Black Smoke from Exhaust diagnosed as Carbon Build up!

[jhw]

I wonder if anyone can offer some advice?

I have ‘ Black Smoke ‘emanating from the both banks of my exhaust when HOT.

I notice this mainly in the dark when I accelerate hard and it appears like a diesel car exhaust smoke. I have also passed people on motorway (80 mph in 6th gear) and they have reported smoke.

My RS4 has done 16,500 miles and has a Miltek Exhaust (Cat Back non res), the car is not thrashed when cold and was run in properly (to Audi instructions).

I am also burning a fair amount of oil, approx 1/2 litre every 1500 / 2000 miles.

I have taken it to the dealership, they can reproduce the problem, and have stated that there are no error codes visible> The dealership have been in dialogue with Audi Technical in Milton Keynes and I have escalated this to Customer Services.

The car has been with the dealership 2 weeks.

I have now been told that the Master Tech has take off the exhaust where it joins the miltek and has discovered carbon build-up which they are now saying is the cause of the smoke from exhausts (i.e. it is carbon dust not smoke). They reason for this is I do a lot of town driving (which I do not believe to be true)

Although I am very very sceptical that the smoke is carbon, I would like to know if there is a way to test smoke from the exhaust to see if there is oil in it? Or is there another way to help diagnose the problem and convince Audi to start taking the issue a little more seriously?

The carbon theory only works if I am seeing the smoke initially when the car is driven, but I see it every time I accelerate even if I have been driving a number of hours, I would expect any carbon to be blown out by then so problem would be only on initial acceleration if it was carbon!!

Any help or suggestion would be gratefully received.

Jeff

[P_G]

I've also noted with my local dealer that my OEM RS4 smokes, particularly under hard acceleration. I was advised it was rich fueling.

[Dom81]

I do mostly town driving - more's the pity.

I've never noticed any smoke when hot, and certainly not motorway 6th, but when I nail it in second that's a different matter. Obviously depends on how long since the last blast, but I can do anything from puff of smoke to nuclear winter. I find the rev limiter adds a little extra drama as well - bit like the final burst at a firework display

I've always assumed it's carbon, but will ask them to have a check at first service...

[richardofthesun]

Hi JHW
Try www.kittiwake.com, they do some excellent "lower" cost analysis kits for fuel, oils, water, etc (lower cost rather than sending a sample to ITS, Caleb Brett, LGC, etc. whom are all rather expensive, but you will get a comprehensive breakdown analysis). Not sure if Kittiwake do the exhaust side, but ask to speak to Chris Lee Jones (owner), he will be able to give you some good advice.

[mattysupra]

this dont sound correct. Black is normally over fuel. Blue is normally oil burn. To be able to see your own smoke on the motorway is never correct. Could do with a video behind the car while giving it some or something to see just how much smoke there is!

[pippyrips]

I have noticed similar symptoms with mine. Not to the point where i can see smoke in daylight however at night when cars behind have their lights i do notice a trail in my wake on occasions. After reading of some many others doing the same i have just assumed its a feature of the car?

The exhausts also blacken up quickly though its worth noting most of my journeys are short which fits in with the carbon theory above. The car has been serviced recently and came back with a clean bill of heath.

[tartan_rob]

I get the same, at night, 2nd gear say, nail it and it looks like a diesel through the lights of cars behind me. However, it looks much worse in the mirror than in reality. I do motorway miles and do not notice it on the motorway. For me I am 90% sure it is over-fuelling. I use 1/2l oil at most evry few months.

[Ozrs4]

I have seen black puff of smoke too when hitting the rev limiter in 2nd gear and was told by Audi tech that's normal. It's just over-fueling and nothing to be concerned. Other than that, I haven't noticed any smoke on highway driving in 5th or 6th gear overtaking someone. Blue smoke is more of a concern, not white or black.

[MrM]

My car smokes every journey, but only during the first time I floor it to the redline in,say, second.After that it's fine no matter how hard or gently I drive. I remember reading somewhere that the FSI engine produces as much smoke/soot as a diesel.

[PetrolDave]

I remember reading somewhere that the FSI engine produces
as much smoke/soot as a diesel.

IIRC that was on AudiWorld.

I get a puff of black smoke (soot?) when I hit the rev limiter, noticeably worse since the 0050 to 0080 engine ECU SW upgrade which has definitely made the fuelling richer (my mpg has dropped by about 2mpg since the upgrade was done).

Seems to be normal behaviour for an over-fuelled FSI engine. I'm not burning any oil so I'm not losing any sleep over it!

[audijohn]

I remember reading somewhere that the FSI engine produces as much smoke/soot as a diesel.

Yep this is correct due to the very high injection pressures in the FSI engines (as diesels) a carbon burn off results, it may be seen at night but should not be seen through the day, Oil consumption is nothing to do with it though.

[jhw]

Thank you for all the input, I will update with Audi's further diagnostics.

Jeff

[SR71]

I've just realised that maybe the smoking on cold start up is related to the FSI over-fuelling for the first few minutes....

Thats the only time my car smokes and even then it does not do it consistently...