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on going boost problem, help please.

Discussion in 'A3/S3 Forum (8L Chassis)' started by jay1601, Jan 13, 2011.

  1. jay1601
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    jay1601 Well-Known Member

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    [Jan 13, 2011]
    First mod I did to the car was a boost gauge. Was pulling inbetween 4-5 psi. As shown on a cheap autogauge. Then did a fault check and got fault with the temp sensor. I have fitted a front mounted intercooler, just incase of a leak with the standard one. All fitted right. Got a TurboSmart gauge now, did some logs, 1st gear to 4th gear only pulls 3PS- 5th gear pulls 4-5 psi any help would be good thanks
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  3. s3dave
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    s3dave TFSI Hybrid

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    [Jan 13, 2011]
    If you havent got leaks i think it may point to the n75 valve, have you got any mates to swap to see if it performs better?
    also 5 psi could be running in limp mode have you scanned it?
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  4. jay1601
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    jay1601 Well-Known Member

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    [Jan 13, 2011]
    yeah i have. found no fault codes.

    have disconnected the battery to reset the ECU.
    u haven't got anyone that has a VAG. so can't borrow a N75 valve. any ways of checking this without swapping it ?

    thanks Jay
    #3
  5. Speedy Steve
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    Speedy Steve Active Member

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    [Jan 13, 2011]
    yes does sound like its in limp mode get the system pressure checked for leaks (best way) also check hoses to and from N75 and actuator if none then id be looking at the N75 but you should have a fault coming up
    #4
  6. jay1601
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    jay1601 Well-Known Member

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    [Jan 13, 2011]
    is they a way to bypass the N75 valve. just for a test, not as a perm fix ?
    #5
  7. jay1601
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    jay1601 Well-Known Member

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    [Jan 13, 2011]
    been having a look around online, few places have been maybe check the wastegate aswell. anyways of checking this, as its not the easiest to see on the A3 ?
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  8. jay1601
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    jay1601 Well-Known Member

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    [Jan 13, 2011]
    Just driven my car. Not sure if the boost gauge is way out on its reading. But I can head a sucking noise and its dumping air when its reading -4 upwards.

    What would this be, the boost gauge or something else I need to take a look at?

    Thanks Jay
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  9. s3dave
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    s3dave TFSI Hybrid

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    [Jan 13, 2011]
    you can disconnect the actuator pipe from the n75 and see if drives differently, nice and steady and it should open on actuator pressure about 8 psi
    but if you can hear air, you really need to have a good luck for leaks, a good sign of a split pipe is oily residues near the, or on the pipes
    #8
  10. jay1601
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    jay1601 Well-Known Member

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    [Jan 14, 2011]
    I disconnected the actuator pipe. Took the car for about a 8 mile drive. It boosted lovely didn't push it above 10 PSI. I have reconnected the hose just incase it can cause turbo damage would this mean that the N75 valve needs replacing?

    Thanks jay
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  11. Welly
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    Welly VX220 SC Driver :)

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    [Jan 14, 2011]
    Not necessarily - what engine is it?

    EDIT: Sounds like the turbosmart gauge is a bit duff to me if it's reading less. AutoGauge boost gauges are normally pretty good.
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  12. jay1601
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    jay1601 Well-Known Member

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    [Jan 14, 2011]
    Its the AGU block. I don't think its just the gauge. While it was disconnected pulled a lot better and could hear the tool spool

    Any other common problems with this sort of this?
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  13. Welly
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    Welly VX220 SC Driver :)

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    [Jan 14, 2011]
    I don't, not even for a second, think that it's a gauge issue. I was just saying it's something to be aware of.

    Bear in mind that when the actuator pipe is disconnected, the boost is uncontrolled, meaning that the turbo is working ok, it's something electronic stopping the boost from appearing.

    N75 is a possibility, but to be fair, I'd say unlikely. They are pretty simple thing, basically a glorified on/off switch and rarely fail. When they do fail, they normally throw a fault code to suit. Firstly, is the N75 the right way round? A photo will help confirm this.

    Secondly, AGU engines are very very highly reliant on the MAF. They have no MAP sensor to tell the engine management what the actual boost level is in the manifold, and therefore it has to be worked out via an airflow vs throttle body angle calculation. Thus the MAF does play a big element in boost control on the AGU engine (I speak from experience).

    Here is what I would do.

    If you have VAG COM and can log, you should be able to log block 118. It won't show actual turbo pressure, but it should still show N75 duty cycle, and this will tell you whether the thing is working or not, and if so, how much.

    Secondly, I would try and find another MAF just to use for testing. Second hand, borrow, beg, whatever. Anything to use a MAF which is known to be working to save you potentially buying one when you don't need one.

    Start by logging N75 duty cycle (if you can on the AGU). If you need to start replacing parts (on the proviso that the N75 is OK), start with the MAF - it's the most likely culprit.
    Last edited: Jan 14, 2011
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  14. jay1601
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    jay1601 Well-Known Member

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    [Jan 14, 2011]
    I don't have vag come mate. Got a fault code reader. Doesn't find any faults.
    What sort of thing should I see if the MAF is going? Car runs fine just slower compared to normal and only shows 3-5 PSI peaking

    I don't have another MAF to borrow. Don't want to start buying new parts if I can help it

    I will try to get some pics up when I get back from work. If its not to dark

    Thanks Jay
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  15. Welly
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    Welly VX220 SC Driver :)

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    [Jan 14, 2011]
    This sort of problem is a trial and error job mate I'm afraid.

