A6 C6 Allroad 3.0 tdi fumes

[swalker]

Straight away I thought injectors or cracked/blown manifold gasket, was nearly sick when i lifted washer bottle cap and took a deep sniff, cheapest fix ever!

I would agree but asking for help and being narrow minded seems to be in order here.

[mhobson]

I am asking for help and hope you do not think I am narrow minded, there is no doubt that they are crankcase fumes and that they are definitely coming from the air vents upon deceleration. I do not know much about the EGR system on this car, thought the problem was where the gases return in a hose just before the turbo where there had been signs of a leak, oil and carbon, but when the turbo was replaced that leak was fixed but the problem remains, and even then I had thought that the seal between the underside of the bonnet and engine bulkhead would keep the air clean. Now there are no visible leaks on the EGR system nor stored engine fault codes nor audible leaks on the exhaust. I do not know where to go from here.

[lynalldiscovery]

Im not familiar with the breather system accept know like most modern cars its a closed loop jobby, so if you can smell it there has to be a split in the pipework somewhere.
Are all the bonnet sealing rubbers still there including the one between engine and the brake cylinder section?

[lynalldiscovery]

Just google searching on here and interesting reply from Crasher saying if someone has removed the plenum drain bungs, any fumes can get up into the heater intake and said one of the better quality active cabin filters might help, could be a cheap fix?

[mhobson]

The air intake is at the side of the blower box which is situated in a compartment in front of the windscreen but behind the engine along with the hydraulic reservoir. This compartment is supposedly sealed from the engine compartment by a long rubber seal. I have augmented this rubber seal with a special high density foam which I have glued to the underside of the bonnet, inspecting this foam seal after some mileage you can see that it is slightly squashed where it rests on the rubber seal so it is definitely making good contact. The smell is definitely not hydralic fluid. The engine on this car runs clean, if you stand behind it with the engine running it is not offensive, I have a diesel Sprinter van, the smell is exactly the same as the van exhaust when the engine is cold. I do not know where the plenum drain bungs are or how you remove them or how they are associated with this problem. On my last service I changed the A/C filter with an active filter but I cannot remember the make.

[lynalldiscovery]

The drain bungs basically let any water out that gets into the chamber, sadly they block up and the chamber becomes a pond causing all sorts of aggro, so very common to pop them out/through the hole in the steel work so theres never any chance of water getting trapped, the hole left when the bung is removed os quite large at least an inch in diameter, the underside of the holes is pretty much over the gearbox/rear of engine area so possible for fumes to come back up theses holes at a standstill.
Ive done three of the wifes audis now and it is always one of the first things on my hit list, a decent torch and a keen eye can spot the bungs, Im sure google will chuck you some images?

[mhobson]

Thank you very much for that I will have to see if I can find them, however I never get the fumes when the car is stationary, only when I am slowing down from a steady run, if after suffering fumes and the car stops, the fumes clear reasonably quickly, I will check out some images, thanke again.

[lynalldiscovery]

Had another thought and this relates to all the landrovers Ive owned over the years and the thought is in the back normally either side of the 3rd rows seats hidden away behind trim are vent flaps made from thin rubber that let air out and not in, thinking maybe as yours is an estate it has something along the same lines and they have failed, been missed off during repairs etc?

[mhobson]

Firstly the odour is coming directly from the air vents and it is much stronger than pure exhaust fumes. I have looked on Google and Youtube and although there are sometimes faults with the rain drains either side of the the A/C section the bockage of which can cause footwell flooding, I cannot find plenum grommets anywhere nor can I find any Audi listing for the parts. I am wondering if this particular system does not have them in the plenum chamber because I have found that there is a special drain moulding connected to the unit which funnels away rain water from the fan unit, Audi part number for RHD vehicles is: 4F2819979A. I may have a grovel underneath today with my torch and see if I can find anything.

[bluezie]

If this is only happening on deceleration, it sounds like there is a crack or split in the exhaust / EGR or breather system that only opens up and leaks when the engine tips forward during deceleration. It may not show any easy to see signs of soot or oil if it's not leaking all the time.