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Fuel pressure test...

Discussion in 'Technical Q&A' started by smb1, Nov 15, 2007.

  1. smb1

    smb1 Rookie

    Jan 26, 2007
    40
    Las Vegas
    Full Name:
    Steve
    I have been having trouble restarting my car (84 Euro QV) after sitting for a half hour and up to 2-3 hours after a nice drive. I have read all the threads I can find and just checked my fuel pressure to try and narrow it down.

    cold- quickly up to 40psi
    warm- after about 5 min 56psi
    system- 78psi
    shut the car off and down to 10psi and to 0 in less than 1 min.

    WUR- about 4 1/2 years old. I watched the accumulator for about 5 min while the car ran and not one drop out of the pipe on the back. It does have an internal check valve in the fuel pump so I can't just replace that (just bought one before I knew though). Can't hear any squealing from the injectors and they were just replaced about a year ago.

    Any thoughts, should I just replace the fuel pump and hope it's the check valve? Any other test I can try?

    Thanks,
    Steve
     
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  3. Motob

    Motob Formula 3
    Professional Ferrari Technician

    Nov 11, 2003
    2,184
    Berkeley, CA
    Full Name:
    Brian Brown
    Most likely it's the check valve in the fuel pump. It's possible to have leakage in the fuel distributor, warm-up regulator or accumulator, but you have already tested the accumulator and the other two are highly unlikely to have leakage.

    The internal check valve in the pump can be removed and inspected/replaced (if you could get the part). It should just screw into the end of the pump. If you look into the outlet of the pump, you should see the white plastic valve. You can take some small needle nose pliers and unscrew the valve from the end of the pump.

    The Bosch pump is relatively cheap. Just take down the Bosch numbers from the outside and source it from a Bosch parts supplier.
     
  4. VR4

    VR4 Karting

    Apr 22, 2004
    58
    vancouver, wa
    Full Name:
    steve


    agreed. its common for check valves in fuel pumps to bleed off fuel pressure. i replace about 4/month at work on fords.
     
  5. spiderseeker

    spiderseeker Formula 3

    Jul 22, 2005
    1,708
    Colorado
    Full Name:
    Steve
    I think it's the accumulator's job to hold pressure after engine shutoff, for a minimum of about 15 minutes.
     
  6. VR4

    VR4 Karting

    Apr 22, 2004
    58
    vancouver, wa
    Full Name:
    steve
    something tells me i have a large amount of research to do...
     
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  8. Motob

    Motob Formula 3
    Professional Ferrari Technician

    Nov 11, 2003
    2,184
    Berkeley, CA
    Full Name:
    Brian Brown
    The accumulator is just a diaphragm with a spring behind it. It acts as a pressure reservoir when the fuel pump is shut off. If there is leakage elsewhere in the system (fuel pump check valve), the pressure in the accumulator will be exhausted,and the system pressure drops to zero.
     
  9. RGigante

    RGigante F1 Rookie
    Project Master Owner

    Nov 1, 2006
    2,874
    Portugal
    For your reference, in case you don't have them:

    fuel accumulator - 0 438 170 004
    fuel pump - 0 580 254 947
    Fuel Pump Non Return Valve - 1 587 010 532

    Bosch references, of course.

    I have recenty replaced the accumulator and the non-return valve on my 328. It was easier to remove them both together and work on the bench.
    If you didn't, take the opportunity to replace the fuel lines from tank to pump and from accumulator to filter. Peace of mind !
     
  10. Verell

    Verell F1 Veteran
    Consultant Owner

    May 5, 2001
    7,001
    Groton, MA
    Full Name:
    Verell Boaen
    Either the fuel accumulator or the check valve can cause those symptoms.

    From your profile you've got a Euro QV. Look at the nipple on the accumulator's back end just after shut-down to see if there's a very very slow gas dripping from it. (A US or CH spec car will have a vapor recovery line on the nipple.) If there's a drip (or gas in the recovery line for US or CH spec cars) then the accumulator's bad (has a leak in the pressure retaining diaphram).

    The check valve's already been discussed.

    BTW, search is your friend, this has been posted half a dozen times in Tech Q&A.
     
  11. jwise

    jwise Formula Junior

    Apr 2, 2003
    781
    Portland Maine
    Verell- the original poster of this thread (Steve) bought my 308. I can't remeber the figures we got during our fuel pressure test last winter- do you remember? I know we never got the pressure to drop to 0 after shutting off the car! I also remember we found two leaking injectors, but I replaced them after the test- so that's not an issue here.

    It's not the accumulator- he said he watched it for quite a while as the car was running.

    Steve- I would also lean towards the valve in the fuel pump. It's really the only thing left that could cause this.
    It should hold a much higher pressure than 10 psi after shut-down.

    I hate blindly replacing expensive parts as much as the next guy- buy what else could it be?

    Good luck- and please keep us updated.

    John
     
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  13. Motob

    Motob Formula 3
    Professional Ferrari Technician

    Nov 11, 2003
    2,184
    Berkeley, CA
    Full Name:
    Brian Brown
    If you wanted to know for sure, you could pinch off the rubber inlet hose to the pump immediately after shutting off the pump to see if the pressure loss changes.
     
  14. smb1

    smb1 Rookie

    Jan 26, 2007
    40
    Las Vegas
    Full Name:
    Steve
    I searched as many threads as I could find and it seems to be one of the last things on the list. I'll get some work done this weekend (I hope) and see if I can replace the check valve as Brian suggested. If not, I've seen a pump for $220 and hopefully that will do it.

    John- as long as I'm in there how old is the fuel filter and fuel lines? Should I just replace cuz I'm there?

    Thank for everyone's input. It makes working on my car much less intimidating. Hopefully someday I can have some useful input.

    Steve
     
  15. smb1

    smb1 Rookie

    Jan 26, 2007
    40
    Las Vegas
    Full Name:
    Steve
    BTW does anyone know where to get the copper washers that go between that banjo fitting from the fuel line and the WUR? It says to replace after checking pressure. Is that correct?
     
  16. spiderseeker

    spiderseeker Formula 3

    Jul 22, 2005
    1,708
    Colorado
    Full Name:
    Steve
    Yes, always replace the copper crush washers. I think I bought mine at Napa when I did the test.
    Bring the old one and match it up.
     
  17. jwise

    jwise Formula Junior

    Apr 2, 2003
    781
    Portland Maine
    Fuel filter is three years old- maybe 5000 miles. I also replaced the braided fuel lines at the same time from the right tank to the hard lines.
    Also- I replaced two the tank breather lines (green/clear Cavis lines) that connect the top of the tanks to each other (I ran out of material so didn't do all three), and the big filler hose to the left tank. I never replaced any of the bottom lines between the tanks, or skinny black injector lines. I'd look at these and decide if replacement is required.


    I would look around Las Vegas for a fastener supply company to source those copper washers. Cheap enough to replace any you remove.
     
  18. Verell

    Verell F1 Veteran
    Consultant Owner

    May 5, 2001
    7,001
    Groton, MA
    Full Name:
    Verell Boaen
    Steve,
    Didn't recognize you as having John's car. Can't recall numbers we measured, but pressure only dropped a neglagable amount during the test interval. Given no dripping w/engine running, I too suspect the fuel pump check valve.

    Umm, did you verify that it's got spark when having starting troubles?
     

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