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Thread: Fuel Pump Settings --> Prime before crank - Power On

  1. #1
    Tuner in Training
    Join Date
    Apr 2013
    Posts
    44

    Fuel Pump Settings --> Prime before crank - Power On

    Good day, everyone. I'm working on a 2020 Roush with a return fuel system. The pumps do not hold pressure when they are off. When I start the car, it builds pressure and will start when it is cold. When the car is hot, it will stall out on the first try, but since the pumps fire up, if I crank it again, it will fire up with no problem.

    Does anyone know of a way to command the pumps to prime when the engine start button is pressed, or any other way to make them "prime" before firing? Or even a way to continuously run the pumps when the power is on? Any ideas would be appreciated.
    Bryan Mundy
    #MundyTuned
    www.mundytuned.com

  2. #2
    Advanced Tuner
    Join Date
    Jun 2020
    Posts
    822
    It sounds like the pumps are missing the check valves that hold pressure on the system when it’s off. This prevents vapor lock on hot starts.

  3. #3
    Tuner in Training
    Join Date
    Apr 2013
    Posts
    44
    Yes, I agree with your statement. I am not the builder of this car, and I am looking for a Band-Aid. Of course, even though I have shown there is no fuel pressure, it's still "in the tune." You know how that goes.
    Bryan Mundy
    #MundyTuned
    www.mundytuned.com

  4. #4
    Advanced Tuner
    Join Date
    Jun 2020
    Posts
    822
    As a workaround you could try starting up on 100% gdi.

  5. #5
    Tuner in Training
    Join Date
    Apr 2013
    Posts
    44
    ^^ YES! Thank you very much, I'll give that a try.
    Bryan Mundy
    #MundyTuned
    www.mundytuned.com

  6. #6
    I have a return fuel system, dual TI pumps and they both have check valves. Pressure will bleed off in about 2 seconds after shutting the car off. Thats normal I am told by Fore. They will not hold pressure for long. They are triggered by the FPDM wire under the seat. This wire is the one that powers the FPDM and comes from a relay under the hood. The primary pump will run as soon as I hit the engine start button. Hope this helps