Hey guys, I just recently put in a zzp mid length header and downpipe in my car (06 sc). When I went out to test drive it I noticed that its lacking power at upper rpms (around 5500 to redline). It kinda feels like I'm hitting a fuel cutoff cause the engine feels like its stuttering. Boost goes up to about 13 psi bit then starts dipping to around 10.5. Does anyone have a clue what this is? I'm guessing my oxygen sensor may have got messed up while installing. Also, whine the engine is running I have no check engine light, but when I shut the engine off and leave the ignition on, the check engine light stays on.

My wife has my obdII scanner in her car, once she gets back from work I'll scan the cobalt

 

The CEL is supposed to stay on if the key is in but engine off

 

I understand that, but after I start the engine there's no cel...I have never seen a car do that

 

No what he's saying is if you have your key in the "run" position with the engine off, the CEL will be on no matter what. Everyone's Cobalt does this.

 

Yes, thanks. My guess is they do it to show emissions testers that the light does in fact work.

 

Ahhh, gotcha read it wrong

 

Could be a fouled O2 sensor, could also be your knock sensor. The last track day i was at my car locked itself out at 4100rpm and was running stupid rich due to a combo of tune corruption and the knock sensor freaking out and false positiving over the SC rotors.