I just put on a new cat back and it's alot louder than I thought. My CEL / ATTS lights are on and the ECU is throwing a P0420 code: Catalyst efficiency below threshold.
If the ceramics inside my cat are broken would this cause my 5zigen exhaust to be louder than normal? Also, when i turn off the engine, I can hear loud pops and crackles coming from the converter. I'm assuming I need a new one. Will this one be okay w OBDII? http://www.mufflertech.com/htm...id=58

I've heard that high flow cats don't work well w/ OBDII. I just don't want to get a new cat and have the CEL come on again.