Heres the problem- I just finished installing a full custom exhaust (3.5 inch) and headers on my supercharged 95 m3. I welded a bung for the o2 sensor as close to the original area as i could. the cats are obviously off- the first day i drove my car it was loud but great. second day- i took off and threw a check engine light! Had it checked out and the diagnostics said it was the o2 sensor. Cars got 68k on it so its about that time to change it anyways-

Heres the additional question- do you guys think that it was just coincidental or do you guys think that the placement of the o2 sensor isnt receiving enough heat? the piping is substantially larger and without the cats that exhaust doesnt retain enough heat. If i drive the car carefully and not boost for a while then i dont throw a check engine. The a/f guage i have is showing that the oxygen sensor isnt dithering as fast as it should. I am going to replace the o2 sensor asap but no one on the weekends can get em. Opinions please!!

did it get banged around at all during install or removal? they can be sensitive to shock.

nope it was fine... it was fine the first day and now its giving slow readings... hopefully it is a coincidence!

it was prob time to change it anyways. 68k is alot on an o2 sensor. i had my original one for 55k, then i replaced the second one at 92k (95m3). both gave out CE light errors.