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Discussion Starter · #1 ·
Hello all,

I don't think this is anything major, but my mk1 1.6 puffs out a bit of black smoke under heavy acceleration. Under normal driving it is fine, no smoke at all.

The smoke smells like fuel, and as black smoke typically indicates fuel in the exhaust gases I figure the car might be overfuelling? But I don't know these cars well at all so am asking the experts here for a few pointers please

Since I noticed it, I have:

Changed Oil (10W-40) / Oil Filter
Changed Air Filter
Changed Spark plugs (NGK BKR6E11)

The car drives fine, no misfires and power feels like it is being delivered ok!

What should I do next?

Thanks in advance,

8,007 Posts
it does sound like its overfuelling, when the pipework from my airflow meter to the intercooler came adrift I had plumes of black smoke behind me and the car was very much down on power, half the metered air was escaping but the ecu didn't know this and so was still adding the same amount of fuel as before.

If you have the stock intake system it may be worth checking the connections from the airflow meter to the throttle body, in particular the join on the plastic crossover pipe where it has that "concertina" effect going on.

Otherwise you could try the oxygen sensor, that could be causing the symptoms iirc.

5's run rich as stock anyway, so if it's not a big problem then it may just be that.
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