How long should fuel pressure remain in rail after shut down?

Discussion in 'Gen 1 & 2 - Engine, Exhaust, Drive Line & AC syste' started by jimtash, Sep 24, 2012.

  1. jimtash

    jimtash SHO Member

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    Mine drops off almost immediately and if I press the valve at the rail in, the fuel coming out is not under a lot of pressure. Instead of shooting out, it flows out and I hear air bubbles along with it. Pump was replaced last year.

    Trying to diagnose an intake backfire. Also when I replaced the fuel filter after 10 minutes of the car being off, there was no no pressure or gas in the line running after the filter at all.
     
    Last edited: Sep 24, 2012
  2. kevinspann

    kevinspann 87 Octane

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    Days/months. Sounds like a bad check valve in the pump...
     
  3. jimtash

    jimtash SHO Member

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    Yeah something is amiss. It does prime but pressure and flow immediately drop off as well if it's not started.

    Thanks.
     
  4. 93markVIII

    93markVIII SHO Member

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    yes. should hold pressure quite a long time.
    bad check valve in the pump is a somewhat common issue.
     
  5. JRA2000TL

    JRA2000TL The Complainer

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    Did you put an airtex pump in there?
     
  6. Ishodu

    Ishodu Administrator Staff Member

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    It won't be causing your issue. Those of us with after market regulators have no pressure after shut down every time.
    The only thing you might get from low rail pressure after shutting car off is vapor in there from boiling fuel. This can cause a hard start.
     
  7. jimtash

    jimtash SHO Member

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    I think it's a Bosch pump. Got it at Rockauto on a closeout deal.

    Haven't tested the pressure itself but would a low PSI cause a fuel starvation problem?

    Have also experienced long cranking hard starts, a gas smell, and a low throttle tip in hesitation under load.
     
    Last edited: Sep 24, 2012
  8. SHOtime2511

    SHOtime2511 CGP

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    Any codes?
     
  9. jimtash

    jimtash SHO Member

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    This is all related to the intake popping at idle and I'm at my wits end with trying to figure it out. Swapping out between two PCMs, one a LOS and the other an X2J, the LOS shows nothing but the X2J will show a 157. Low throttle tip in hesitation has been present for a while now even before the intake popping noise started. Car seems to idle better with the MAF unplugged but the popping noise is still present.

    Every time it pops now, I also get a slight ping or knock. That just started up recently When everything was running correct, the plugs had a nice tan color to them and now they look pure white which is a sure sign of running lean. No vacuum leaks and the only other thing left is fuel. I just know on my V-8 that in order to relieve the fuel pressure, I have to pull the fuse to pump in order to burn it all out of the rail. Pressing the valve down produces such a continuous spray of pressurized fuel that doesn't subside even after sitting for an hour. On the V-6, it'll just flow out like running out of a tap with hardly any pressure behind it.
     
  10. 93markVIII

    93markVIII SHO Member

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    so bad pump or clogged in-tank filter.

    you need to test fuel pressure with the car running.

    if you unplugged the MAF with the car running, that will give you a 157 code.
     
  11. jimtash

    jimtash SHO Member

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    Code 157 seems to be legit. Verified by disconnecting battery to clear codes, reconnecting and letting the car idle til cooling fan comes on with MAF connected. Then do a KOEO test and it always pops up.
     
  12. 93markVIII

    93markVIII SHO Member

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    ok. tried another MAF?

    when you reset the computer, does the car run ok and seem to get worse as it warms up? if so, then the maf is screwing with the fuel tables.
    either bad maf, or bad wiring?

    reset the computer and leave the maf unplugged. then it wont use the maf. see what it does.
     
  13. jimtash

    jimtash SHO Member

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    Still pops with the MAF unplugged but it idles noticeably smoother. Does that with both PCMs even though the LOS doesn't throw a code (which would be a 66) and the X2J does. X2J also runs slightly different than the LOS due to the hotter tune. That's why I'm looking at the pump now. Everything else has been ruled out. MAF wiring is OK and checks out good with a volt meter. The signal to the PCM from it fluctuates even though it's just idling from .05 to .06 volts. The car is down on power as well. Definitely missing its pep.

    One other thing is the engine blew out two plugs at the same time yesterday when diagnosing. And by that I mean the insulators spun freely inside the body causing a huge air leakage. Cylinders 1 and 5 to be exact.
     
    Last edited: Sep 25, 2012
  14. SHOtimer

    SHOtimer #2910

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    What is your fuel psi when the car is running? You get an improvement when you pull the vacuum tube off of the fuel pressure regulator?

    Doug
     
  15. 93markVIII

    93markVIII SHO Member

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    yeah, back to pump. check that pressure.
     
  16. jimtash

    jimtash SHO Member

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    Definitely think it's the pump. Went to start car, turned the key on and checked to see if there was fuel in the rail. None. Cycled key on and off 3 times, pump sounds like it's priming but there's no gas in the rail. Did get a faint sound of air coming out of it.
     
  17. JRA2000TL

    JRA2000TL The Complainer

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    You can't get a break with that car it seems. So, when you replace the pump, are you going to drop the tank or do the access hole modification under the seat? I'm leery to cut into the sheet metal of my car but I hear folks do it all the time. Takes alot less time to replace the pump that way---even watched frosho change his out in the parking lot at the Charlotte convention last year.
     
  18. jimtash

    jimtash SHO Member

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    Man you ain't kidding. Hopefully this will be it.

    I already modded mine last year when I installed the current pump in it. It's harder to pull the seat cushion out than it. No way in hell I'm dropping the tank. It's an easy mod and one that will not harm the structure of the car as far as I'm concerned. If you do yours too, go back and repaint where you cut and use 3M strip caulk this to seal the area.
     
    Last edited: Sep 25, 2012
  19. jimtash

    jimtash SHO Member

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    Didn't put the pump in yet but the Delphi FEO155 pump at Rockauto is actually the Walbro 526 pump. $40.00 and you can't beat it.
     
  20. jimtash

    jimtash SHO Member

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    OK pump is in. For some reason it wouldn't prime and had a horrible sound to it so back out it came. Put battery voltage to it while submerging it in water and now it works. Sounds normal and functions fine. The old pump BTW was missing the strainer and it was laying at the bottom of the tank. Car runs fine, doesn't miss out the back or backfire into the intake but fuel pressure is still not holding after shutdown.

    Edited to add luckily the floor pan mod was done and the pump was easy to get to. Imagine having to go back and drop the tank again. Highly recommend it.
     
    Last edited: Oct 3, 2012

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