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98 2.5 tdi a4 - no boost from the turbo help

Discussion in 'A4/S4 forum(B5 Chassis)' started by turbozx, Feb 2, 2012.

  1. turbozx

    turbozx New Member

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    as above really the car is really slow and struggles to rev above 3000 rpm, no turbo kick.

    Starts fine/ no smoke/ doesnt use oil turbo shaft has very little play and spins free.

    Put a boost gauge on it today (plumbed into the feed to the boost soleniod) and it only shows a vacumn when driving.

    Can anyone point me in the right direction - i suspect the wastegate flap is stuck open?? I'm more use to petrol turbo cars than diesel.
     
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  3. towcestervag

    towcestervag Member
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    get diag test done and post results
     
  4. diffas

    diffas Member

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    Sounds like wasted MAF.
     
  5. PAULF

    PAULF Active Member
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    Try to move the actuator by hand, the turbos' variable vanes often soot up and stick.. If it doesn't move up and down, search this forum for the Mr Muscle clean thread to fix it.
    If you have access to VCDS, check for over-boost codes, and try the actuator vacuum test.
     
  6. turbozx

    turbozx New Member

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    The wastegate arms moves up and down ok - this can been seen when I start and stop the engine, I have run the car with the Maf dissconnected and it does seem too be a bit better slightly more power and reving to 4000 rpm easier.

    I take it having the MAF disconnected puts the ECU in a reduced performance mode
     
  7. murran

    murran Well-Known Member

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    yes and no.
    with the airmass meter plugged in the ecu will read it and fuel accordingly. even if the airmass is faulty and reading half the amount of air that is actually going in.
    basically at idle theres say 200grammes per second of air. full boost theres 1200 grammes per second.
    you unplug the airmass, the ecu sees its open circuit and subtitutes the actual value produced by the airmass (which isnt there anymore) with a set figure of 550 grammes per second. a medium value.
    you getting the idea?
    to improve by unplugging it it must be reading less than 550 when it should be reading 1200.

    you really need to get it on the diagnostics to do a running actuator test of the boost control system. as you can run this test independant of airmass fault limitations.
    basically you set the test in motion on the diagnostics and the ecu increases the idle speed to 1300 rpm. it then switches the boost control soleniod from 0% to 100% and back every 5 seconds. this works the variable vane in its full plane of motion. on the diagnostic it displays the signal from the boost pressure sensor. if all this looks ok. you can rule out any boost control faults in about 2 minutes without even opening the bonnet!
    you can do exactly the same sort of test with the egr, rotary pump advance retard. etc.
    the only thing left is the airmass.......
     
    #6 murran, Feb 3, 2012
    Last edited: Feb 3, 2012
  8. turbozx

    turbozx New Member

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    I only have basic vagcom fault codes were as followed

    00550
    00523
    00553 bear in mind i had disconnected the maf before hand


    I cleared the fault codes went for a drive and scanned again with no codes


    I measured block 003 MAF specified vs actual and the actual never went over 600 when specified was 900,
     
  9. murran

    murran Well-Known Member

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    hmmm, id be buying an airmass meter then.
     
  10. turbozx

    turbozx New Member

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    changed the MAF for a new Bosch one - made a slight improvement.

    How do you plumb in a boost gauge on these cars?
     

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