Ive noticed that the tips of my exhaust tips are black on my 01 s4. I try to scrub them clean every time that I wash the car. Is this a sign of the car running rich or lean? I do not know how to tell. I have an oct ecu. Or is this just normal with the car?
Also, I noticed that when I rev the car, there sometimes is a "patch" when I blip the throttle. Is this something to worry about? possible misfire? I am not getting any lights on the dash.

rich it is pretty normal, what kind exhaust are you running?


mine backfires all the time, but i am runing nothing till the muffler

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S4 bumper in my basement awaiting paint

Thats normal, now if you blowing black smoke all the time then you have a problem. Sometimes you will get a little smoke when you floor it, its probly just a little oil blow by burning up.

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2000 S4 Brilliant Black- APR R1 DV, Borla Cat-Back, H&R Adj. Coilovers, CC Mod, Pioneer AVIC D3, GIAC! Stage 3- Soon!

I'm still on the stock exhaust. I drove the car for 6 months and i thought I had the stock ecu in the car until I opened up the box one day. Is that hard on the engine when it backfires?

Backfires are not bad for your car usually its justbad timing, or your car running a little lean.

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2000 S4 Brilliant Black- APR R1 DV, Borla Cat-Back, H&R Adj. Coilovers, CC Mod, Pioneer AVIC D3, GIAC! Stage 3- Soon!

mine does it when the idle settles real quick, either after just coming from high rpms, or starting to take off then having to stop quick

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S4 bumper in my basement awaiting paint

http://en.wikipedia.org/wiki/Back-fire

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S4 bumper in my basement awaiting paint

thanks for thehelp guys.