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Thread: Culprits of lean or rich conditions in an M119 engine?

  1. #1

    Culprits of lean or rich conditions in an M119 engine?

    What are the typical reasons for a lean condition in an M119 engine?
    Rich condition?

  2. #2
    E500E Guru
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    Re: Culprits of lean or rich conditions in an M119 engine?

    vacuum leaks and bad sensors (maf o2 etc)

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    Re: Culprits of lean or rich conditions in an M119 engine?

    Correct -- the condition would be caused by bad inputs into the system. Potentially these could be a vacuum leak within the intake system, or a faulty MAF or oxygen sensor signal back to the computer that causes it to make incorrect adjustments. The intake air temperature sensor in the driver's side air intake stream is also a system input.

    An EGR problem could also be a contributor (but I've seen the EGR to be pretty reliable).

    A vacuum leak will usually cause the engine to run roughly and/or at a higher idle.

    My guess, as Al says, would be a bad MAF or oxygen sensor returning a faulty signal. It's a good idea to replace the intake air temp sensor - they are under $20 new as OEM pieces.

    Cheers,
    Gerry

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  6. #4
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    Re: Culprits of lean or rich conditions in an M119 engine?

    IAT won't affect the AFR... it's only there to retard timing if it reads excessively high temps. The LH system bases most of the mixture info on the MAF and O2 readings, along with engine temp readings from the 4-pin sensor only.

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