Abstract: Methods and systems for fuel system leak detection using passive canister vent valves are disclosed. In one example approach, a method comprises generating engine off vacuum or pressure in a fuel system for leak diagnostics, where the pressure and vacuum are held via first and second mechanical relief valves positioned in parallel with one another and without a valve holding current.

Abstract: Methods and systems are provided for depressurizing a fuel tank prior to refueling the fuel tank. One example method includes adjusting a latchable refueling valve to a latched open position to enable vapor flow from the fuel tank to a vapor canister at a first rate, and responsive to fuel tank pressure being higher than a first pressure threshold after a pre-determined duration at the latched open position, modifying the latchable refueling valve to an unlatched open position. The unlatched open position of the latchable refueling valve enables a second flow rate for fuel vapors, the second flow rate higher than the first flow rate at the latched open position.

Abstract: A method, comprising: indicating leakage on a canister side of a fuel system based on a first fuel system pressure following applying a vacuum to the fuel system with a fuel tank isolation valve closed; and indicating leakage on a fuel tank side of the fuel system based on the first fuel system pressure and a second fuel system pressure following applying a vacuum to the fuel system with the fuel tank isolation valve open. In this way, an ELCM with a single reference orifice may be used to perform a leak test with two different thresholds for leak detection. This may allow vehicles currently in production to meet future emissions standards without costly upgrades to the ELCM.

Abstract: A method for purging a fuel vapor canister, comprising: responsive to an indication of vapor slugs, reversing a direction of air flow through the fuel vapor canister while maintaining purge air intake at a vent line inlet. By reversing the direction of air flow through the fuel vapor canister, the vapor slugs may be adsorbed within the fuel vapor canister and may not affect engine operation. In this way, purge operation may be maintained and emissions may be reduced.

Abstract: Methods are provided for reliving excess vacuum from a fuel tank. In response to elevated fuel tank vacuum levels, a canister purge valve is opened to dissipate the vacuum to an engine intake manifold while the engine is not combusting. Alternatively, the purge valve is opened to dissipate the excess vacuum to the intake manifold while the engine is combusting during conditions when the likelihood of air-fuel ratio errors are lower or when any incurred errors are better tolerated.

Abstract: Methods and systems are provided for enhancing purge flow when applying shallow intake manifold vacuum. An alternate purge route that circumvents the more restrictive canister purge valve and directs purge vapors through a branched path via a less restrictive mechanical purge valve is used during low intake manifold vacuum conditions. By enabling higher purge flow rates when manifold vacuum is lower, a more complete canister cleaning is ensured.

Abstract: A method, comprising: purging fuel vapors from a fuel vapor canister and/or a fuel vapor bleed element to an engine intake with air routed through a transmission bellhousing. In this way, purge air may be warmed by heat generated in the transmission bellhousing during engine operation, thereby increasing desorption efficiency and reducing bleed emissions. Further, purge air may be pressurized in the transmission bellhousing to allow purging operations irrespective of intake manifold vacuum.

Abstract: Methods and systems for controlling and reducing current consumption of a vapor blocking valve are disclosed. In one example, current supplied to the vapor blocking valve is adjusted proportionately to fuel tank pressure to compensate for fuel tank pressure acting on the vapor blocking valve. Vapor blocking valve current is adjusted to reduce current consumption.

Abstract: Methods and systems are provided for depressurizing a fuel tank prior to refueling the fuel tank. One example method includes adjusting a latchable refueling valve to a latched open position to enable vapor flow from the fuel tank to a vapor canister at a first rate, and responsive to fuel tank pressure being higher than a first pressure threshold after a pre-determined duration at the latched open position, modifying the latchable refueling valve to an unlatched open position. The unlatched open position of the latchable refueling valve enables a second flow rate for fuel vapors, the second flow rate higher than the first flow rate at the latched open position.

Abstract: Methods and systems are provided for adjusting and diagnosing a position of a fuel tank isolation valve of a fuel system. In one example, a method may include adjusting the fuel tank isolation valve via electrical pulses and tracking a position of the FTIV by counting each of the electrical pulses. When a vacuum is created in the fuel system, the method may include verifying the position of the FTIV based on resulting fuel system pressures.

