Air Mass Sensors (MAF) explained
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    Air Mass Sensors (MAF) explained

    Some MAF datasheets from Bosch which are used in most BMW models.
    Attached Files Attached Files

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    simonsays (26-04-2012)

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    Which MAF? & Replacing it on the BMW Diesel Engine M47/M47N/M57/M57N

    A failing MAF in a BMW Diesel engine can present the driver with erratic idling, poor acceleration, flatspots and reduced MPG.

    It is recommended to fit genuine Bosch MAF's as even brand new pattern parts can have performance issues!

    All the following part numbers directly relate to BMW and Bosch part numbers, as you can see replacing the Bosch 0928400314 fitted to the early 320d's
    and some very early 330d's require the ECU recoding, this can be done at a reputable BMW specialist or dealers.

    Location and Cleaning
    The MAF is located on the offside of the engine in between the Air Filter and the Air Pipe which connects to the
    Turbo Inlet. The Bosch part number is found on the side of the housing.

    To remove the MAF unscrew the 2x 5 point Torx screws, you may find snapping the screws tamperproof pin and
    using a small bladed flat screwdriver the easiest option, then pull the sensor from the housing.Take care when handling the sensor!

    If you have the bonded MAF, Bosch 0928500529, the whole housing and sensor must be removed!
    Remove the electrical plug, unscrew the two allen screws, pull the air pipe from the MAF, remove the
    2 Torx screws and the MAF housing should simply pull away from the air filter housing. See pic below.

    Diagnostic scan seldom reveal MAF errors as although you can feel its failing affects they seldom fall below the monitored
    acceptable levels. A quick DIY test is to remove the MAF's electrical plug, tie it up securely and test drive the car.
    Power levels will be down but any idling issues, flatspots, acceleration hesitancy will not be present and the engine should
    rev smoothly thoughout the full rev range.
    Unfortunately disconnecting a EU4 engine MAF and testing as above will result in EML(Engine Management Light) illumination,
    this can be cleared once reconnected via diagnostics or when 'X' number of clear check cycles have been achieved.
    By check cycle I mean when the ingnition is switched on the car auto checks its systems, unfortunately I do not know exactly
    what number of clear check cycles are required to clear the EML?

    If you're convinced the MAF is at fault then you could opt for cleaning using an isopropyl alcohol cleaner or any electrical contact cleaner
    that won't leave a residue, CRC MAF cleaner is well documented on the net but check its ingredients for cheaper alternatives.
    If you have the bonded MAF you'll have to spray the cleaning fluid
    through the protection gauze to the sensor.

    If cleaning dosn't work then a new MAF is the only solution, as said stick with Genuine Bosch MAFs from reputable
    suppliers and shop around for prices as they do vary somewhat.

    Air Mass Meters
    Air mass meters home
    MAF Service GmbH - Luftmassenmesser-Shop
    Euro Car Parts | The UK's Number 1 Provider of Car Parts Online and In Store

    Last edited by simonsays; 30-04-2012 at 16:37. Reason: Links added

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    Emil (27-05-2012),NealP (29-04-2012),Scrumpy_j (05-02-2013)

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