to  1625 . At  1625 , method  1600  may include indicating potential canister restriction and/or potential air filter (e.g.  259 ) restriction. With canister restriction and/or potential restriction of the air filter indicated, method  1600  may proceed to  1630 , where the refueling event may proceed, provided the premature shutoffs do not prevent the vehicle fuel tank from being refueled. In such an example, when the refueling is completed, method  1600  may proceed to  1635 , where vehicle operating conditions may be updated to reflect the indication of restriction in the canister and/or air filter. For example, updating vehicle operating conditions may include illuminating a malfunction indicator light (MIL) at the vehicle dash in order to alert a vehicle operator of a request to service the vehicle to address the potential restrictions. In some examples, a canister purge schedule may be updated, to reflect the potential restriction. For example, the canister may be prevented from being purged until the issue of the restriction has been remedied or may be purged more aggressively (for example only at increased manifold vacuums). Further, other diagnostics that rely on evacuation of the evaporative emissions system and/or fuel system may be postponed until the issue of the restriction has been remedied. Method  1600  may then end. 
     Returning to  1620 , in response to an indication that pressure in the fuel system is not greater than the predetermined threshold, and/or responsive to an indication of an absence of premature shutoff events of the refueling dispenser, method  1600  may proceed to  1640 . At  1640 , method  1600  may include indicating whether conditions are met for conducting either the baseline evap flow diagnostic or the test evap flow diagnostic, as discussed above with regard to  FIG. 15 . As discussed above, one example of conditions being met may include an indication that pressure in the fuel system comprises the desired fuel system pressure, or where pressure is within a threshold of the desired fuel system pressure. Other conditions for conducting either the baseline evap flow diagnostic or the test evap flow diagnostic are discussed above with regard to  FIG. 15  and apply to step  1640  of method  1600 . 
     If, at  1640 , conditions are not indicated to be met for conducting such a diagnostic, method  1600  may proceed to  1645 . At  1645 , method  1600  may include proceeding with the refueling event without conducting the evap flow diagnostic (either the baseline or test evap flow diagnostic). Proceeding to  1650 , method  1600  may include updating vehicle operating parameters after the refueling event has been completed. For example, a canister loading state may be updated to reflect the refueling event, fuel tank fill level may be updated, a canister purging scheduled may be updated to reflect the refueling event, etc. Method  1600  may then end. 
     Returning to  1640 , responsive to an indication that conditions are met for conducting either the baseline evap flow diagnostic or the test evap flow diagnostic, method  1600  may proceed to  1655 . At  1655 , method  1600  may include commanding fully open the throttle (e.g.  262 ). Proceeding to  1660 , method  1600  may include commanding fully open the CPV, for a predetermined duration of time. While not explicitly illustrated, in a case where a purge pump is included in the vehicle system, the purge pump bypass valve may be commanded fully open. In this way, the fuel tank may be fluidically coupled to engine intake and to atmosphere. 
     With the fuel tank fluidically coupled to engine intake and to atmosphere, method  1600  may proceed to  1665 . At  1665 , mass air flow in the intake may be monitored, via for example, a MAF sensor (e.g.  202 ). Mass air flow measurements may be acquired periodically, for example every 1 second, every 5 seconds, etc. Proceeding to  1670 , method  1600  may include recording the MAF measurements at the controller after the predetermined duration of time has elapsed. As discussed, in some examples the MAF measurements may be averaged or otherwise processed, for storage at the controller. Furthermore, it may be understood that any fuel vapors that may have been routed from the fuel tank to the intake may be adsorbed via the AIS HC trap (e.g.  294 ) positioned in the intake, prior to exiting to atmosphere. 
     Proceeding to  1675 , method  1600  may include commanding closed the CPV (and where applicable, commanding closed the purge pump bypass valve), and commanding the throttle to be returned to the position it was in prior to obtaining the MAF measurements. Continuing at  1680 , method  1600  may include enabling the refueling event to proceed as usual, in other words, without directing or routing any fluid flow to the intake. Such action may be maintained until the refueling event is completed, for example via an automatic shutoff of the refueling dispenser, via removal of the dispenser from the fuel filler nozzle, etc. It may be understood that, upon completion of the refueling event, for vehicle fuel systems that include an FTIV (e.g.  252 ), the FTIV may be commanded closed to seal the fuel system from the evaporative emissions system. 
     Proceeding to  1685 , method  1600  may include updating vehicle operating parameters responsive to completion of the refueling event. For example, canister loading state may be updated, fuel level may be updated, and a canister purging schedule may be updated to reflect the refueling event. 
