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physed 12/5/2011
2009 Mini Cooper S 7.5L - Engine
Engine makes sound of deflating balloon when shut off
I have a sound coming from the back (near Firewall) of the engine when I turn the car off, which sounds like air escaping from an untied balloon. Any ideas?
2 Answers
  • Spoon Sports
    Spoon Sports 12/5/2011
    make sure the vacuum hose on the fuel pressure regulator is on, on the bottom of the fuel pressure regulator on the fuel rail, its a small black vacuum line that hooks to the nipple of the regulator. OR it might be the refrigerant (A/C) pressurizing or something. My MCS does not do this, but my other vehicles do this after driving w/ the A/C on. The hotter the day, the longer it "hisses" for.

    Try running w/o the A/C on (even better w/ the whole auto a/c system shut down), and see if your car hisses at you after a drive.


    I might be the supercharger, i blieve the S has one equiped. Whether it's somehow depressurizing or coasting to a stop, you can hear it because the engine is off.

    By the way, welcome to the club, you are not alone
    Spoon Sports
    physed 12/6/2011
    Thanks for the help. I understand there may have been an issue with some of the fuel pumps on Minis, so I'll start with the vacuum hose on the FPR. I'll let you know what the outcome is.
  • Spoon Sports
    Spoon Sports 12/13/2011
    Sure thign chief.


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