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2.5 tdi - smoking at low revs -no power loss...ideas ?

Discussion in 'Diesel forum' started by nicknick, Feb 27, 2009.

  1. nicknick
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    nicknick New Member

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    [Feb 27, 2009]
    Hi - my A6 has the 2.5 TDI 150BHP engine. It's done a lot of miles now (170K) and has started to smoke a little.

    It doesn't do it at start up but it's noticeable in evening traffic at sub 2k revs. Smoke is dark in colour. No loss of power - other than an occasional slight judder at around 1500 revs. It revs freely and doesn't smoke at speed -other than the to be expected smoke when flooring it. As an example - going through a 50MPH speed limit in 6th it will start to smoke heavily - drop down to 5th / 4th but maintain speed and the smoke goes.

    No codes showing in vagcom.

    Any ideas where to look -wondered if it's turbo oil seals..but the turbo has no boost problem and the smoke is not blue ?

    I wondered if it's a stuck wastegate but not sure if this car has a wastegate ?
    or if it's EGR valve sticking open ?,
    or it's N75 - but from what I read that seems to come with a drop in power so think I can discount that one.

    Best guess I have at the minute is dodgy injector - but would this explain the smoke stopping at circa 2k rpm and higher and the occasional judder at 1500 rpm ?


    I'm tempted to stick a bottle of injector cleaner in it to see if that helps ?

    Appreciate any thoughts ?
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  3. PW-Motorsport
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    PW-Motorsport Member

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    [Feb 28, 2009]
    What is the crankcase pressure like?

    Remove the oil filler cap when the engine is running, any pressure you have a blocked crankcase breather.

    The one to change is located in the V of the engine to the rear of the TDI pump. A bit of a fiddle to change £60 for the parts.

    I am sure I have a spare one here.
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  4. nicknick
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    nicknick New Member

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    [Feb 28, 2009]
    It's not the crankcase breather ..I've already replaced that twice (last time with the newer version) , and in any case the symptons are not the same ...with that I had white smoke at idle. This issue was dark grey / black smoke and was when driving with revs sub 2k.

    The fix I found was simple - a new air filter.

    I guess the old one was overdue a change and there was quite a bit of leaves and pods trapped in it which would have restricted airflow....so I think the ecu was overcompensating for lack of air with more fuel - hence the smoke.
    The judder has also gone - so I assume that was from running too rich etc.

    The car is much faster on the pickup sub 2k revs now - almost night and day difference.

    Hope this helps anyone else in the future...
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