A purge solenoid valve is opened to introduce an atmospheric pressure into a fuel tank, the purge solenoid valve is closed to operate a negative pressure pump, and set an internal pressure of the tank to a reference pressure Pb. Then, a changeover valve is closed, and the purge solenoid valve is opened to cause a canister to communicate with an intake passage. Further, the changeover valve is opened, and the purge solenoid valve is closed. Then, a first tank internal pressure Po is detected and subtracted from the reference pressure Pb. If a calculated first pressure deviation Po is larger than a first threshold P1, it is determined that there is no open sticking in a sealing valve.

Methods and systems are provided for managing fuel vapors in a vehicle fuel system. In one example, a method includes commanding or maintaining closed a vapor blocking valve during a purging operation such that vapor flow is directed from a fuel tank to a fresh air side of a vapor canister via a first restricted vapor line, thereby enabling high purge flow rates and deep vapor canister vacuum while avoiding fuel tank vacuum. In this way, canister purge operation may be made more efficient, thereby reducing hydrocarbon bleed emissions.

A fuel evaporative emission processing system suitable for a hybrid vehicle includes a shut-off valve, a first purge control valve and a second purge control valve. The shut-off valve is selectively opens and closes a fuel vapor passage between a fuel tank and a canister. The first purge control valve selectively opens and closes a purge passage between the canister and the intake passage of an internal combustion engine. The second purge control valve selectively opens and closes a tank opening passage between the canister and the fuel tank. When releasing a pressure for refueling, the second purge control valve with a small diameter opens prior to opening of the shut-off valve so that blow-by of gas associated with opening of the shutoff valve is prevented.

A portable engine-driven system comprising an engine having an air intake passage, a fuel tank operatively coupled to the engine, a valve, and a pressure regulator. The valve may be coupled between the fuel tank and the air intake passage and configured to transition between a first position and a second position. The first position may allow fuel vapor to flow between the fuel tank and the air intake passage and the second position may inhibit the fuel vapor from flowing between the fuel tank and the air intake passage. The pressure regulator may be positioned in line between the fuel tank and the air intake passage.

Methods and systems are provided for detecting and mitigating the presence of liquid fuel carryover in an evap system of a vehicle in response to a refueling event. In one example, during a first condition, a vacuum pump is activated to pressurize the fuel system responsive to a first fuel tank pressure decay rate being less than a threshold, and responsive to a second fuel tank pressure decay rate being greater than a threshold, the vacuum pump is maintained on until a fuel tank pressure decreases to atmospheric pressure. In this way, liquid fuel carryover can be quickly and accurately diagnosed, such that mitigating actions may be taken to ensure liquid fuel is returned to the tank prior to contacting the adsorbent material within the vapor canister.

The disclosure relates to a tank ventilation apparatus for a motor vehicle which has a scavenging line which is arranged between an activated-carbon container and an intake line of the motor vehicle and in which an electrically driven scavenging pump is arranged. Furthermore, an electrically controllable directional control valve is provided in the scavenging line between the activated-carbon container and the electrically driven scavenging pump.