System and methods for evaporative emissions leak testing

摘要

A method for a fuel system is provided, comprising: during a first engine-off condition, coupling a fuel tank to a fuel vapor canister, and indicating degradation based on a change in pressure at the fuel vapor canister, and during a second engine-off condition, coupling the fuel vapor canister to an intake of an engine, and indicating degradation based on a change in pressure at the fuel vapor canister. The first engine-off condition may include an absolute fuel tank pressure greater than a threshold, while the second engine-off condition may include an engine spinning unfueled. In this way, a vacuum or pressure may be applied to the fuel vapor canister during an engine-off condition without requiring a dedicated vacuum pump coupled to the fuel vapor canister.

主权项

1. A method, comprising:
during an engine-off event:
in a first condition, including a fuel tank absolute pressure greater than a threshold where a fuel tank is isolated from a fuel vapor canister, coupling the fuel tank to the fuel vapor canister while sealing the canister and fuel tank from an engine intake manifold and atmosphere, and indicating degradation based on a first change in pressure at the fuel vapor canister; andin a second condition, if fuel tank absolute pressure is less than the threshold where the fuel tank is isolated from the fuel vapor canister, coupling the fuel vapor canister to an engine intake while maintaining the fuel tank sealed from atmosphere and the fuel vapor canister, and indicating degradation based on a second change in pressure at the fuel vapor canister.