Originally Posted by iiotoko
I have ~3000 miles on my Oct build e90 (330i S/P), and have noticed that the left exhaust emits considerably more black gook than the right.
Is there a specific reason for this? Is this something that I should be concerned with?
The right exhaust has a flap that opens only at higher load / revs. So when your on partial throttle (most of the time), you´re only using the left exhaust. Also there´s way moore soot buildup on partial throttle because the exhaust gases are flowing slower and there´s a less complete burning taking place in the engine.
So the effect is normal and nothing to worry about.