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Fuel pressure leak

This is a discussion on Fuel pressure leak within the LT1 forums, part of the Vehicle Specific category; Finally got my buddy to connect a fuel pressure guage up and it seems my starting woes are do to ...

  1. #1

    Fuel pressure leak

    Finally got my buddy to connect a fuel pressure guage up and it seems my starting woes are do to the fuel pressure dropping like mad. what keeps the pressure in the system, is there a valve somewhere that went bad or do i need a whole new fuel pump?

    key in and turn fuel pump spins up, fuel pressure jumps to 60 then drops to 0, then while cranking it slowly builds up back then finally starts. if i try to start it after it fires right up, but leave it sit for any period of time and the pressures back down to noda.

  2. #2
    Senior Member bigrondownhiller's Avatar
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    The pressure should bleed down when it sits for a while. If it drops after a couple of minutes then there is a problem. Two things that come to mind are a bad gas cap or a leaking injector. When it is hard to start what does it do? Does it crank for a long time and then start or does it start and run rough for a few seconds to a minute?

  3. #3
    it will crank for a second or two before it finally starts.

    pressure drops literally in seconds until it has been started, then its a slow bleed but enough to have to crank it for a good few seconds before it starts.. not sure of how long that takes but even a 5 hour shift is enough at work to have to do the long crank to get it to start

    its like theres no fuel no fuel no fuel BAM fuel, starts fine, runs fine. turn off, start, fine. turn off, leave for awhile, start... no fuel no fuel no fuel start, runs fine.
    Last edited by grandkodiak; 07-14-2009 at 03:27 PM.

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    Senior Member bigrondownhiller's Avatar
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    Possibly the fuel cap then. It is cheap enough to replace. Some mechanics have to machine to test the old one. Is there a smell of fuel anywhere or any signs of leaking anywhere?

  5. #5
    Not that I can see/smell?

  6. #6
    Senior Member 5.0THIS's Avatar
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    Does it maintain adequate pressure while running? Vacuum line on/off of regulator.

  7. #7
    Impounded
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    Sounds like the pump to me IMO.

  8. #8
    Yea runs fine, its just after its been sitting. I bought a new gas cap today, gunna let it sit for awhile and see if that helps, but I thought a bad cap through a code? Ah well... at the advice of a friend I tried turning the key to accessory so the pump would charge, pull the key out, then back to accessory like 2-3 times to get the pump pushing a few times, and it worked, starts right up...

  9. #9
    Senior Member JaycenK's Avatar
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    You should be able to keep line pressure for several minutes after pressurizing the system. if it wont keep pressure of some kind for that time there is pressure bleeding back through the pump or through a faulty fuel pressure regulator. fuel cap only has to do with tank vapor pressure. It's made to keep vapor in the tank and build it to a set psi when it passes it through the vent atop the tank and threw a filter or into the motor.

  10. #10
    Impounded
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    Quote Originally Posted by JaycenK View Post
    You should be able to keep line pressure for several minutes after pressurizing the system. if it wont keep pressure of some kind for that time there is pressure bleeding back through the pump or through a faulty fuel pressure regulator. fuel cap only has to do with tank vapor pressure. It's made to keep vapor in the tank and build it to a set psi when it passes it through the vent atop the tank and threw a filter or into the motor.
    Thats what I was thinking.


    A lot of buicks/chevys have a hot start issue like this when the pump is about to die, the pump bleeds back when it gets warm and when its cool it works fine.

  11. #11
    Senior Member 5.0THIS's Avatar
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    Quote Originally Posted by grandkodiak View Post
    Yea runs fine, its just after its been sitting. I bought a new gas cap today, gunna let it sit for awhile and see if that helps, but I thought a bad cap through a code? Ah well... at the advice of a friend I tried turning the key to accessory so the pump would charge, pull the key out, then back to accessory like 2-3 times to get the pump pushing a few times, and it worked, starts right up...
    Having to turn the pump to accessory a few times for adequate pressure can be a sign of a bad pump. Or as was said above, your regulator may be bad. Have you checked fuel pressure while it is running, with the vacuum line on and off?

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