about a month ago i put a 3 inch atp testpipe with 2.5 inch tectonics downpipe with 2.5inch piping w/o resonator with a magnaflow muffler. before i had no check engine light on and spiked at 20 psi. well now because of the testpipe there is a check engine light from the o2 sensor i think. the car does not pust over 15psi. could that cause the problem?

 

dunno doesnt seem right at all I had the same set up exhaust wise but with GIAC and never had any problems did you do the non-fouler mod on the TP??

 

Do the non-fouler mod if you haven't already. The cel might be from something else. The problem shouldn't be because of the bigger pipe (unless you went to like 8" exhaust).