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  1. #1
    WJ Fier
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    Disableing backfire on cold start

    For the third time in apx 20 months an extremely loud backfire occurs on start and the car is disabled and must be hauled to the BMW of Austin service dept. The explosion was so loud it brought my neighbor out of his house to investigate.
    The intake manifold must be replaced. The stated cause is " fault air mass meter caused engine to run lean causing a lean misfire in the intake....."
    Has anyone had similar problem?

  2. #2
    Robert Platt Bell
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    If a car engine runs too lean, it can cause detonation, which is a condition that occurs when instead of a nice uniform flame front, you get a sudden explosion of the fuel/air mixture.

    If the MAF was bad, it may cause that sort of problem. A large air leak can also do that. I was servicing my car and tried to crank it, not realizing I didn't have the MAF hooked up all the way and got the same backfire (BAM!) which wrecked the MAF ($250 on Pelican). I think it also took out the Idle Air Control valve. I replaced both, along with the cyclone separator and associated hoses. See link.

    I could see where that would cause problems with your intake.

    Be sure to change the cyclone oil separator and lines with the updated and upgraded parts. It is probably due for new ones (you have a 3.0 or a V-8? I have the 3.0).

    It may have been some kind of intake leak (intake elbow, cyclone separator) causing the problem, which finally caused a backfire large enough to crack the plastic intake.

    Let's hope there wasn't any internal engine damage.

    As you can see, the intake manifold is is a pretty complicated piece of plastic....

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