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Thread: Fuel pump dying briefly, getting closer to solving my issues (automotive issues :) )

  1. #1
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    Default Fuel pump dying briefly, getting closer to solving my issues (automotive issues :) )

    I'm still fartin around trying to solve my periodic engine studdering issue. I have narrowed it down to the pump, as the hesitations coincide with low fuel pressure readings (I attached my fuel pressure guage to the 'inlet' line from the sending unit and watch it when the engine is idling and hesitates). The reading with the engine running is 47-48 psi (a bit low acording to bentley) and it drops way down for a brief moment when the engine sputters and recovers. FWIW, when I actuate the pump with a switch at the relay, I get a solid 51-52 psi (proper opressure according to bentley). So its the pump hesitating, should have done this a long time ago.........ooooops.

    Next, in order to determine whether it was upstream (power supply to pump), I then hooked up my multimeter to the power supply wire at the sending unit and extended the wire so I could watch it while driving. I noticed that the voltage does NOT drop significantly prior to the pump quiting. The voltage only drops slightly from 13.1 V to high 12.XX V just after the sputter, which I'm guessing is attributable to the brief loss of engine speed.

    I suppose my question are:

    Would this be enough evidence to warrant a pump replacement? They're expensive and I'm cheap, its a tough descision

    From my experience, a fuel pump will get cranky and make noise before dying. Since mine isn't noisy at all, could it be wiring beyond the connector at the sending unit? Has anyone else had a similar experience?

    Thanks again,

    Dave M
    Last edited by Dave M; 05-17-2007 at 09:52 PM.

    10/90 Build 525im, 630,000+km, Eibach/Sachs, Engine Rebuild
    *RIP Oskar the DOG *

  2. #2
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    if you got dang librul treehugger canadians.....didn't stop selling marvel mystery oil up there, i'd tell you to put a full litre/quart bottle into a half a tank and see if it still "falls out" so bad--provided that the behavior of your car is pretty regular now.

    i don't see any reason why your car would't work fine all of the time with 45psi....
    "..Torchinski v. Peterson that it is legal to carry a concealed weapon, so long the weapon is totally slick like a huge ass machine gun that you carry under a trench coat, like in the Matrix."


  3. #3
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    The information you've given here leads me to think the wiring and not the pump are at fault Dave. The voltage drop occurs subsequent to the surge and bypassing the relay circuit picks up pressure.
    Corroded connections or ground sound like the culprit.
    I would run a fused and switched circuit directly to the pump and confirm a good ground to see if things clear up.
    "The gas pedal wouldn't go to the floor if it weren't meant to be there"

  4. #4
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    So does the pump hesitate when you activate with a switch at the relay?
    93 525i / 01 330Ci / 98 Camry / 91 Volvo 240 / 99 Jeep GC

  5. #5
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    Quote Originally Posted by Ross
    The information you've given here leads me to think the wiring and not the pump are at fault Dave. The voltage drop occurs subsequent to the surge and bypassing the relay circuit picks up pressure.
    Corroded connections or ground sound like the culprit.
    I would run a fused and switched circuit directly to the pump and confirm a good ground to see if things clear up.
    Not sure if I fully follow, but I'll try. Just to confirm, I am NOT monitoring the voltage while running the pump via a fused circuit (bypassing the relay). However, I have run the pump for short periods via the fused circuit without it 'failing'. I would need to run it longer to confirm whether it chokes. FWIW, I have replaced the fuel pump relay.

    I'll try tomorrow morning as it usually acts up in the morning.

    Dave

    10/90 Build 525im, 630,000+km, Eibach/Sachs, Engine Rebuild
    *RIP Oskar the DOG *

  6. #6
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    Quote Originally Posted by DanDombrowski
    So does the pump hesitate when you activate with a switch at the relay?
    You can see above or, I'll just say.............it hasn't yet, but I'll run it longer tomorrow to find out. What would be the difference between it failing via the switch and it failing via the relay, provided its a brand spankin new relay.

    Thanks,

    Dave

    10/90 Build 525im, 630,000+km, Eibach/Sachs, Engine Rebuild
    *RIP Oskar the DOG *

  7. #7
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    run a wire right from the pump power connection and monitor it for voltage, either the pump gave up the ghost or you have either a bad wire or ground.

    Pumps will go without even making noise, some make noise all the time and like mine, some are completely silent.
    95 E34 530I V2.31
    ===========
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    John F. Kennedy

  8. #8
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    wait a minute... car is supposed to have 14.4V when running... 13.5 minimum to charge battery. Check voltage at relay socket... should be same as you measure on your battery emergency post and ground.

    If for some reason at your pump location you only get 13.1... then I would say your fuel pump relay is bad.

  9. #9
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    car is supposed to have 14.4V when running...
    no-no-no, sir - not always-
    I have a Hella installed, and that one has written on it 14.1 V
    http://img97.imageshack.us/my.php?im...oschalt2op.jpg
    http://img97.imageshack.us/my.php?im...schalt26lz.jpg
    http://img75.imageshack.us/my.php?im...schalt31jg.jpg

    There are regulators for 14.1V and a bit higher like 14.5V

  10. #10
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    Quote Originally Posted by 632 Regal
    run a wire right from the pump power connection and monitor it for voltage, either the pump gave up the ghost or you have either a bad wire or ground.

    Pumps will go without even making noise, some make noise all the time and like mine, some are completely silent.
    This is exactly what I'm doing. The DMM is up front with me so I can monitor it. I leaning toward bad pump myself.

    10/90 Build 525im, 630,000+km, Eibach/Sachs, Engine Rebuild
    *RIP Oskar the DOG *

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