    If there are no fault codes to help you, then it's time to start changing stuff. I know that's frustrating, but that's how it is really.

    Photo of the N75 will confirm it is the right way round, at least that's a start as that's surprisingly common.
    #14
  16. jay1601
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    jay1601 Well-Known Member

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    [Jan 14, 2011]
    The car was 100% standard when I bought it, so I would assume its fitted right. Most work has been carried out by audi. I will try to get a photo up asap. should be around 4.45 ish
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  17. Welly
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    Welly VX220 SC Driver :)

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    [Jan 14, 2011]
    OK, no probs. Worth checking none the less to be fair.

    You got any scrappers local to you? Might be worth trying to get an N75 to try. Failing that, I have an N75 valve I could send you to test with I suspect, I will have a hunt round in the garage later on.
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  18. jay1601
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    jay1601 Well-Known Member

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    [Jan 14, 2011]
    heres the photos. sorry not the best as its getting dark already

    is this fitted right ?
    [​IMG]
    [​IMG]
    #17
  19. Welly
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    Welly VX220 SC Driver :)

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    [Jan 14, 2011]
    Yeah, looks to be fitted fine from memory... I will double check when I get home, but sure that looks right.

    Looks like you move on to testing stuff then dude :(

    Start with the N75, it's the cheaper one to do first. I'll see if I can find my spare one.
    #18
  20. jay1601
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    jay1601 Well-Known Member

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    [Jan 14, 2011]
    :( can't afford to start doing that

    i will take your advice and start with the MAF sensor.

    just need to find someone with a VAG that will let me borrow a MAF.
    #19
  21. Stanley
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    Stanley Member

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    [Jan 14, 2011]
    Is running the car without N75 connected bad for it at all?

    Im suffering a similar problem on my AGU and would like to test the functioning of the wastegate/N75 and dare i say it, turbo.
    #20
  22. jay1601
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    jay1601 Well-Known Member

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    [Jan 14, 2011]
    Bit more info. I disconnected the MAF and took it for a drive. It would boost to about 2-3 PSI then just go flat. It put up a fault code for being to low volts or something.

    So I'm guessing the MAF is working ok?

    I still think it could be the N75 but don't want to just start buying new stuff for the sake of it

    Anymore help/info would be appreciated

    Thanks Jay
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  23. s3dave
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    s3dave TFSI Hybrid

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    [Jan 14, 2011]
    Last edited: Jan 14, 2011
    #22
  24. s3dave
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    s3dave TFSI Hybrid

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    [Jan 14, 2011]
    It should open under actuator pressure so as long as you are steady it will be ok, for a check only...needs to be operating correctly asap
    #23
  25. cerbera4_0
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    cerbera4_0 New Member

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    [Jan 14, 2011]
    Just as an side. do you know the stock boost pressure for an S3 2000 model (APY).
    #24
  26. jay1601
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    jay1601 Well-Known Member

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    [Jan 15, 2011]
    update.

    looked over all boost/vac pipes. cannot find any split/cracked pipes. all the clips and fine.
    took the TIP off cleaned it. again no splits or anything
    MAF is clean inside.
    DV is fine (not even a month old yet) Forge 007P
    anyone got any ideas ?
    #25
  27. jay1601
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    jay1601 Well-Known Member

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    [Jan 15, 2011]
    MAF has now been cleaned. using Audi contact cleaner.

    the MAF on the car has been on it since new 25/1/99 found a sticker with a date on it.

    good chance it could be failing ?
    #26
  28. jay1601
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    jay1601 Well-Known Member

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    [Jan 15, 2011]
    just driven the car with the cleaned MAF, i also cleared the code for MAF.

    as i first drove away the car pulled well, went to about 5PSI then just went flat and dropped back down to 3PSI.

    the car will still pull ok throught out the rev range but only to a max of 3-4PSI

    what are the normal symptoms of a broken/dying MAF ?
    #27
  29. s3dave
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    s3dave TFSI Hybrid

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    [Jan 15, 2011]
    If you took the actuator of the n75 and it boosted up ok then i think the maf is proberbly fine i will see if i have a n75 valve kicking about for you to try
    #28
  30. jay1601
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    jay1601 Well-Known Member

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    [Jan 15, 2011]
    if i take the actuator pipe off, it will boost no problems. just got to be careful of over boost then.

    that would be really good cheers mate
    #29
  31. jay1601
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    jay1601 Well-Known Member

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    [Jan 16, 2011]
    took the battery out today as i needed to change sidelight bulb for the MOT nwxt week. left it out for about a hour to reset the ECU. as soon as i put the battery back in and drove the car. i got another max boost code. (sorry for bad photo taken wtih my BB)
    still wouldn't boost over 3 PSI after the reset ECU
    [​IMG]
    #30
  32. jay1601
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    jay1601 Well-Known Member

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    [Jan 26, 2011]
    had my bosses son look at my car today (Audi technician) he used VCDS found 0 faults. looked at the readings, only thing he could find was the MAF readings was only a little bit down.

    checked all pipes, found 0 splits or cracks. replaced the N75 valve. he said the turbo might be on the way out, but if i take the wastegate pipe off it will boost 15+ PSI.

    he checked all the common faults and found nothing. so really confused now

    anyone got any idea's ?
    #31
  33. s3dave
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    s3dave TFSI Hybrid

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    [Jan 26, 2011]
    You really need to log the actual v requested boost to see what is happening,
    #32

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