     Continuing to  1690 , method  1600  may include, where applicable, utilizing the evap flow measurements obtained via method  1600  to determine whether degradation is present, as discussed above with regard to  FIG. 15 . For example, if baseline evap flow measurements were obtained, then nothing more may be done than the storing of the baseline measurements at the controller per step  1670 . Alternatively, responsive to test evap flow measurements being obtained, then method  1500  may be used to compare the test evap flow measurements to the baseline evap flow measurements, in order to indicate the presence or absence of degradation, as discussed above with regard to  FIG. 15 . In this way, a presence or absence of evaporative emissions system degradation may be indicated during the refueling event based on fluid flow in the intake of the engine. 
     Continuing to  FIG. 17 , an example timeline  1700  for conducting the evap flow test diagnostic during a refueling event, as discussed above with regard to  FIGS. 15-16 , is shown. Timeline  1700  includes plot  1705 , indicating whether refueling is requested via the vehicle operator, plot  1710 , indicating a fuel level in the fuel tank, plot  1715 , indicating an open or closed status of the CPV, plot  1720 , indicating an open or closed status of the throttle, plot  1725  indicating mass air flow in engine intake as monitored via the MAF sensor, plot  1730 , indicating pressure in the fuel system as monitored via the FTPT, plot  1735 , indicating on open or closed status of the FTIV, and plot  1740 , indicating whether degradation is present. Each of the above-mentioned plots are with respect to time. For the CPV, throttle, and FTIV, it may be understood that “open” refers to fully open, and “closed” refers to fully closed. Fuel level may increase (+) or decrease (−), MAF may increase (+) with respect to no flow ( 0 ), and fuel tank pressure may increase (+) with respect to atmosphere (Atm.). 
     At time t 0 , refueling is not requested (plot  1705 ), and fuel level is low (plot  1710 ). The CPV is closed (plot  1715 ), the throttle is more closed than open (plot  1720 ), and the FTIV is closed (plot  1735 ). There is no air flow in the intake (plot  1725 ), fuel tank pressure is positive with respect to atmosphere (plot  1730 ), and degradation (e.g. of the CPV, canister internal filter, etc.) is not indicated. In this example illustration, it may be understood that the purge pump is not included in the vehicle system. 
     At time t 1 , a refueling event is requested via the vehicle operator. For example, a refueling button on the vehicle dash is depressed. Accordingly, the FTIV is commanded open via the controller, and with the fuel tank fluidically coupled to atmosphere, pressure in the fuel system decays to atmospheric pressure between time t 1  and t 2 . At time t 2 , refueling is enabled, for example a refueling lock is commanded or allowed to open, enabling fuel to be added to the tank. Between time t 2  and t 3 , pressure in the fuel system rises and stabilizes at a threshold pressure represented by dashed line  1731 . In this example, it may be understood that the threshold pressure represents a pressure expected in the fuel system in response to a predetermined fuel flow rate (e.g. 10 gallons per minute). In other words, the pressure in the fuel system has reached and stabilized at the desired fuel system pressure for conducting the evap flow diagnostic during refueling, as discussed above with regard to  FIGS. 15-16 . Furthermore, between time t 2  and t 3 , no premature shutoffs of the refueling dispenser are indicated (as per the absence of pressure fluctuations in the fuel system indicating such events). Accordingly, the canister is free from restriction and the air filter is not clogged/restricted to any significant extent. 
     Thus, at time t 3 , a test evap flow diagnostic is initiated. It may be understood that the baseline evap flow diagnostic has already been previously conducted, and the MAF measurements obtained via the baseline evap flow diagnostic is represented by dashed line  1726 . 
     At time t 3 , the CPV is commanded fully open, as is the throttle. At time t 4 , fluid flow in the intake is indicated (plot  1725 ) via the MAF sensor (e.g.  202 ). Such fluid flow increases and stabilizes between time t 4  and t 5 . Furthermore, between time t 4  and t 5 , pressure in the fuel system decreases slightly as there is now an additional pathway for pressure build-up in the fuel system to be relieved (e.g. via the vent line and via the purge line). 
     At time t 5 , it may be understood that the predetermined time duration for obtaining the test evap flow measurements elapses. Accordingly, the test evap flow measurements are stored at the controller, and the CPV is commanded closed, while the throttle is commanded to the position it was in prior to conducting the test evap flow diagnostic. 
     As indicated, MAF for the test evap flow diagnostic is lower than the MAF for the baseline evap flow diagnostic. As discussed, such data is processed via method  1500  discussed above, and at time t 5 , degradation is indicated based on the comparison between test evap flow measurements and baseline evap flow measurements. 
     Between time t 5  and t 6 , after fluid flow is effectively sealed from the intake, refueling proceeds as before conducting the evap flow diagnostic. 
