Methods and systems are provided for diagnosing degradation and/or alteration in an evaporative emission control system of a vehicle. In one example, a method may include, during a refueling, monitoring a fuel tank pressure and a fuel fill level, and detecting a presence or an absence of a fuel vapor canister of the EVAP system based on a change in fuel tank pressure with an increase in fuel level.

Methods and systems for diagnosing operation of an evaporative emissions system are described. The methods and systems may include increasing an amount of vacuum stored in an evaporative emissions system during discontinuously operating an engine in a boosted operating mode. Storing vacuum allows the evaporative emissions system to reach a desired vacuum level to verify absence of an evaporative emissions system breech.

A vehicle includes an engine, a fuel tank, a primary canister, a buffer canister, a purge valve, a check valve, and a controller. The fuel tank is configured to store fuel. The primary canister is configured to receive and store evaporated fuel from the fuel tank. The buffer canister is configured to receive and store the evaporated fuel from the fuel tank. The buffer canister is disposed between the primary canister and the engine. The purge valve is disposed between the buffer canister and the engine. The purge valve is configured to direct the evaporated fuel from the primary and buffer canisters to the engine when open. The check valve is disposed between the primary and buffer canisters and is configured to restrict backflow of the evaporated fuel from the buffer canister toward the primary canister. The controller is programmed to diagnose the operability of the check valve.

A system for testing an evaporative emissions (EVAP) canister of a vehicle according to the present disclosure includes an evaporator configured to contain liquid fuel, a fuel vapor supply line configured to deliver a mixture of fuel vapor and carrier gas from the evaporator to the EVAP canister, and a fuel vapor supply valve disposed in the fuel vapor supply line. The test system further includes a gas density meter configured to measure a density of the fuel vapor mixture flowing through the fuel vapor supply line, and a valve control module configured to control a position of the fuel vapor supply valve to adjust a flow of fuel vapor from the evaporator to the EVAP canister based on the fuel vapor mixture density.

Methods and systems for determining pressure changes across at least two fuel vapor storage canisters are described. The methods and systems may include determining the pressure changes via a sole pressure sensor. In one example, fuel vapor canister bypass passages are provided to determine pressure values at a plurality of positions within an evaporative emissions system.

A failure diagnosis method and a failure diagnosis system of a dual purge system may determine whether a closed stuck failure or an opened stuck failure occurs in a line forming a dual purge system by measuring a pressure in a negative pressure formation device and comparing the corresponding pressure with a predetermined reference value when a purge valve of the dual purge system is in an opened or closed state, and may determine whether the failure occurs in components related to a secondary purge line in the dual purge system in which it is difficult to determine whether the failure occurs in a conventional failure diagnosis method of a single purge system in a simple method.

Evaporative emission purge control systems and methods use a cost factor to incentivize operation of an internal combustion at torques favorable for purge. An evaporative emission control system is configured to collect fuel vapor. A controller determines whether an operating speed of the internal combustion engine is within a target purge region that is bounded by a lower speed threshold and an upper speed threshold of the internal combustion engine. When the operating speed of the internal combustion engine is within the target purge region, the controller applies a cost factor to operating points for the internal combustion engine, and based on the cost factor, the operating points are set to include an operating torque for the internal combustion engine to generate an intake pressure of the internal combustion engine at a level below atmospheric pressure for a purge of the evaporative emission control system.

Methods and systems for diagnosing operation of an evaporative emissions system are described. The methods and systems may include increasing an amount of vacuum stored in an evaporative emissions system during discontinuously operating an engine in a boosted operating mode. Storing vacuum allows the evaporative emissions system to reach a desired vacuum level to verify absence of an evaporative emissions system breech.

A vehicle includes an engine, a fuel tank, a primary canister, a buffer canister, a purge valve, a check valve, and a controller. The fuel tank is configured to store fuel. The primary canister is configured to receive and store evaporated fuel from the fuel tank. The buffer canister is configured to receive and store the evaporated fuel from the fuel tank. The buffer canister is disposed between the primary canister and the engine. The purge valve is disposed between the buffer canister and the engine. The purge valve is configured to direct the evaporated fuel from the primary and buffer canisters to the engine when open. The check valve is disposed between the primary and buffer canisters and is configured to restrict backflow of the evaporated fuel from the buffer canister toward the primary canister. The controller is programmed to diagnose the operability of the check valve.

Methods and systems for diagnosing operation of an evaporative emissions system are described. The methods and systems may include increasing an amount of vacuum stored in an evaporative emissions system during discontinuously operating an engine in a boosted operating mode. Storing vacuum allows the evaporative emissions system to reach a desired vacuum level to verify absence of an evaporative emissions system breech.