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Maf sensor problem

Discussion in 'Engine, Drivetrain, Fuel and Exhaust' started by ggc1973, Jan 8, 2017.

  1. ggc1973

    ggc1973 New Member

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    Your Mercedes:
    C220 CDI sport 2009
    I have recently replaced the maf sensor, the car worked fine for about 10 miles then started running bad again, when i unplug the maf sensor it makes no difference to the idle of the engine, does this mean its the maf again or does mean there is a different problem, the engine struggles and seems to mis fire worse around 2000rpm also the car is only giving me 24mpg, any ideas
     
  2. LostKiwi

    LostKiwi Senior Member

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    Does the car run better when driving without the MAF?
    With no MAF the car will run off the map with no adaptations from other sensors (lambda for example).
    If the car runs badly with the MAF disconnected your problem is likely to be elsewhere.
    If it runs fine then it may be the MAF or any sensor which feeds into the adaptations (MAP, Lambda etc).
    A STAR session should show where the issue is.
     
  3. AMck

    AMck Senior Member

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    Was it a genuine MAF? Aftermarket ones can often cause problems as bad as an old genuine, poorly MAF.
     
  4. Steve@Avantgarde

    Steve@Avantgarde Forum Supporter Authorised Forum Supporter

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    Its not a HFM-MAF sensor so unplugging it will make no difference, whether its good or bad. Its a volume and temperature sensor so needs to have a live, earth and PWM signal at all times.

    Assuming the MAF is good, your fault has been misdiagnosed. I have only ever replaced 1 MAF sensor on the updated 646 engine, they rarely go wrong. Assuming you have fitted a cheap aftermarket MAF then replace it with a genuine or OE component.

    Assuming once again you have seen a MAF fault code, if you have indeed checked the codes, then be aware the engine ECU can go to limp mode by pulling the signal wire from the MAF, just to generate a limp mode, it will then flag a fault code, but its code will be specific, for example - short circuit to ground or signal implausible - which is a limp mode generating code, not an actual fault.

    My guess would be you have an air leak, hence your loss of performance and poor fuel economy.
     
  5. OP
    ggc1973

    ggc1973 New Member

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    Hi Steve, thanks for the reply, it was an aftersales MAF sensor, what is really bugging me is twice the engine light has gone off over night and both times the car runs fine and the economy creeps back up to the 30-40mph, yesterday the car was running rough when i accelerate it judders like its being starved of fuel, but it always seems to be worse around the 2000rmp mark til it either gears down or gears up past it, the car is an automatic. Im not sure if this makes sense to you but the guy in my local merc garage told me that if the gearbox mount is badly worn and with the car being a rear wheel drive it can affect the performance of the car because when i accelerate it un-aligns the engine and the shaft to the back wheels, then advised me to have that done to see if it fixes the issue, he said this without putting it on the ramp to even check the gearbox mount, i`m quite bedazzled by this, can you advise please
     
  6. om613

    om613 Senior Member

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    Name that Garage!
     
  7. Steve@Avantgarde

    Steve@Avantgarde Forum Supporter Authorised Forum Supporter

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    The garage is not wrong, a worn engine/gearbox mount can most certainly pull the selector of the gearbox into neutral, but I dont think that is your fault from your description.

    My advice would be to refit your genuine MAF and seek an independent who has access to STAR diagnosis. The star machine can check all live data and actual values and should pin point your fault within 45 mins. Unless its a bit of a headscratcher.

    It sounds like a boost issue or possibly a blocked exhaust, but the fault codes will reveal more.
     
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  8. steveclv

    steveclv New Member

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    I'm not experienced on Mercedes but on the Fords that I have worked with we have never replaced a MAF - but we have cleaned them on many occasions. They use a hot wire to detect the airflow and air density and the wire can become coated with crud over time. Using a spray carb cleaner will bring it back to sparkling clean again (never, ever touch the wire with anything!).
    So give the original a clean and replace it and then as others have said, start looking for the cause of the problem elsewhere :) Good luck
     
  9. OP
    ggc1973

    ggc1973 New Member

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    Thanks for that, i think i will do that, clean the old one and put it back on as its an original part and the replacement is an aftermarket product, i`ll keep you posted if it works
     
  10. Paul1948

    Paul1948 Senior Member

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    A while ago I had many similar faults on my W220 320 cdi and was advised to disconnect the sensor and if the car ran more or less as it should the Maf sensor was faulty, cleaning recommended... no effect.. so purchased a used one for £15 off ebay instead of riking paying full price for a new genuine one, cured the problem and still running 10K miles later so sensors DO FAIL....maybe my sensor if different to yours... good luck withthe fault finding
     
  11. om613

    om613 Senior Member

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    Sorry if my response seemed flippant.
    Just that they seem to have advised the OP on a fix, without looking at the car.

    Worn mounts, couplings, bushes etc. can be spotted by Indys and the degradation pointed out.
    Or even anecdotally - 'we change loads of these on this model'. Did they say so?
     
  12. Steve@Avantgarde

    Steve@Avantgarde Forum Supporter Authorised Forum Supporter

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    Your MAF isn't all that different in your engine however the MAF's in the OM648 fail all the time, I have only ever replaced 2 on an OM646's. And from the information the OP is giving us, its not concurrent with a MAF failure.
     

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