     In this example, because degradation is indicated, it may be understood that either the CPV may not be fully opening, or the canister internal filter may be clogged to some extent. As additional examples, there may be degradation in the purge line (e.g. a source of undesired evaporative emissions), such that fluid flow is not reaching the MAF sensor. In some examples there may be a combination of one or more of the above examples in terms of degradation. In some examples, if it is known that there is an absence of undesired evaporative emissions stemming from the evaporative emissions system as indicated, for example, by other onboard methodology, then it may be indicated that the source of degradation is one of the canister internal filter or the canister purge valve. Furthermore, in such a case where it is additionally known that the canister purge valve is not degraded to any significant extent, then such a method may pinpoint the canister internal filter as the source of degradation (e.g. canister internal filter being clogged). 
     In any case, such an indication may provide impetus for proceeding (when conditions are appropriate) with updating CPV flow maps based on the methodology depicted above at  FIGS. 8-11 . In this way, control of the CPV during purging events may be updated to reflect the current vehicle component conditions, to avoid stalling/hesitation or underperformance that may otherwise occur if the degradation is not taken into account for purging operations. 
     While not explicitly illustrated, there may be opportunity during a refueling event to indicate whether a CPV is not properly sealing. For example, if any air flow in the intake as monitored via the MAF sensor is indicated during refueling while the CPV is commanded closed, then it may be an indication of the CPV not being fully closed even when commanded to be. As one example, the evaporative emissions system may be briefly sealed during refueling, to encourage fluid flow through a CPV that is not fully closing. Furthermore, in such an example, the throttle may be commanded open to allow for fluid flow to the intake. More specifically, during refueling the evaporative emissions system may be sealed, and the throttle commanded open. Mass air flow in the intake may be monitored for a predetermined duration. No fluid flow in the intake, or in other words, fluid flow below a threshold, may indicate the CPV is properly sealing. Alternatively, fluid flow greater than a threshold may indicate the CPV is not properly sealing. Such a diagnostic may be conducted for a predetermined amount of time, and may include monitoring pressure in the fuel system/evaporative emissions system to avoid undesirable pressure build-up during the diagnostic. 
     While such an approach described above with regard to the methods of  FIGS. 15-16  may be useful, it may be desirable to additionally have methodology for indicating evaporative emissions system degradation (e.g. potential CPV degradation, canister internal filter restriction, etc.), which does not rely on a refueling event, and that does not rely on the engine combusting air and fuel. Accordingly, turning to  FIG. 18 , a high level example method  1800  for obtaining baseline and test evap flow measurements in the absence of a refueling event, is shown. It may be understood that the baseline evap flow measurements and the test evap flow measurements discussed in relation to  FIG. 18  are referred to by the same nomenclature as those discussed at  FIGS. 15-17 , but are slightly different in nature, as will be evident below. Briefly, it may be understood that the baseline evap flow measurements and test evap flow measurements discussed at  FIGS. 18-20  are obtained in the absence of refueling, are conducted with a pump (e.g.  295 ), and involve evacuating the evaporative emissions system with the fuel system sealed and the CPV (and purge pump bypass valve, where included) open. As per the methodology of  FIGS. 15-16 , mass air flow in the intake may be used as a readout as to whether there are restrictions in the evaporative emissions system, for example a CPV (or purge pump bypass valve, where included) that is not fully opening or is sticking closed, canister internal filter being clogged/plugged, canister restriction, a source of undesired evaporative emissions, etc. 
     Method  1800  will be described with reference to the systems described herein and shown in  FIGS. 1-4 , though it will be appreciated that similar methods may be applied to other systems without departing from the scope of this disclosure. Instructions for carrying out method  1800  and the rest of the methods included herein may be executed by a controller, such as controller  212  of  FIG. 2 , based on instructions stored in non-transitory memory, and in conjunction with signals received from sensors of the engine system, such as temperature sensors, pressure sensors, and other sensors described in  FIGS. 1-4 . The controller may employ actuators such as CPV (e.g.  261 ), purge pump bypass valve (e.g.  299   c ) (where included), ELCM (e.g.  295 ), ELCM COV (e.g.  315 ), etc., according to the methods described herein. 
     Method  1800  begins at  1805 , and may include during engine-off conditions where a refueling event is not in progress, conducting a baseline evap flow diagnostic responsive to conditions being met for doing so. In one example, an engine-off condition may include the vehicle having been turned off and where a controller is kept alive to conduct the diagnostic. In another example, the controller may be slept at a key-off event and the controller may be awoken at a scheduled time during the key-off event to conduct the diagnostic. In still another example, an engine-off condition may include a start/stop event where the engine is stopped from combusting air and fuel. 
