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Thread: Humming sound just after ignition is switched on

  1. #1
    Join Date
    Aug 2005
    Posts
    593

    Default Humming sound just after ignition is switched on

    Car started making a humming sound, as if something is grinding against something else, just after the ignition is switched one. This lasts for only a couple of seconds then stops. Pump is already noisy, but this sound seems to come from under the front hood. You can actually feel it, not just hear. Sometimes this also happens when the engine is running. It could be happening more frequently, but while driving you won't hear it.
    1994 520i with M50 engine, manual transmission and air conditioner.
    VIN: GG45422

  2. #2
    Join Date
    Dec 2003
    Location
    Eastern Tennessee USi
    Posts
    14,788

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    aux pump pulsating and transmiting vibrations to the front??
    95 E34 530I V2.37
    ===========
    Those who make peaceful revolution impossible will make violent revolution inevitable.

    John F. Kennedy

  3. #3
    Join Date
    May 2006
    Location
    Antwerp, Belgium
    Posts
    552

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    Or ICV? I get the humming sometimes on 'electrics and ignition on' before I crank. Sometimes also when I tap the throttle over idle and let it fall back to it.
    2008 audi A3 1.9tdi
    (former 1991 520i LPG)

  4. #4
    Join Date
    Aug 2005
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    593

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    Is there an auxiliary fuel pump?
    1994 520i with M50 engine, manual transmission and air conditioner.
    VIN: GG45422

  5. #5
    Join Date
    May 2006
    Location
    Antwerp, Belgium
    Posts
    552

    Default

    Quote Originally Posted by t_marat
    Is there an auxiliary fuel pump?
    Not up front. I remember reading about some BMW models having two fuel pumps but those were in the rear. One for fuel pickup and filtering, the second for pressurising the fuel lines to the engine.

    I'm thinking it could well be the aux water pump even if I had the symptom when blipping from idle. Does it sound like the sound travels from the front-left to the dash and sides?
    2008 audi A3 1.9tdi
    (former 1991 520i LPG)

  6. #6
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    Dec 2003
    Location
    PA
    Posts
    5,403

    Default

    you're definitely hearing the aux water pump

  7. #7
    Join Date
    Aug 2005
    Posts
    593

    Default

    Will an auxiliary water pump ran even if the heater is off, that is temp regulators set to minimum level and blower off?
    1994 520i with M50 engine, manual transmission and air conditioner.
    VIN: GG45422

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