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2.5 tdi quattro AFB engine flat spot

Discussion in 'Diesel forum' started by audi2.5tdi, Nov 7, 2013.

  1. audi2.5tdi
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    audi2.5tdi Member

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    [Nov 7, 2013]
    recently bought a B5.5 2.5 TDI Quattro

    Firstly I removed the turbo elbow and did the old "mr muscle" cleaner in and moved the vane actuator, car seemed to be a little more responsive, ive got a flat spot now, seems to be around 2500/2800 - 3100/3200 rpm, pulls fairly cleanly then flat, then pulls stong again

    plugged the car into a scanner today and we got 2 codes, 546 and 575

    the first one seems to be something to do with the connection between scanner and car, the second comes up as the MAP sensor

    so i took the MAP sensor out of the NS intercooler (what a PITA!) snapped one of the screws! devil of a job getting that out!!

    cleaned off the MAP sensor with some brake cleaner and put it back, not sure it its done anything really, still seems to have a flat spot

    any body else had this or suggest anything else it could be?
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  3. adamss24
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    adamss24 Well-Known Member

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    [Nov 7, 2013]
    I would change the MAF sensor first especially if the turbo actuator moves freely from min to max when you pull the rubber vacuum pipe- sign that the N75 is working fine. If you have VCDS then you can cycle the valve on and off so it shows if it works properly. Depending on mileage worn nozzles and worn pump heads will also account for loss of power, replacing the nozzles usually restores lost ponies !
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  4. audi2.5tdi
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    [Nov 7, 2013]
    would the maf not have come up on the scanner as a fault? i dont have VCDS to check the frequency valve
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  5. adamss24
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    adamss24 Well-Known Member

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    [Nov 8, 2013]
    Maf will only come on diagnostic if open circuit or shorting to +/-
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  6. audi2.5tdi
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    [Nov 12, 2013]
    right, got hold of vcds today to try and track down the running problem with the car, ran the auto scan

    only fault code recorded was 00575 08-00 control limit surpassed

    the car seems to go "ok" but when your under full throttle it goes flat sometimes then picks up again

    I checked the tdi timing aswell and the timing seems to be retarded

    [​IMG]

    would this explain anything?

    also i ran a log whilst driving, expected boost vs actual boost

    it seems to be over boosting, then cutting it ive seen upto 2.3bar! doesnt sound right!?

    if anyone can read and interperate this data (excel file) pm me your email and ill email it over

    also using vcds i checked the n75 valve, and looking at the vnt actuator, every 10 seconds or so the actuator would fully move up, then 10 or so seconds later move down, and it did this as long as i left the measuring block running

    it moved up and down freely and seemed to move full travel


    is there anything else i can try to diagnose the problem using vcds (and how to do it)
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  7. darysas
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    darysas New Member

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    [Nov 14, 2013]
    get.jpg
    meaby you adjusted that nut?
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  8. audi2.5tdi
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    [Nov 14, 2013]
    not touched it
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  9. adamss24
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    adamss24 Well-Known Member

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    [Nov 14, 2013]
    Do not touch that nut yet, whilst not very difficult to adjust with a bit of know how and computer, i would leave it as it is for the time being. How is the airflow ? The MAF or boost sensor can give same symptoms as well as worn nozzles...
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  10. audi2.5tdi
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    [Nov 14, 2013]
    how do i test the airflow (i do have vcds available now)

    im replacing the timing belts, water pump, thermostat all rollers, tensioners and damper tomorrow

    i will adjust the tdi timing with vcds

    I think i want it to be above the mid line but below the top line is that right?

    should i be aiming for the middle of the mid/top lines or nearer one or the other?
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  11. adamss24
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    adamss24 Well-Known Member

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    [Nov 14, 2013]
    Can you send me the csv file/boost log please but not in excell, need to see it as it is from vcds. Please log measuring blocks 11, 8 and 1.
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  12. audi2.5tdi
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    [Nov 14, 2013]
    will see what i can do tomorrow (when are the parts we've been talking about via pm available?)
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  13. adamss24
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    adamss24 Well-Known Member

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    [Nov 14, 2013]
    Injectors and turbo ? I have them off the car already...
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  14. audi2.5tdi
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    [Nov 14, 2013]
    and chip/remap
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  15. audi2.5tdi
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    [Nov 14, 2013]
    *just checked, "psi tuning chip"
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