My A4 has lately been making a lot of black smoke on relatively mild accelaration. So much so, its is becoming embarrasing as I see the smoke in the rear view mirror day and night. The strange thing is that the car (done 41K miles), drives perfectly, doesn't appear to have lost any MPG or performance and has just had a major service with new air filter. The car does a minimum of 150 motorway miles a week plus other driving so I can't see that it can be too sooted-up. Also, some days (on the same tank of fuel) it just doesn't smoke at all even if I try to make it.
What is this likely to be ? I have discounted MAF, and air filter, so could it be another valve sticking or a sensor problem of some type ?
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looking forward to a response to your post as I have similar problems, same car and engine although a few more miles! It appears particularly bad in the dark in other cars headlights. I asked my girllfriend to drive and I followed in her car and its also visible in daylight under normal acceleration - nothing when following on the motorway though at 70.
What mpg are you getting? I'm getting 45mpg on a 10 mile trip to work, combination of rural and town driving. 50-55 on a long run which I think is pretty good.
Car has just been serviced by Audi as well and the injectors have been flushed and cleaned at every service since new so hoping that rules those out.
MAF has never been changed so that was going to be my next port of call, however it doesnt have any performance issues.
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I get pretty much the same MPG as you have noted.
I elliminated the MAF by unplugging it. The car then drove really badly, when I re-connected it the car drove perfectly again.
The only other thing out of the ordinary is that when they serviced it about a month ago, the oil level is well beyond the MAX mark, could this be the reason ?
I'm surprised there are no VaG diesel experts that can comment.
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Black smoke is the result of insufficient air getting to the engine for the amount of fuel being injected.
The usual reason for this is an intake air leak between the turbo and the inlet manifold.
There are several connectors you can look at.
Turbo down to the x-member.
X-member to the intercooler. This is a tight bend and seem more likely to come loose.
Intercooler to the inlet manifold.
Other than that, get it on VAGCOM and do an acceleration run to log the sensor operation.
Rgds
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Hi Alec
With your suggestions, would you expect any performance issues? Mine seems fine, infact my Dad has just got a A4 2.0 170bhp and struggled to leave me when I was following him - plenty of smoke out of the back of his as well and its only 5 weeks old with 3K on it!!
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If you drive slowly, gently on and off the gas, like in town then floor it it will smoke for a few seconds even if everything is ok.
At night you can see smoke in the headlights of the car behind.
Does the 2.0 A4 not have a particulate filter ?
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It's most likely the EGR valve. This is a common problem on TDI's. The valve sticks. My Passat TDI had this problem. You have the same engine so it's an easy diagnose and repair.
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\"Nothing less than 8 cylinders will do\"
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An update on the original problem of the black smoke, I acquired some Forte Advanced Diesel Treatment which is not generally on sale to the public. Since then over XMAS I have done around 600 miles on the treated tankfull, the smoke is now gone, apart from some extreme driving circumstances when ANY diesel on the planet would make black smoke !
So if anyone out there has a similar problem I would recommend this stuff.
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