Pre-cat sensor controls fuel mixture. Post cat sensor just tells the PCM the cat is working. If the PCM thinks the cat ISN'T working (sets a code), it will lean out the mixture some. So long as you don't see the CEL, the engine will run just the way it did when the cat was there. (only better...) If you end up getting a code, just do the non-fouler trick, there is a diy in the FAQ section on it.

 

Haha Thanks