car starting problem HELP ASSSAPP loosing fuel pressure

Discussion in 'Mechanic and Repair' started by grass disaster, Jun 15, 2007.

  1. grass disaster

    grass disaster LawnSite Silver Member
    Posts: 2,582

    1996 cutlass supreme sl

    3.1 liter


    having problems starting, runs good once started.

    hooked up to fuel pressure gage.

    turn key has good pressure when fuel pump activates(goes up to 40). as soon as i hear the fuel pump stop it drops pressure, goes to about 5 - 0 psi.

    why am i loosing pressure?? it has pressure once it starts about 35 psi

    p.s fuel pump was replaced little over 1 year ago
     
  2. Restrorob

    Restrorob LawnSite Fanatic
    Posts: 11,024

    If it pumps 40 lbs. when you turn the key on do you wait for the pump to stop before you turn the key to crank it up ?

    Have you checked for any fuel leaks possibly around the fuel filter or any steel lines ?
     
  3. grass disaster

    grass disaster LawnSite Silver Member
    Posts: 2,582

    i didn't see any leaks

    if i time it right to crank it just before the pump stops it will start, if i try crank it right away or wait 2 sec after it stops pumping it won't start cause it has no pressure.
     
  4. Restrorob

    Restrorob LawnSite Fanatic
    Posts: 11,024

    Does your fuel rails look like these;

    [​IMG]


    If so (my manual only goes to 95) then it may be possible the fuel regulator #7 is acting up, But remember I've been out the biz for some time now and just throwing things.
     
  5. grass disaster

    grass disaster LawnSite Silver Member
    Posts: 2,582

    well here is a picture of it.

    it starts fine when motor it is cold

    i thought i had the fuel regulator replaced but it doesn't look very new??

    grassfuel.JPG
     
  6. Restrorob

    Restrorob LawnSite Fanatic
    Posts: 11,024

    Yeah, It does look like that ones been on there a little while. You may check that plastic line and make sure it's not broken anywhere (out of sight). You may be able to put a short piece of vac. hose on the regulator and suck on it to see if it's holding a vacuum if you don't have a Mighty-Vac tester.

    Also, By the looks of that engine the under side of the body must have rust on it also. I have replaced quite of few rusted brake lines on northern cars, The brake lines and fuel lines are run together under the body. The coils wrapped around the brake lines would transfer the fluid down the line instead of dripping on the floor.

    I'm just saying, Check the fuel line closely for any wet looking areas because it could have a small pin hole and evaporating before showing a puddle on the floor.
     
  7. grass disaster

    grass disaster LawnSite Silver Member
    Posts: 2,582


    but if it's a leak i would think it would have a hard time starting when the motor is hot and cold.
     
  8. Bill Kapaun

    Bill Kapaun LawnSite Senior Member
    Posts: 915

    I can't speak specifically for GM, but-
    Does this FI system have a return line to the tank?
    IF so, there should be a pressure relief valve somewhere in the system that maintains pressure on the fuel rails, but allows excess fuel to recirculate back to the tank. It's probably part of the fuel pressure modulator.
    I would expect your problem to be there.
     
  9. grass disaster

    grass disaster LawnSite Silver Member
    Posts: 2,582


    is fuel pressure modular the same as the fuel regulator?

    what you said would make the most sense i just need to know where or what part does this.
     
  10. Bill Kapaun

    Bill Kapaun LawnSite Senior Member
    Posts: 915

    Yes- I meant to say regulator:eek:

    As I mentioned, I'm not very well versed in what you have. Look where a return line goes back to the tank.
     

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