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Thread: Running better with MAF unplugged

  1. #1
    Join Date
    Aug 2016
    Location
    Vancouver, BC
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    My Cars
    2003 BMW Z4

    Running better with MAF unplugged

    Some background info
    2003 Z4 3.0 M54 engine
    140,000km

    Z4 has been having issues with poor fuel economy (15l/100km), and poor pickup in the lower revs (<3000rpm)
    At times getting P0301 code as well. Swapped ignition coils but problem stayed on cylinder 1.

    Intake boot had tear so that was replaced earlier. I have also changed spark plugs and cleaned the MAF with MAF cleaner.

    Earlier this week, I wanted to try unplugging the MAF and seeing how it ran.
    Surprisingly, it ran much better. Much better pickup and maybe better fuel economy but I haven't driven enough to prove it yet.

    Does this definitively point to a bad MAF or could there be other things at play?

  2. #2
    Join Date
    Oct 2015
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    Alabama
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    My Cars
    97 BMW M3 Sedan
    I would try to clean it with some MAF cleaner. Make sure it fully dries before plugging it back in.

    If that doesn't work you might be able to get a MAF from a yard since there should be plenty of M54 engines around.
    Current
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    Past
    -2001 BMW 325i
    -1999 BMW M3 Vert White
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  3. #3
    Join Date
    Dec 2013
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    EXOTICS
    Poor fuel economy coupled with misfires indicate an intake leak causing lean fuel mixtures.
    Disconnecting the MAF causes the engine to run in open loop, the result being overly rich fuel mixtures.
    I feel your intake leaks didn't end with the intake boot replacement, you'll have to search further.
    A smoke test of the intake system, performed with a professional smoke machine,
    is the best most reliable way to locate and confirm all intake leaks.

  4. #4
    Join Date
    Jan 2008
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    Arida Zona
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    30,108
    My Cars
    z3
    BMW MAFs can NOT be cleaned - only certain MAFs used on Fords and a few other manufacturers in the 90's were the technology that could be cleaned
    "Cleaning" a BMW MAF will at best do nothing, at worst ruin it

    Check for vacuum leaks first, if the car is running rough due to vacuum leaks unplugging the MAF will force the system to run in a default setting. If the MAF is plugged in and telling the engine X amount of air is coming in, but its also receiving Y amount of air from a vacuum leak, it can run rough but unplugging the MAF will fix that. The CCV can be another potential source of vacuum leaks if it has failed. Have it smoke tested if you can or if you can't and see no signs of visible leaks, try to swap a good working used MAF (any friends with the same engine as you?). Don't buy a cheap china/ebay MAF whatever you do. A working used OEM MAF is better than a China crap part.

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  5. #5
    Join Date
    Aug 2016
    Location
    Vancouver, BC
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    2003 BMW Z4
    Thanks for the input guys! I'll take it to a shop to professionally smoke test and start the hunt for a used MAF
    Will update in a week or two

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