I just installed a 3" single apexi n1 supra TT exhaust on my Sc3 about 1.5 weeks ago. Everything was going great, sounded awsome, resonated like a banshee, but it is now very very mellow, almost normal sounding. In the begining it would blow out some black smoke at high rpms. I thought that maybe the sound change was in my head, but my friends agree and i have been experiencing a gradual loss in power. Right now my car feels slower than it did with the stock exhaust, but when i first installed the exhaust, it was very peppy, probably a 10hp gain. Feels like an overall 20hp loss now. Adding to this, my CEL went on today and the car sporatically stalls at stoplights.

Possiblity 1: My cat went bad
Possiblity 2: my o2 sensors went bad (which i dont think so since there are no o2 sensors on exhaust from the cat back)
Possibly 3: something else...

What do you guys think. Should i try and gut out my cat this week? Suggestions?

 

...hello....

 

my cat died once...

 

Cat/O2 sensor failure - Things to look into