     Conditions being met for conducting the baseline evap flow diagnostic may include an indication of a clean canister, or in other words, an indication that the canister loading state is less than a threshold (e.g. less than 5% loaded, or less than 1% loaded). Conditions being met may include an indication of no restriction in the canister internal filter, a CPV that is not degraded, a purge pump bypass valve (where included) that is not degraded, a throttle that is functioning as desired, no sources of undesired evaporative emissions stemming from the evaporative emissions system, etc. 
     The baseline evap flow diagnostic may include parking the engine with at least intake valves (and exhaust valves in some examples) closed, for example via rotating the engine via the motor (e.g.  120 ) and controlling intake/exhaust valves to closed positions via actuators (e.g.  483 ,  484 ). The baseline evap flow diagnostic may further include commanding fully open the throttle, commanding fully open the CPV, commanding fully open the purge pump bypass valve (where included), commanding or maintaining the FTIV closed, commanding the ELCM COV to the second position (see for example  FIG. 3B ), and activating the ELCM pump in vacuum-mode to evacuate the evaporative emissions system. The ELCM may be activated at a predetermined speed for the diagnostic. With the ELCM activated, fluid flow in the intake may be monitored via the MAF sensor. Measurements may be obtained via the MAF sensor every 1 second, every 5 seconds, etc. Fluid flow may be monitored for a predetermined duration, after which the MAF measurements may be averaged or otherwise processed to obtain baseline evap flow measurements. After obtaining the baseline evap flow measurements, the ELCM may be deactivated, the ELCM COV may be commanded to the first position, the CPV may be commanded closed, and the throttle may be returned to the position it was in prior to obtaining the baseline evap flow measurement. Furthermore, the intake/exhaust valves may be controlled to appropriate positions for starting the engine for the next engine restart event. 
     Proceeding to  1810 , the baseline evap flow measurements may be stored at the controller. Subsequently, at a later time, at  1815 , method  1800  may include conducting the same procedure in order to obtain test evap flow measurements responsive to conditions being met for doing so. Conditions being met at  1815  may again include a clean canister (e.g. recently purged within a threshold duration of time and/or an indication of a loading state less than a threshold loading state such as less than 5% or less than 1% loaded), but may not include the indications of the absence of CPV degradation, purge pump bypass valve degradation (where included), canister internal filter restriction, canister restriction, etc. Conditions being met may include an indication of a threshold amount of time elapsing since the baseline evap flow diagnostic, or a threshold amount of time elapsing since the last time test evap flow measurements were obtained. 
     Conducting the evap flow test diagnostic may involve the same steps as that discussed above with regard to conducting the baseline flow test diagnostic. It may be understood that the ELCM may be operated at the same speed to obtain the test evap flow measurements, as was utilized to obtain the baseline evap flow measurements. The diagnostic for obtaining the test evap flow measurements may be conducted for the same duration as that for obtaining the baseline evap flow measurements. Proceeding to  1820 , after obtaining the test evap flow measurements, the test evap flow measurements may be stored at the controller. 
     Proceeding to  1825 , method  1800  may include comparing the test evap flow measurements to the baseline evap flow measurements, to indicate a presence or absence of degradation. For example, the controller may compare the baseline evap flow measurements to the test evap flow measurements, and if the test evap flow measurements are not within a threshold of the baseline evap flow measurements, then degradation may be indicated. Otherwise, if the test evap flow measurements are within the threshold of the baseline evap flow measurements, an absence of degradation may be indicated. For example, degradation may be indicated if the test evap flow is less than the baseline evap flow measurements by at least the threshold. Degradation may include a CPV that is not opening as desired, a purge pump bypass valve (where included) that is not opening as desired, a canister internal filter being restricted to at least some extent, a restriction in the canister, etc. After obtaining such results, method  1800  may then end. 
       FIG. 18  thus depicts a high-level example methodology for comparing test evap flow measurements and baseline evap flow measurements to indicate a presence or absence of degradation in the evaporative emissions system. A more detailed methodology is depicted at  FIG. 19 . Accordingly, turning now to  FIG. 19 , an example method  1900  for obtaining the baseline or test evap flow measurements as per  FIG. 18 , is shown. Only one method is illustrated because the methodology for obtaining baseline evap flow measurements is substantially the same as obtaining test evap flow measurements. 
     Method  1900  begins at  1905 , and may include indicating if conditions are met for conducting the baseline or test evap flow diagnostic as discussed at  FIG. 18 . If conditions are not met, method  1900  may proceed to  1910 , and may include maintaining current vehicle operating parameters. Method  1900  may then end. 
