I am working on replacing my O2 sensor. When I pulled the old one out I discovered that it has a black sooty deposit on it. A powdery sort of black soot. I am concerned about what could cause this. I believe that this sort of deposit is indicative of a rich running condition.

I have no check engine light. The sensor does seem to be sluggish, which is why I am replacing it. After seeing it now I know why.

Do you think this is a sympton of the sensor itself going bad and causing a rich condition? Or do you think I have some other problem? Car has 108K. FPR is new. Coolant temp sensor is new. (That failed with a check engine light last year). Last year I also put in a whole new exhaust from headpipe to tailpipe. I don't remember the sensor looking so bad then, but I didn't exactly study it. Gas mileage seems low. 19mpg around town and 20-21 highway.

I installed my new O2 sensor, went to plug in the cable (direct fit replacement) and discovered that it is 2 feet too short. ARGHHHHH! I cleaned up the old sensor with a copper brush and put back in until I can get a new sensor.

Thanks all.