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Thread: Fuel Pressure

  1. #1

    Default Fuel Pressure

    So my pump primes up line to the 43 psi where it’s should be, but right after the pump shuts off the pressure drops to zero. Bad injectors of something else?
    Last edited by 5o2slow; 07-16-2019 at 09:31 PM.

  2. #2
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    That's normal operation, it does not have a check valve that will hold pressure.
    Last edited by 81 TransAm; 07-17-2019 at 08:20 AM.

  3. #3

    Default

    No, it’s not normal.

  4. #4
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    Default

    Pumps without non-return valves cause this, but is nothing to be worried out. I'd rather have fuel pressure fall to zero, because then I know I won't have a flooded engine from a weepy injector. Fuel doesn't compress. If you don't like what you have, add a non-return valve after the pump, but it needs to flow better than the pump in the forward direction. Gary
    Last edited by Gaz64; 07-17-2019 at 04:52 AM.
    Regards, Gary

  5. #5

    Default

    Maybe I have written this wrong.
    85 Corvette.
    Turn on ignition pump comes on and primes to the 43.5 psi as it’s supposed too.
    As soon as the pump shuts down after priming the fuel pressure drops back to 0 psi.
    It’s all the stock lines for the exception of the FP regulator.
    It has always maintained 43.5 after the pump primes.
    I know that when you have a leaky injector psi drops some, but my psi drops immediately after the pump is done priming.
    That’s not normal. It should maintain the pressure at 43.5.
    The car starts for a second and stalls.
    Thank you for your suggestions.

  6. #6
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    Default

    A better explanation always helps. If you don't have any leaks in any of the fuel lines, then it only has 3 places it can lose pressure through. The FPR, the injectors or the fuel pump.

  7. #7

    Default

    No fuel leaks in lines. Now does the FPR hold the pressure?
    Does the fuel pump hold the pressure in the line once primed?
    Injectors are about 7 yrs old, but don’t have more than 20 minutes run time as the car was sitting for that long.

  8. #8

    Default

    What kind of pump is it? If there's no check valve at the pump, pressure will drop immediately, as it does in your case. Andrew
    IG @projectgattago

  9. #9

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    It’s an in-tank Walbro 340.

  10. #10
    Join Date
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    Default

    The fuel pump will be the cause. Many high performance pumps do not have non-return valves, since they can limit horsepower.
    Suggested Add-On
    Quantum Inline High-Flow Viton Fuel Pump Check Valve 8mm - 5/16"
    HFP-FT3

    A common side effect of high volume (& OEM) in-tank fuel pumps are their inability to maintain static fuel pressure when the vehicle sits for any extended period of time. This leads to a "hard starting" condition where the starter must engage continuously for 3-4 seconds (or longer) before the engine will finally start. This side effect is commonplace with all high performance, high volume fuel pumps including Walbro, AEM, Aeromotive, and Quantum fuel pumps. Our check valve resolves this issue once and for all, and can be used either in-tank, or externally. It features a high-flow design which uses Viton seals and stainless steel internals which are compatible with modern pump gasoline as well as E85. This check valve will not significantly alter the flow capabilities of your pump, but it will make sure that the car starts instantly, every single time. We recommend installing an inline check valve even with a brand new pump, so the tank doesn't need to be dropped again a few months later. Gary
    Regards, Gary

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