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Thread: 2004 2.5TDI BAU intermittent flat spot - can you help, please?

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  1. 2004 2.5TDI BAU intermittent flat spot - can you help, please? 
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    A couple of months or so ago the allroad presented me with an apparently symptomless EML while we were on the way somewhere not relevant.

    Because that somewhere was quite a long way away, I called Green Flag. The code was 00575 Inlet manifold pressure exceeded - intermittent.

    Since there were no symptoms, we opted to clear the code and carry on. There was no further reoccurrence. Of anything.

    Until a month ago.

    This time there were symptoms. The first was a hefty flat spot when going transonic in 5th while merging with the M5 traffic, followed twenty five minutes later by a complete loss of power. Nothing else - no smoke, no misfire, no untoward noises.

    Just no poke. At all.

    I pulled off at the next junction, parked up and sat thinking about things for a while. Opening the bonnet confirmed that the engine was still there, which was encouraging. I wasn't in a position to do much other than check that as many of the many vacuum hoses I could see were still firmly attached, which they were.

    Gingerly I set off for home. Everything seemed fine, then ten minutes into the return journey the old girl threw the steady EML again.

    A day or so later the car was with the independent chap who does the big and complicated stuff. The code was the same 00575 as before.

    He checked everything relevantly checkable, including the actuator mechanism. Everything seemed fine and within parameters.

    I'd read the appropriate Ross-Tech 00575, which suggested either the turbocharger or the N75. The turbo appeared absolutely fine, so I made a decision to replace the N75.

    I like to think that I didn't fall into the trap of chucking new parts at it, but for a variety of reasons it made sense to put a new one in:

    a) I wasn't charged for the scan and the check over and was, notionally at least, 'in credit'.

    b) We'd discussed the probability of the N75 being at fault, and he thought that it was at least as likely to be that as anything else.

    c) A new one was relatively inexpensive and a doddle to swap out.

    d) Since I intend to keep this car for as long as I can, there's a case to be made for replacing a component like the N75 on the simplistic basis that they do fail.

    e) If it had a new N75 and the problem reoccurred, then at least it couldn't be that any more...

    Today, the flat spot came back.

    Only when accelerating hard in 5th, and only twice in more than a dozen attempts to provoke it into misbehaving. On one of the occasions the flat spot was no more than fleeting; on the other it simply would not pull even with my foot ankle-deep in the carpet.

    Every other time she pulled like gangbusters, just the way she should do. The motor was fully up to temperature, as it had been on the previous occasions when something went wrong.

    I didn't have to stop and kill the engine at any point; if I rolled off the throttle and tried again on the next straight bit of road it accelerated as normal.

    There is no EML this time, and no other symptoms whatsoever.

    So where to go from here, d'you think?

    The car has done a measly 71,000 miles, has lived exclusively on a diet of BP Ultimate (or its equivalent) for the past year, has only ever had supermarket diesel in it two or three times at most since I bought it brand spankers nine and a half years ago, and sleeps under a hand-knitted angora blanket at night.

    Where should we look next?

    Any suggestions gratefully received.
    Last edited by Phutters; 12-11-2013 at 09:54 AM.
     
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  2. Re: 2004 2.5TDI BAU intermittent flat spot - can you help, please? 
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    Option1, pull the hand knitted angora blanket gently aside, open the bonnet then take the turbo out and crack the hot side open. 75 percent chance you are now looking at the problem.
    Option 2, VCDS is your friend, measuring blocks- check boost in graphs. Put the missus in the drivers seat and drive around untill the problem occurs, while you're paying exclusivly attention to the graphs
     
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  3. Re: 2004 2.5TDI BAU intermittent flat spot - can you help, please? 
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    Quote Originally Posted by ametlib View Post
    ...take the turbo out and crack the hot side open. 75 percent chance you are now looking at the problem.
    Thanks for the reply.

    I appreciate that what I'm about to ask is probably difficult to answer without having the offending item in front of you, but I'll try it anyway.

    The problem as in sticking vanes, or the problem as in the turbocharger being (and I'll use a Norwegian word here) fårked?
     
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  4. Re: 2004 2.5TDI BAU intermittent flat spot - can you help, please? 
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    fårked !!! No I dont think your turbo is -- " sheep-ed" Was more thinking of sticking vanes. Manifold pressure exceeded makes me think of sticking vanes first, then N75
     
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  5. Re: 2004 2.5TDI BAU intermittent flat spot - can you help, please? 
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    Quote Originally Posted by ametlib View Post
    fårked !!! No I dont think your turbo is -- " sheep-ed" Was more thinking of sticking vanes. Manifold pressure exceeded makes me think of sticking vanes first, then N75
    Well, we know it isn't the N75, because this one is a new one.

    Unless the new one is bust as well, of course.

    We'll get those vanes checked next. I'm a bit puzzled why today's nonsense didn't give me an EML though. It has done before.

    If the vanes were sticking and causing the erratic boost (and erratic boost is what I've got), wouldn't you have expected the engine management light to have come on?
     
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  6. Re: 2004 2.5TDI BAU intermittent flat spot - can you help, please? 
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    A footnote:

    The turbocharger she is brokened. Hey ho. £360 for a rebuilt exchange unit with a two-year warranty from Midland Turbo.

    Bit of a no-brainer really. A brand new one over the polished granite parts counter at you-know-where is almost three times the price with the same warranty.
     
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  7. Re: 2004 2.5TDI BAU intermittent flat spot - can you help, please? 
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    Sorry to hear, but thats my experience too. A new N 75 goes in first but are very seldom the cure for boost issues , the turbo is
     
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  8. Re: 2004 2.5TDI BAU intermittent flat spot - can you help, please? 
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    Quote Originally Posted by ametlib View Post
    Sorry to hear, but thats my experience too. A new N 75 goes in first but are very seldom the cure for boost issues , the turbo is
    My glass is half full, Mr Ametlib.

    When this car falls to pieces around me and I'm sitting in the middle of the road in a pile of rust, at least I'll have an N75 and a turbocharger to put on eBay.

    They should pay for my bus fare home.
     
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  9. Re: 2004 2.5TDI BAU intermittent flat spot - can you help, please? 
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    i actually think you have had 2 problems. since replacing the n75, the eml hasn't come back on, which is indicative that the n75 was indeed faulty. the turbo was also faulty at the same time. if you had only replaced the turbo i think you would still be having problems.
    Last edited by zollaf; 15-11-2013 at 07:47 PM. Reason: changed my mind and decided not to do any editing.
    Audi 80 tdi avant with 360,000 miles...
     
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  10. Re: 2004 2.5TDI BAU intermittent flat spot - can you help, please? 
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    Quote Originally Posted by zollaf View Post
    i actually think you have had 2 problems. since replacing the n75, the eml hasn't come back on, which is indicative that the n75 was indeed faulty. the turbo was also faulty at the same time. if you had only replaced the turbo i think you would still be having problems.
    I think you're right.

    What I didn't mention is that we briefly tried a new MAF, and needless to say that made sod all difference. We're getting a refund on the MAF
     
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