     Returning to  1905 , if conditions are met for conducting the baseline or test evap flow diagnostic, method  1900  may proceed to  1915 . At  1915 , method  1900  may include commanding open the CPV, commanding open the purge pump bypass valve (where included) commanding open the throttle, and may further include commanding or maintaining the FTIV closed. While not explicitly illustrated, at  1915 , method  1900  may further include controlling the engine as discussed above with regard to  FIG. 18 , to position at least intake valves closed. Briefly, a motor may rotate the engine unfueled and actuators (e.g.  483 ,  484 ) associated with variable cam timing, for example Ti-VCT, may be utilized to position at least the intake valves closed. 
     Proceeding to  1920 , method  1900  may include commanding the ELCM COV to the second position, and may further include activating the ELCM pump to draw negative pressure on the evaporative emissions system. As discussed above, the ELCM pump may be activated to a predetermined speed. 
     Proceeding to  1925 , method  1900  may include monitoring fluid flow in the intake of the engine, via the MAF sensor (e.g.  202 ). After a predetermined duration of time (e.g. 5 seconds, 10 seconds, 20 seconds, etc.), the MAF measurements may be averaged or otherwise processed, and method  1900  may proceed to  1930  where the measurements (either baseline evap flow measurements or test evap flow measurements) may be stored at the controller. 
     Proceeding to  1935 , method  1900  may include commanding closed the CPV, commanding closed the purge pump bypass valve (where included), commanding the throttle to the position it was in prior to the diagnostic being conducted, and returning engine intake/exhaust valves to the positions they were in prior to conducting the diagnostic, or to positions appropriate for starting the engine for the next engine start request. 
     Proceeding to  1940 , method  1900  may include deactivating the ELCM, and returning the ELCM COV to the first position. With the ELCM deactivated, method  1900  may proceed to  1945 , and may include utilizing the obtained measurements in conjunction with method  1800  depicted at  FIG. 18 , in order to determine the presence or absence of degradation, as discussed above. For example, if method  1900  was conducted to obtain baseline evap flow measurements, then such measurements may be stored at the controller and nothing further may be done. If test evap flow measurements were obtained, then method  1800  may be used to compare the test evap flow measurements to the baseline evap flow measurements, such that the presence or absence of degradation may be indicated. In this way, evaporative emissions system degradation may be indicated without relying on engine combustion. 
     Turning now to  FIG. 20 , an example timeline  2000  for obtaining baseline evap flow and test evap flow measurements in the absence of a refueling event, without the engine combusting and during a key-off event, is shown. In this example timeline  2000 , it may be understood that baseline evap flow measurements have already been obtained, and thus test evap flow diagnostics are obtained. Timeline  2000  includes plot  2005 , indicating whether conditions are met for conducting the evap flow diagnostic, plot  2010 , indicating CPV status, plot  2015 , indicating throttle position, plot  2020 , indicating mass air flow as monitored via the MAF sensor, plot  2025 , indicating FTIV status, plot  2030 , indicating ELCM COV status, plot  2035 , indicating ELCM status, and plot  2040 , indicating a presence or absence of degradation. Each of the above plots are with respect to time. The CPV, throttle, and FTIV may be open or closed, or in the case of the throttle, somewhere between. The ELCM COV may be configured in the first position (see  FIG. 3C ), or the second position (see  FIG. 3B ). There may be no flow ( 0 ) or increased flow (+) as monitored via the MAF sensor. Furthermore, the ELCM may be either off, or may be activated on in a vacuum-mode, where the evaporative emissions system is evacuated. 
     At time t 0 , conditions are not yet met for conducting the test evap flow diagnostic (plot  2005 ). In this example, it may be understood that the vehicle is in a key-off state, and the controller is asleep, and is scheduled to awake at a predetermined time to conduct the test evap flow diagnostic. The CPV is closed (plot  2010 ), the throttle is mostly closed (plot  2015 ), there is no flow in the intake as monitored via the MAF sensor (plot  2020 ), the FTIV is closed (plot  2025 ), the ELCM COV is configured in the first position (plot  2030 ), the ELCM is off (plot  2035 ), and degradation is not indicated (plot  2040 ). 
     At time t 1 , conditions are indicated to be met for conducting the test evap flow diagnostic. In this example, while not explicitly illustrated, it may be understood that the controller is awoken at time t 1  to conduct the test evap flow diagnostic. With conditions being met, at time t 2 , the CPV is commanded fully open, the throttle is commanded fully open, and the ELCM COV is commanded to the second position. While not explicitly illustrated, it may be understood that in some examples, at time t 2 , the engine may be controlled to position at least intake valves in closed configurations, as discussed above. 
