A6 C6 Allroad 3.0 tdi fumes

[mhobson]

That seems like a reasonable idea, I have looked and listened for leaks with the bonnet open and engine running but found none and have never found fumes as strong under the bonnet as strong as arrive through the vents. The other mystery is if the fumes were coming from the engine compartment, how are they getting into the heater intake, I can find no obvious opening, nevertheless I am suspicious about the EGR system and think I may try taking it apart to see if there are issues, but I can see not carbon or burnt oil, it looks like a very clean engine.

[lynalldiscovery]

Can you not get someone with a smoke testing machine to pressurise the exhaust system to see where the crack is? not an mot smoke testing machine but the one that makes smoke to test for leaks in pipework and turbo ducting etc

[Tich52]

Did you ever find a resolution to this problem? My A6 Avant 3.0tdi has exactly the same problem. Thanks.

[mhobson]

No I never found the fault, intermittent faults are, of course, very difficult to find, I could drive for 3 weeks, no problem, then it would happen maybe 3 times in one day. To me the smell is of crankcase fumes, it is very much stronger than normal exhaust fumes. I read that when injectors are worn and overfuelling, much of the excess can pass the pistons causing a dilution and increase in level of engine oil. My oil level had been rising so I changed the injectors, all went well for a while and the fumes came back but still only occasionally, the car drove much better though with definitely more power. I put an extra seal under the bonnet to reduce the possibility of engine fumes getting into the A/C. The only remaining possibility in my view is that fumes are coming from underneath and entering the plenum chamber from below, maybe through the water drain holes, if you solve it let me know. Regards, Michael

[chilledgibbo]

I had similar and it was two of the injectors which had had blow by issues due to poor seating, leading to small lumps of tar gunking up around the bad injectors.

[mhobson]

Thank you for that, but I changed all of the injectors myself since the problem arose and no change.

I suspect the fault is with the flexible exhaust pipes, one maybe being split, there is one each side of the engine and one taking boost to the turbo. The flexibles are there to cope with engine twist, it twists one way on acceleration and the other way when decelerating in gear. Finding which way may be faulty would need to be able to twist the engine while it is running, which I am not able to do and to replace all three would not be cheap. I have viewed from underneath with the engine running and could not find a leak. Maybe a professional with a fume sensor may be able to find it.