Exhaust fumes in cockpit

[DamianURS4]

Chaps,

As the title reads - the Avant suffers periodically from fumes in the rear. Its intermittent, there are no cracks in the exhaust or the EM so no visible smoke in the engine bay as far as I know. Odd that it only occurs in the rear, and it leaves me to wonder whether it is getting into the vents that exit under the front seats.

Any pointers/ advice????

[sam80quattro]

valve stem oil seals or split breather pipes could be the cause, many miles on it?

[rj scotty]

check the seal that separates the engine compartment from the air intake/fuse box/wiper section.
Mines always coming loose and fumes then enter the cockpit.

[DamianURS4]

TBH the cover that seperates the air intake box and the engine compartment is shot - so its looking very likely -
head recently replaced with 7A uprated unit so internals are safe AKAIK......

Will look further - thanks so far.

[DamianURS4]

ok, the fumes are entering through the back of the car = perhaps through the boot seal etc - I am not sure if certain behaviour contributes to this however I have my suspicions that it occurs when I am coasting or easing off...... I have a spare bootlid and can transplant the trim from donor car but only if i have a modicum of confidence in the results......my neighbour has a garage and has mentioned the possibility of passing coloured smoke outside the car on a ramp to see if it is leaking in to the car.....

Has anyone been down this road before?

[Nuvo]

I would check the vent trims at either side of the car, they are at left and right hand sides of the rear bumper (behind the bumper).
Each vent has a little flap which opens to let a build up of exhaust fumes escape. I would check the condition of these flaps.

[driftin jo]

ok, the fumes are entering through the back of the car = perhaps through the boot seal etc - I am not sure if certain behaviour contributes to this however I have my suspicions that it occurs when I am coasting or easing off...... I have a spare bootlid and can transplant the trim from donor car but only if i have a modicum of confidence in the results......my neighbour has a garage and has mentioned the possibility of passing coloured smoke outside the car on a ramp to see if it is leaking in to the car.....

Has anyone been down this road before?

It could well be the tail gate seal, the back of the car is a low pressure zone and exhaust will be drawn in if it can be , you also mentioned that it does it more when you are easing off, this makes sense as the exhaust gas speed exiting the tail pipe is slow and thus it cannot then escape the low
pressure zone at the rear of the car and is drawn in.

[Costash]

I think I have the same problem Any updates?

[newsh]

I have this problem too, it happens when I have the windows open. I've had the rear bumper off and discovered that one of my vents was broken I taped it over with gaffa tape but have another one to fit (these vents should get sucked closed when there's a vacuum in the car). Anyway its still doing it at the mo. My theory is that when I open the window the pressure in the car drops and the fumes are sucked in through the back of the car. The tailgate seal looks ok and the remaining vent seems to work. I never get the fumes when the windows are closed and the fan is blowing.

Its definitely worth having the bumper off and checking those vents to make sure the little rubber flaps are sitting right and they seal properly.

[spink]

I have this problem too, it happens when I have the windows open.

same here on my a6

[Acidburn]

from experience i'd say its the vents behind the rear bumper, had this before.

[newsh]

Might have to buy new ones then...

[Acidburn]

Might have to buy new ones then...

if they are the same as a coupe i've got a few.

[newsh]

Avant ones are different

[newsh]

Think I've sussed this guys

Took the bumper off to have another look and replace the near side vent. The gaffa I'd put over the hole was still in place so no way fumes could have been getting in that way. Before clipping the vent into place I had a poke around in the cavity behind it and noticed there was a gap in the back corner, there are some blocks of foam in there to seal off the space but because of the gap I could put my fingers through into the space where the bumper bracket goes in. So there was quite a big leak straight through just above the exhaust.
I cut some blocks of that heavy duty particle foam and squeezed them into place from the vent aperture. I then doubled it up by working foam into the gaps all round the bumper bracket (in my case the towbar bracket too) I've got my bumper set up so it just slips onto the bolts and secures at the arches, saves having to take the boot lining off to remove it...
I'm just doing a repair on the RH bumper bracket again and then I'll take it for a test drive. Might leave the bumper off till tonight and check with a torch for any more leaks.
The best way to hit this problem if you want to do it without removing the vents would be to remove the bumper and just plug the 2 holes where the brackets mount with foam. Not sure if these have been left open on mine when the tow bar was fitted or the car has always been like it.
Hopefully this is now sealed and the fumes will stop.