     At time t 3 , the ELCM is activated on in vacuum-mode to draw a negative pressure with respect to atmospheric pressure on the evaporative emissions system. Accordingly, between time t 3  and t 4 , mass air flow in the intake increases and stabilizes at a MAF corresponding to the MAF obtained from baseline evap flow measurements obtained previously, represented by dashed line  2021 . In other words, the fluid flow in the intake for the test measurements due to atmospheric air being drawn into the intake, through the open CPV en route to the ELCM is not different than the fluid flow obtained for the baseline measurements. Accordingly, evaporative emissions system degradation is not indicated. In other words, there does not appear to be degradation of the CPV related to the CPV not fully opening or sticking closed, nor substantial clogging/plugging of the canister itself or canister internal filter, nor a presence of undesired evaporative emissions stemming from the evaporative emissions system. If included, such an indication may further indicate the purge pump bypass valve is not degraded. 
     Accordingly, at time t 4 , with the diagnostic having been completed, conditions are no longer met for conducting the diagnostic, the CPV is commanded closed, the throttle is commanded to its initial position prior to the diagnostic, the ELCM COV is commanded to the first position, and the ELCM is commanded off, or is deactivated. With the ELCM COV in the first position, between time t 4  and t 5 , pressure in the evaporative emissions system returns to atmospheric pressure. 
     Thus, a method comprises during a condition where an engine of a vehicle is not combusting air and fuel, applying a pressure from an evaporative emissions system of the vehicle to an intake of the engine, and indicating an absence of degradation in the evaporative emissions system based on a test flow in the intake of the engine being within a predetermined threshold of a baseline flow obtained at an earlier time via applying the pressure. 
     In such a method, a purge valve positioned in a purge line between the fuel vapor storage canister and the engine is commanded fully open, and a throttle positioned in the intake is commanded fully open for obtaining the test flow and the baseline flow. Such a method may further comprise adjusting operation of the purge valve while the engine is combusting air and fuel based at least in part on a presence or the absence of degradation in the evaporative emissions system. 
     In such a method, applying the pressure may includes applying a negative pressure with respect to atmospheric pressure from the evaporative emissions system to the intake. In such a method, a fuel vapor storage canister positioned in the evaporative emissions system is substantially clean of stored fuel vapors. A pump positioned in a vent line of the evaporative emissions system is controlled to a predetermined speed for applying the negative pressure to obtain the test flow and the baseline flow. Furthermore, the method may further comprise sealing a fuel system from the evaporative emissions system for obtaining the baseline flow and the test flow. 
     In such a method, applying the pressure may includes applying a positive pressure with respect to atmospheric pressure from the evaporative emissions system to the intake. Applying the positive pressure may include routing pressure generated during a refueling event of a fuel tank of the vehicle to the intake. 
     In another example, a method comprises with an engine of a vehicle not combusting air and fuel, in a first condition operating an evaporative emissions system in a first mode to obtain a first test flow in an intake of the engine and indicating an absence of degradation of the evaporative emissions system in response to the first test flow being within a first threshold of a first baseline flow obtained at an earlier time via operating the evaporative emissions system in the first mode; and in a second condition, operating the evaporative emissions system in a second mode to obtain a second test flow in the intake of the engine and indicating the absence of degradation of the evaporative emissions system in response to the second test flow being within a second threshold of a second baseline flow obtained at an earlier time via operating the evaporative emissions system in the second mode. 
     In such a method, the first condition includes an indication that a refueling event is not in progress, and wherein the second condition includes an indication that a refueling event is in progress. 
     In such a method, a pressure-build from the refueling event in the second condition routes fluid flow to the intake of the engine, and wherein the second condition includes an indication of a predetermined fuel fill rate of a fuel tank. 
     In such a method, the second condition includes an absence of premature shutoffs of a refueling dispenser during the refueling event. 
     In such a method, operating the evaporative emissions system in the first mode and operating the evaporative emissions system in the second mode in both the first condition and the second condition, respectively, include commanding fully open a canister purge valve positioned in a purge line downstream of a fuel vapor storage canister, commanding fully open a throttle position in the intake, and controlling intake valves of the engine to substantially closed positions. 
     In such a method, operating the evaporative emissions system in the first mode in the first condition includes operation of a pump positioned in the evaporative emissions system, to draw a vacuum on the evaporative emissions system. 
     In such a method, the first condition includes an indication that a fuel vapor storage canister positioned in the evaporative emissions system is substantially free from stored fuel vapor, and where operating the evaporative emissions system in the first mode includes sealing the fuel system from the evaporative emissions system, and wherein operating the evaporative emissions system in the second mode includes fluidically coupling the evaporative emissions system to the fuel system. 
     In such a method, the method may further comprise indicating the first test flow, the first baseline flow, the second test flow, and the second baseline flow based on output of a mass air flow sensor positioned in the intake. 
