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MAF SENSOR ON TDI

Discussion in 'A4/A4 cabriolet/S4 forum(B6 chassis)' started by clough103, Dec 31, 2010.

  1. clough103
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    clough103 Member

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    [Dec 31, 2010]
    Im still on my determined mission to find out why my car is so **** on fuel.

    Trying a bit of trial and error, am starting with the MAF sensor.

    If i disconnect it what will happen? will the car run default values etc and will it put the car in limp mode or generate the EM light?

    cheers
    #1
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  3. 19scotty81
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    19scotty81 Push down and across !!!!!!!!!

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    [Dec 31, 2010]
    Hi, sorry i'm new so you've probably already told people but whats your figures ???????
    #2
  4. clough103
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    clough103 Member

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    [Dec 31, 2010]
    struggle to get 30 in town and if i make 45 on a run ive done well and thats driving it sensibly.

    ive got a big thread going called 130 TDI economy and have posted some bits today on the new 'mpg' thread
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  5. Turkster
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    Turkster Bro.Paul 2.5TDI Quattro Sport

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    [Jan 1, 2011]
    a new maf unit never hurts the MPG for sure mate, they also have a life span of about 12-18 months depending on your driving style, new air filter is a must at the time of change,
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  6. clough103
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    clough103 Member

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    [Jan 1, 2011]
    well i have cleaned it with contact cleaner but it didnt make any difference. I didnt fancy shelling out for a new one if it isnt going to make any difference. I know on other cars if you disconnect the sensor the ECU runs a sort of default program (in which case if the MAF was faulty the MPG should improve then i will know to go and buy a new one)

    This is why i need to know what happens if it is disconnected as i know the Audis are a bit complicated and i didnt fancy buggering something up
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  7. paul20v
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    paul20v Audi fanatic

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    [Jan 1, 2011]
    If you unplug it yes it will go into limp mode
    i dont understand what you are going to achieve by doing this to be honest .
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  8. clough103
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    clough103 Member

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    [Jan 1, 2011]
    i will explain by giving an example, simple really.

    My other halfs Punto JTD had a MAF sensor problem. MPG was really poor and it wasnt running its best. On disconnecting the sensor the car runs a default reading stored on the ECU and thus the car suddenly became a whole load quicker and the MPG went back where it should. Thus indicating an obvious MAF problem, changed MAF sensor plugged back in and voila Punto running as it should once again.

    This is exactly what i was hoping to achieve once again by simple free DIY stuff to find out if the MAF is causing the poor MPG on my A4
    #7
  9. quattro tony
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    quattro tony Member

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    [Jan 1, 2011]
    I can see where you are coming from as ive disconnected the maf on some cars that were dead and noticed a difference that led me to believe the maf was at fault, but i have to agree with paul20v if you disconnected yours i don't think you will find it makes an improvement unless your mass meter was shot.The only way to check them properly is with diagnostic like vag com where you can compare the values of the mass meter.
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  10. paul20v
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    paul20v Audi fanatic

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    [Jan 1, 2011]
    Limp Mode
    this is what happens if you disconnect the audi maf
    it will not rev above 2k
    so you will notice a difference but its not going to help you .
    #9
  11. clough103
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    clough103 Member

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    [Jan 2, 2011]
    well thats why i was asking. seems i cant try that then lol
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  12. Turkster
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    Turkster Bro.Paul 2.5TDI Quattro Sport

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    [Jan 2, 2011]
    the only way to know mate is to plug it in to VAG com or try another unit on the car,
    #11
  13. paul20v
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    paul20v Audi fanatic

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    [Jan 2, 2011]
    Not having a dig but i would never swap out electrical components
    you never know it may be the car or wiring at fault and then you destroy the swapped part too
    not that im saying thats whats wrong here its just air on the side of caution when swapping bits from another car .
    #12
  14. clough103
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    clough103 Member

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    [Jan 2, 2011]
    i wouldnt know where to get another one from without actually buying one. will have to get it plugged in at somepoint and see what comes up i guess
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  15. Cheshire-Autotech
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    Cheshire-Autotech Mobile Remapping & Diagnostics VCDS Map User

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    [Jan 2, 2011]
    Clough103,

    A couple of things to try, breezing thru the thread briefly, others have suggested I see... (sorry to repeat)

    1. Disconnect MAF sensor first. If the car runs exactly as it does with the sensor plugged in, then your MAF sensor is fine. If it runs better when its disconnected, then its Knackered, replace immediatley with genuine replacement part (do not use NON OE Sensors) these are more trouble than they are worth.
    2. Check the EGR (Exhaust Gas recirculation) Valve. They can get clogged up with Crud and the flap can stick, causing wierd performance qualities. Poor acceleration,poor MPG etc.
    3. Diesels take ages to warm up....... No point in taking any MPG readings until 10 minutes + on the road. 45 MPG on an avant aint that bad mate. Max you will see will be high 40's... IMHO

    Out of interest, :-
    A - How long have you had the car?
    B - Has it always made those MPG figs?
    C - When was the car last serviced?
    D - Mileage?

    Again as others have suggested, get yourself down to someone with VCDS (formely known as VAGCOM). You will possible save yourself a load of time and avoid changing or messing with something on your pride and joy that is actually working 100%.

    If you are in Cheshire or nearby, PM me and I will plug in and have a look.

    Good Luck

    Blair
    #14
  16. paul20v
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    paul20v Audi fanatic

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    [Jan 2, 2011]
    Not being funny here but if you had read the thread you would see that i have already said that if you disconnect the air mass meter that the car goes into limp mode this wont help
    yes some cars will run tidy on base setting with the air mass disconnected but the 1.9TDi PD wont .
    #15

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