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Is a noisy fuel pump indicative of a dying fuel pump? 700

posted by  someone claiming to be Justin on  Thu Apr 11 12:19 CST 2002 [RELATED]

Hi,

Hi I have a 740 the fuel pump is functioning rather loudly. I was just wondering if this is usually indicative of a fuel pump on its last legs.
thanks for any responses.
BTW the idle RPM seems low it is at about 650 and the engine has a slight shake to it, what is normal idle RPM for 89 740 gl?








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    Is a noisy fuel pump indicative of a dying fuel pump? 700

    posted by  someone claiming to be Rookie Brickie on  Sat Apr 13 17:08 CST 2002 [RELATED]

    Hi
    I've seen where the main pump's rubber mounts have become dislodged, making the pump sit on the metal bracket, and sounding very loud. Just check it out and see!!








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    Is a noisy fuel pump indicative of a dying fuel pump? 700

    posted by  wichahadaturbo on  Fri Apr 12 19:18 CST 2002
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    I have an 86' 740 GLE I had a really loud weezing noise coming from the fuel pump (which was farely new at the time of the problem), my fuel guage was also broken at the time - next thing i did was check the intank pump, bingo!
    after pulling it out i discovered it was dead, no power at all. The intank pump was putting too much strain on the fuel pump, causing all that racket.
    Your fuel pump might just be old and needs to be replaced, might be a hole in the main feed line of the intank pump - causing it to suck air to the fuel pump, or you might need a new intank pump.







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    Is a noisy fuel pump indicative of a dying fuel pump? 700

    posted by  Neal Wilcer on  Fri Apr 12 01:52 CST 2002
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    It can also be a faulty fuel pressure regulator. Sometimes the failure mode for the fpr is such that there is too much fuel pressure because the fuel return to the tank isn't functioning properly.It can be greater than 90 psi. This results in the fuel pump whining while trying to keep up the pressure.







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    Is a noisy fuel pump indicative of a dying fuel pump? 700

    posted by  someone claiming to be Ivan on  Fri Apr 12 00:45 CST 2002 [RELATED]

    No, it is not.
    Volvos & Saabs are known to have "musical" fuel pumps.
    The ones that are failing are normally detectable at higher speeds
    when fuel starved engines will start to sputter.







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    Is a noisy fuel pump indicative of a dying fuel pump? 700

    posted by  someone claiming to be David Hunter on  Thu Apr 11 12:39 CST 2002 [RELATED]

    I am changing my main fuel pump tomorrow on my 88 740. It had been noisy for a few weeks. This morning when it was a no start because main pump would not run. Jumper applied to the fuel pump relay resulted a strange single kathump sound from the pump.
    Idle speed should be 750 (900 when AC is turned on). Not adjustable as it is controlled by the ECU through the idle air control motor. When idling at 750 and if vibration or shaking is felt on an otherwise smooth idle this may mean that the hydralic motor mounts are collapsed and need tobe replaced.








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      Is a noisy fuel pump indicative of a dying fuel pump? 700

      posted by  someone claiming to be Justin on  Thu Apr 11 13:01 CST 2002 [RELATED]

      Hi,

      Just did some reading and found out a lot of the time a noisy fuel pump is indicative of a failed in tank prepump. So I did a simple test; I took out the intake fuel pump's fuse and the car should have dropped in RPM's a bit due to the in tank pump not sending gas to the main pump, but nothing happened. The car continued to run low RPM's and the Main fuel pump continued to be noisy. so I am thinking that the intank Pump is shot, and the main is good, just noisy because it has to pull gas further and through a dead pump.

      this looks like a pretty easy repair in the Haynes manual, the part is 80 bucks though.








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        Is a noisy fuel pump indicative of a dying fuel pump? 700

        posted by  someone claiming to be Earl on  Fri Apr 12 00:48 CST 2002 [RELATED]

        You're right but the pre-pump can be tested simply. Remove the fuel line from the tank and crank the engine, being VERY carefull that it's draining into a container and no heat, sparks exist nearby. If the tank pump is good, you'll see gas flowing. Before doing that, be sure the in-tank fuse is good and that you have 12v at the connector to the tanks sending unit (w pump). I've seen many a good main pump replaced due to faulty in tank pumps (or the rubber hose to it sucking air, inside the tank as they can split). Bad main pumps are rare.








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          Is a noisy fuel pump indicative of a dying fuel pump? 700

          posted by  someone claiming to be Ivan the "terrible" on  Mon Apr 15 00:45 CST 2002 [RELATED]

          "If the tank pump is good, you'll see gas flowing..."
          I'm confused. How does this test the pre-pump vs. main pump ???
          If the fuel is being pumped out, even with dead pre-pump, it will
          flow fine, if the main pump is O.K.
          Please clarfy for us, mentally challenged...






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