     In this way, one or more flow maps for controlling a duty cycle of a canister purge valve during canister purging events may be periodically updated via onboard methodology, based on a level to which degradation of the canister purge valve and/or other components of the evaporative emissions system (e.g. canister internal filter) are indicated. By updating the one or more flow maps, purging events may be conducted without risk of engine hesitation and/or stall, a loading state of the fuel vapor canister may be accurately indicated during such purging events, and engine operation may be improved as a result. 
     The technical effect is to recognize that onboard methodology may be used to obtain degradation factors which may be used to update the one or more flow maps. Specifically, the technical effect is to recognize that at a particular vacuum applied on the evaporative emissions system, duty cycling the canister purge valve at two rates and measuring two test rates at which pressure in the evaporative emissions system is reduced to a predetermined negative pressure, may be used to obtain a degradation factor when compared to two baseline rates at which pressure in the evaporative emissions system is reduced to the predetermined negative pressure under similar conditions of the particular vacuum and canister purge duty cycle rates. A further technical effect is to recognize that there may be options for obtaining such degradation factors via situations where the engine is combusting air and fuel, or when the engine is not combusting air and fuel. In this way, the one or more flow maps may be updated even in the absence of engine operation, which may be particularly desirable for hybrid electric vehicles with limited engine run time. 
     The systems and methods discussed herein may enable one or more systems and one or more methods. In one example, a method comprises controlling a duty cycle of a purge valve configured to regulate a purge flow from a fuel vapor storage canister to an intake of an engine during a canister purging event based on a degradation factor obtained by comparison of durations at which a predetermined pressure is reached in an evaporative emissions system at multiple purge valve activation levels. In a first example of the method, the method includes wherein the evaporative emissions system is sealed for obtaining the durations at which the predetermined pressure is reached. A second example of the method optionally includes the first example, and further includes wherein the predetermined pressure comprises a negative pressure with respect to atmospheric pressure. A third example of the method optionally includes any one or more or each of the first and second examples, and further includes wherein a fuel system is sealed from the evaporative emissions system for obtaining the durations at which the predetermined pressure is reached. A fourth example of the method optionally includes any one or more or each of the first through third examples, and further includes wherein the comparison of the durations at which the predetermined pressure is reached at multiple purge valve activation levels includes both conditions for which there is an absence of evaporative emissions system degradation and conditions for which there is a presence of evaporative emissions system degradation. A fifth example of the method optionally includes any one or more or each of the first through fourth examples, and further comprises operating a pump positioned downstream of the fuel vapor storage canister to communicate a predetermined vacuum to the evaporative emissions system for obtaining the durations at which the predetermined pressure is reached. A sixth example of the method optionally includes any one or more or each of the first through fifth examples, and further includes wherein the pump comprises the engine. A seventh example of the method optionally includes any one or more or each of the first through sixth examples, and further includes wherein the pump comprises a purge pump positioned in a purge line between the purge valve and the fuel vapor storage canister. An eighth example of the method optionally includes any one or more or each of the first through seventh examples, and further includes wherein the predetermined pressure that is reached is monitored via a pressure sensor positioned in the evaporative emissions system configured to indicate pressure across a reference orifice in the evaporative emissions system. A ninth example of the method optionally includes any one or more or each of the first through eighth examples, and further includes where the multiple purge valve activation levels include two or more different duty cycles of the purge valve. A tenth example of the method optionally includes any one or more or each of the first through ninth examples, and further includes wherein the degradation factor is used to adjust a flow map for controlling the duty cycle of the purge valve during the canister purging event. 
     Another example of a method comprises updating a flow map at a controller of a vehicle based on an onboard diagnostic that compares a set of test rates at which a predetermined vacuum is reached in a sealed evaporative emissions system to a set of baseline rates at which the predetermined vacuum is reached in the sealed evaporative emissions system; and controlling a purge valve positioned between a fuel vapor storage canister and an engine during a purging event where fuel vapors are purged from the fuel vapor storage canister to the engine, based on the updated flow map. In a first example of the method, the method includes wherein the set of baseline rates are obtained under conditions of an absence of degradation of the purge valve and evaporative emissions system; and wherein the test rates are obtained at a time subsequent to obtaining the baseline rates. A second example of the method optionally includes the first example, and further includes wherein the onboard diagnostic includes duty cycling the purge valve at a first rate and then a second rate while predetermined negative pressure with respect to atmosphere is applied on the evaporative emissions system from a position downstream of the fuel vapor storage canister, for obtaining the set of test rates and the set of baseline rates. A third example of the method optionally includes any one or more or each of the first and second examples, and further comprises maintaining the predetermined negative pressure substantially constant when duty cycling the purge valve at the first rate and then the second rate; and where more than one negative pressure is used to obtain the set of test rates and the set of baseline rates by duty cycling the purge valve at the first rate and the second rate. A fourth example of the method optionally includes any one or more or each of the first through third examples, and further includes where a degradation factor is obtained by comparing the set of test rates to the set of baseline rates; and wherein the degradation factor is used to update the flow map at the controller. A fifth example of the method optionally includes any one or more or each of the first through fourth examples, and further includes wherein the flow map is relied upon for controlling the purge valve in response to a requested flow rate of air and fuel vapor from the fuel vapor storage canister to the engine for the purge event. 
