I have aprox 18k miles on my L, in just under a year I've had it. Exaust tip has always been black, inside it. I brought it to the studio once ]for this. They only indicated the air fuel mixture was in specs. Tought for me to accept that, based on the test only. The performance is great. The fuel consumption is good. Although, purely city driving,, can average as low as 17-18 mpg at times. Now, since this is my first turbo vehicle, is it possible, that air fuel, goes rich each time the vehicle enters boost? I have no clue. However, I just wonder, if any of you have sooty looking inside exhaust tip...on every previous vehicle I've owned, I've only had light grey in exaust tip. No soot. If some of you could give me your opinion, on this. Especially if you find a sooty, black inside exaust tip.