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Thread: Detonation at load

  1. #1
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    Detonation at load

    Good afternoon
    Recently, my car has been sluggish. When I get on the gas, i often get the metallic pinging sound associated with knocking or detonation in the combustion chamber. It doesnt seem to be a common problem for these cars.
    I have no CEL, and do not yet have a code reader.
    I read on the M5 forum that a guy had a failed head gasket which led to these symptoms. I'm hoping it doesnt come to that.
    Car also is hesitant, and will have a random dip in rpm at steady throttle application.

  2. #2
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    If it was really knocking, you would get a check engine light. If it keeps knocking then the CEL will go from solid to flashing.

    Have you cleaned the MAF sensor? What intake and air filter do you have?

  3. #3
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    What octane gas do you use?
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  4. #4
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    Bad coil
    ME:"I want to make my car faster and lighter"
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  5. #5
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  6. #6
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    Seems it might be bad gas combined with oil getting into combustion chamber. Wife put reg gas in the tank and I believed I had already burned it all off, but it took a few more gas half fillups and the sluggishness is mostly gone.
    I also recently changed the spark plugs and they had SEVERE buildup on a few. Saw oil pooled in spark plug area as well. Looks like my valve cover gasket needs to be changed..

  7. #7
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    What kind of "SEVERE buildup?" If hard, the car is not being driven hard enough; if soft and sooty, burning oil.

    The DME can retard spark timing to dial out detonation. This will degrade performance.

    What is the minimum octane rating posted on the gas filler cap? Mine says 89.
    Last edited by edjack; 10-18-2017 at 11:24 AM.


    Ed in San Jose '97 540i 6 speed aspensilber over aubergine leather. Build date 3/97. Golden Gate Chapter BMW CCA Nr 62319.

  8. #8
    geargrinder's Avatar
    geargrinder is offline Having No Trouble Here BMW CCA Member
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    I bet they were zillion mile crapped up plugs. Crap plugs + bad gas... those deposits get red hot then - bingo - knock. Misfire would be different and would set a code. This sounds clearly like detonation, and a fouled up plug can do that.
    2003 M3CicM6 TiAg
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  9. #9
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    This doesn't sound like a bad coil.

    Stumbling under heavy load is more likely to be a bad spark boot. An oil-soaked boot degrades faster than a dry boot.

    Does your engine burn more than one quart of oil per thousand miles?

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