     An example of a system for a hybrid vehicle comprises a fuel vapor storage canister positioned in an evaporative emissions system; a canister purge valve positioned in a purge line fluidically coupling the fuel vapor storage canister to an intake of an engine; a pump positioned in a vent line that couples the fuel vapor storage canister to atmosphere, the pump including a changeover valve configurable to a first position and a second position where the vent line is sealed from atmosphere when the changeover valve is configured in the second position, the pump further including a reference orifice and a pressure sensor configured to measure a pressure difference across the reference orifice; a vacuum source downstream of the fuel vapor storage canister for applying a predetermined negative pressure on the evaporative emissions system; and a controller with computer readable instructions stored on non-transitory memory that when executed, cause the controller to: obtain a first baseline rate and a second baseline rate at which pressure in the evaporative emissions system is reduced to a predetermined vacuum level by configuring the changeover valve in the second position to seal the evaporative emissions system and applying the predetermined negative pressure on the evaporative emissions system via the vacuum source while the canister purge valve is duty cycled at a first rate and then a second rate; at a later time, obtain a first test rate and a second test rate at which pressure in the evaporative emissions system is reduced to the predetermined vacuum level by configuring the changeover valve in the second position and applying the negative pressure on the evaporative emissions system via the vacuum source while the canister purge valve is duty cycled at the first rate and then the second rate; compare the first and second test rates with the first and second baseline rates to obtain a degradation factor that is used to update a flow map stored at the controller that is used to control the canister purge valve for purging fuel vapors from the fuel vapor storage canister; and in response to a request to purge the canister, controller the canister purge valve based on the updated flow map. In a first example of the system, the system further comprises a motor configured to rotate the engine unfueled; and wherein the controller stores further instructions to rotate the engine unfueled to provide the vacuum source for applying the predetermined negative pressure on the evaporative emissions system. A second example of the system optionally includes the first example, and further comprises a purge pump positioned between the canister purge valve and the fuel vapor storage canister; and where the controller stores further instructions to operate the purge pump to provide the vacuum source for applying the predetermined negative pressure on the evaporative emissions system. 
     Note that the example control and estimation routines included herein can be used with various engine and/or vehicle system configurations. The control methods and routines disclosed herein may be stored as executable instructions in non-transitory memory and may be carried out by the control system including the controller in combination with the various sensors, actuators, and other engine hardware. The specific routines described herein may represent one or more of any number of processing strategies such as event-driven, interrupt-driven, multi-tasking, multi-threading, and the like. As such, various actions, operations, and/or functions illustrated may be performed in the sequence illustrated, in parallel, or in some cases omitted. Likewise, the order of processing is not necessarily required to achieve the features and advantages of the example embodiments described herein, but is provided for ease of illustration and description. One or more of the illustrated actions, operations and/or functions may be repeatedly performed depending on the particular strategy being used. Further, the described actions, operations and/or functions may graphically represent code to be programmed into non-transitory memory of the computer readable storage medium in the engine control system, where the described actions are carried out by executing the instructions in a system including the various engine hardware components in combination with the electronic controller. 
     It will be appreciated that the configurations and routines disclosed herein are exemplary in nature, and that these specific embodiments are not to be considered in a limiting sense, because numerous variations are possible. For example, the above technology can be applied to V-6, I-4, I-6, V-12, opposed 4, and other engine types. The subject matter of the present disclosure includes all novel and non-obvious combinations and sub-combinations of the various systems and configurations, and other features, functions, and/or properties disclosed herein. 
     The following claims particularly point out certain combinations and sub-combinations regarded as novel and non-obvious. These claims may refer to “an” element or “a first” element or the equivalent thereof. Such claims should be understood to include incorporation of one or more such elements, neither requiring nor excluding two or more such elements. Other combinations and sub-combinations of the disclosed features, functions, elements, and/or properties may be claimed through amendment of the present claims or through presentation of new claims in this or a related application. Such claims, whether broader, narrower, equal, or different in scope to the original claims, also are regarded as included within the subject matter of the present disclosure.