Systems and methods for detection and mitigation of liquid fuel carryover in an evaporative emissions system

1. A method for a fuel system, comprising:

during a first condition, activating a vacuum pump 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 the threshold, maintaining the vacuum pump on until a fuel tank pressure decreases to atmospheric pressure.

2. The method of claim 1 , wherein the first condition includes a fuel tank isolation valve in an open conformation.

3. The method of claim 2 , wherein the fuel tank isolation valve was opened prior to a recently completed refueling event.

4. The method of claim 3 , further comprising:

responsive to the second fuel tank pressure decay rate being greater than the threshold, determining whether the recently completed refueling event included an automatic shutoff of a refueling dispenser; and

responsive to determining that the recently completed refueling event did not include an automatic shutoff of a refueling dispenser, indicating to perform one or more on-board tests to determine an integrity of the fuel system.

5. The method of claim 4 , further comprising:

responsive to determining that the recently completed refueling event did include an automatic shutoff of a refueling dispenser, determining whether a fuel level indicator indicates that a fuel tank is full; and

responsive to determining that the fuel level indicator indicates that the fuel tank is full, indicating that the fuel tank was overfilled.

6. The method of claim 5 , further comprising:

responsive to determining that the fuel level indicator indicates that the fuel tank is not full, indicating an on-board test to determine an integrity of the fuel level indicator.

7. The method of claim 1 , further comprising:

responsive to the second fuel tank pressure decay rate being less than the threshold, deactivating the vacuum pump; and

indicating a restriction in an evaporative emissions system coupled to the fuel system.

8. The method of claim 7 , further comprising:

responsive to indicating the restriction in the evaporative emissions system, suspending a canister purge operation at a subsequent engine-on event.

9. A method for a fuel system, comprising:

following a refueling event, monitoring a fuel tank pressure bleed-down rate;

indicating a presence of liquid fuel in an evap recovery line responsive to a first fuel tank pressure bleed-down rate less than a threshold;

actively returning the liquid fuel in the evap recovery line to a fuel tank; and

responsive to the first fuel tank pressure bleed-down rate being greater than the threshold, sealing the fuel tank responsive to a fuel tank pressure decreasing to atmospheric pressure, and updating a canister purge schedule.

10. The method of claim 9 , wherein actively returning the liquid fuel in the evap recovery line to the fuel tank comprises:

maintaining a fuel tank isolation valve open; and

activating an evaporative leak check module vacuum pump in a pressurizing mode.

11. The method of claim 10 , further comprising:

maintaining the evaporative leak check module vacuum pump on in the pressurizing mode responsive to a second fuel tank pressure bleed-down rate greater than the threshold; and

deactivating the evaporative leak check module vacuum pump responsive to the fuel tank pressure decreasing to atmospheric pressure.

12. The method of claim 11 , further comprising:

closing the fuel tank isolation valve responsive to the fuel tank pressure decreasing to atmospheric pressure.

13. The method of claim 11 , further comprising:

deactivating the evaporative leak check module vacuum pump responsive to the second fuel tank pressure bleed-down rate being less than the threshold; and

indicating a restriction in the evap recovery line.

14. The method of claim 13 , further comprising:

responsive to indicating the restriction in the evap recovery line, suspending a canister purge operation at a subsequent engine-on event.

15. The method of claim 9 , wherein the refueling event comprises one or more automatic shutoffs of a refueling dispenser.

16. The method of claim 9 , further comprising:

monitoring the fuel tank pressure and a fuel tank fill level during the refueling event.

17. A fuel system, comprising:

a fuel tank coupled to a fuel vapor canister via one or more evap recovery lines;

a fuel tank isolation valve coupled between the fuel tank and the fuel vapor canister;

a fuel tank pressure sensor;

a fuel tank fill level sensor;

an evaporative leak check module comprising a reversible vacuum pump coupled between the fuel vapor canister and atmosphere; and

a controller storing instructions in non-transitory memory that, when executed, cause the controller to:

receive a request for a refueling event;

open the fuel tank isolation valve;

monitor a fuel tank pressure via the fuel tank pressure sensor and a fuel tank fill level via the fuel tank fill level sensor for a duration of the refueling event;

indicate liquid fuel carryover into the one or more evap recovery lines responsive to a first fuel tank pressure decay rate following the refueling event being less than a threshold; and

responsive to an indication of liquid fuel carryover into the one or more evap recovery lines, activate the reversible vacuum pump to direct atmospheric air into the fuel system.

18. The fuel system of claim 17 , wherein the controller further stores instructions in non-transitory memory that, when executed, cause the controller to:

maintain the reversible vacuum pump on responsive to a second fuel tank pressure decay rate being greater than the threshold.

19. The fuel system of claim 18 , wherein the controller further stores instructions in non-transitory memory that, when executed, cause the controller to:

indicate a restriction in the one or more evap recovery lines responsive to the second fuel tank pressure decay rate being less than the threshold.