Okay so here's the deal.

I picked up some more parts from my buddy who has an '03 coupe. He gave me the mid-pipe he had, but he had the cat cut off and put on a straight pipe. Will running without a cat mess up the rear bumper of my car? I've seen plenty of cars with that black soot residue on their back bumpers and I don't want that on my car.

Also, how will that affect o2 sensors and the CEL? The CEL is currently on for the o2 sensors, which I was going to replace when I changed out the midpipe.

Thoughts?