[cavyman]

I have my cat cut out, and a full 2.5'' exaust from the manifold back I got a check engine light on for about 2 days and the car was overfueling tailpipe was black!!, then i added a cai, and re-set the cpu (unplug the battery cable for about 15-20 minutes), I don't know if the light was an accual exaust code but it has never came on again!

oh, yeah I had a bung welded in the pipe in the same spot as the old one to put the 02 sensor in. but if yours is just hanging under the car, forget everything i said and get it put in the pipe