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Thread: Gas cap hissing

  1. #1
    Join Date
    Aug 2007
    Location
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    My Cars
    1972 3.0 CSi-1988 M6

    Gas cap hissing

    There has always been a fair amount of hissing when my coupe’s gas cap is removed. Just changed the fuel pump with an oe BMW unit and the hiss is completely gone. What changed?
    Bert
    91 850i-A
    1972 3.5 CSi (L-jet, Getrag 265 5 speed)
    1988 ///M6
    2021 X3 M40i

    The back to back BIG COUPE” duo

  2. #2
    Join Date
    Feb 2010
    Location
    Hampshire UK
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    99 840ci Sport Indv
    As changing the pump should have no affect on tank vacuum - I would guess that the rubber ring has not been installed correctly:

    http://www.realoem.com/bmw/enUS/show...22#16111179637
    Timm..2007 E64 650i Individual Sport..1999 E31 840ci Individual Sport..ex owner of 2000 E38 740..1999 E38 740i V8 M62..1998 E38 735i V8..1993 E32 730i V8..1988 E28 518i


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  3. #3
    Join Date
    Aug 2007
    Location
    San Francisco, CA
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    1,570
    My Cars
    1972 3.0 CSi-1988 M6
    So what is the norm, a certain amount of vacuum hissing or none at all? As for the rubber seal installation, I made sure the seal was seated properly, then the plastic lock collar was tightened to spec.
    Bert
    91 850i-A
    1972 3.5 CSi (L-jet, Getrag 265 5 speed)
    1988 ///M6
    2021 X3 M40i

    The back to back BIG COUPE” duo

  4. #4
    Join Date
    Aug 2007
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    Posts
    1,570
    My Cars
    1972 3.0 CSi-1988 M6
    The swoosh is back. Tightened the lock collar a little more, guess it was not torqued adequately. Used another better quality torque wrench and tightened to 41 lbs.
    Bert
    91 850i-A
    1972 3.5 CSi (L-jet, Getrag 265 5 speed)
    1988 ///M6
    2021 X3 M40i

    The back to back BIG COUPE” duo

  5. #5
    Join Date
    Jan 2005
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    54,654
    My Cars
    11/88 E32 750iL+98 E36M3
    are the fuel tank breather valves connected? Check the hoses from throttle valves to charcoal filter, especially the plastic distribution piece #14, that often breaks, http://www.realoem.com/bmw/enUS/show...diagId=13_0354
    If the valve is working properly, it is sprung closed and powered open. quick test of fuel tank breather valve: The fuel tank breather valve should have a resistance of 45 ohms ± 20 and be closed in de-energized state.
    Shogun tricks and tips for the E32 series are HERE!

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