Abstract: A method for purging a fuel vapor canister, comprising: responsive to an indication of vapor slugs, reversing a direction of air flow through the fuel vapor canister while maintaining purge air intake at a vent line inlet. By reversing the direction of air flow through the fuel vapor canister, the vapor slugs may be adsorbed within the fuel vapor canister and may not affect engine operation. In this way, purge operation may be maintained and emissions may be reduced.

Abstract: A vehicle method for barometric pressure identification, including adjusting engine operation responsive to barometric pressure, the barometric pressure based on a pressure change at a sector of the fuel system when the sector is sealed with the vehicle travelling. The method may utilize a pressure change at the sealed sector of the fuel system, such as a sealed fuel tank, to identify barometric pressure, even with the engine off for extended durations of vehicle travel. As such, in a hybrid-vehicle application, including during hill descents in which the engine is maintained off, barometric pressure can still be updated.

Abstract: A method and system for conducting leak detection in an evaporative emission control system. The method performs a pressure-based leak test at selected intervals. The pressure-based test includes pressurizing the system, using a pump. Then, the system monitors pressure for a selected period. If system pressure falls below a threshold value during the selected period, the system identifies an initial leak. Upon identifying the initial leak, the system substitutes a vacuum-based leak test at each selected interval. The vacuum-based test includes evacuating the system, using the pump. The system then monitors system pressure for a selected period. If system pressure rises above a threshold value during the selected period, then the system identifies a subsequent leak. Upon receiving notification that the initial leak has been repaired, the system returns to pressure-based leak testing. Where a single pump is used, that pump is configured both for system pressurization and evacuation.

Abstract: Methods are provided for reliving excess vacuum from a fuel tank. In response to elevated fuel tank vacuum levels, a canister purge valve is opened to dissipate the vacuum to an engine intake manifold while the engine is not combusting. Alternatively, the purge valve is opened to dissipate the excess vacuum to the intake manifold while the engine is combusting during conditions when the likelihood of air-fuel ratio errors are lower or when any incurred errors are better tolerated.

Abstract: Methods and systems are described for depressurizing a fuel tank prior to refueling. In one example, before refueling the fuel tank having a pressure above a first predetermined pressure, the pressure may be released through a first valve to the first predetermined pressure and the first valve may be closed. Further, a second valve may be opened to further reduce the pressure to a second predetermined pressure, and if flow through the second valve is less than desired, then the first valve may be opened until the second predetermined pressure is reached.

Abstract: Methods and systems for passively purging a hydrocarbon trap in an engine intake in a vehicle are disclosed. In one example approach, a method comprises, in response to an ambient temperature decrease during an engine off condition while a fuel tank is sealed from atmosphere, delivering fuel stored in a hydrocarbon trap in an intake of the engine to a fuel vapor canister coupled to the fuel tank in an emission control system.

Abstract: Methods and systems for cleaning a pressure relieve valve for a fuel tank are disclosed. In one example approach a method for cleaning a pressure relief valve that is normally activated at a preset negative pressure in a fuel system comprises, during a test cycle, reducing fuel system pressure to a predetermined pressure which is higher than the preset pressure, and measuring pressure changes in the fuel system; and when not in the test cycle, periodically reducing the fuel system pressure to a third pressure which is less than said preset pressure.

Abstract: A method for operating a fuel system is disclosed. The method includes sequentially purging fuel vapors from each of a plurality of regions of a canister. Purging a region includes opening an air inlet valve associated with that region and maintaining air inlet valves associated with each other region closed to direct fuel vapors to at least one purge outlet.

Abstract: A method for an engine fuel system comprises, during an engine-off condition, indicating a refueling event based on a rate of change in fuel tank pressure, and aborting a diagnostic leak detection test based on the refueling event indication. Indicating a refueling event further comprises indicating a refueling event based on the rate of change in fuel tank pressure being greater than a first threshold when the canister vent valve is open, and greater than a second threshold when the canister vent valve is closed, the first threshold being less than the second threshold.

Abstract: A vehicle method for barometric pressure identification, including adjusting engine operation responsive to barometric pressure, the barometric pressure based on a pressure change at a sector of the fuel system when the sector is sealed with the vehicle travelling. The method may utilize a pressure change at the sealed sector of the fuel system, such as a sealed fuel tank, to identify barometric pressure, even with the engine off for extended durations of vehicle travel. As such, in a hybrid-vehicle application, including during hill descents in which the engine is maintained off, barometric pressure can still be updated.