Hey Guys , new to the forum. Just recently acquired a 07 Cobalt SS. From what i have read the stock boost pressures are roughly 12 PSI MAX. Someone correct me on anything if i am wrong , this is my first ownership of a LSJ but i have worked on 2 others that buddies have had. My problem is that i thought i bought a pretty much stock car. The only things known to be done to it is a shorty ZZP header , and a unmarked CAI. At idle it has what sounds like a small misfire , it also misses 3 or 4 times between 5,000 - 6,500 RPM at WOT. I didnt notice until today that when i was doing a pull in 3rd that i glanced over at the boost gauge and it was sitting at 16 PSI right before redline where it fell off and came back down roughly to 13 PSI at 6,500. Like i said i remember working on a couple other buddies LSJ Cobalt's and they seemed to sit between 10 and 12 PSI stock so i was alarmed to see anything higher than that.
I have checked and it has a 3+3/4" pulley that looks stock and pressed onto the S/C Shaft. Stock crank pulley so it doesn't have an Overdrive pulley system on it. The alternator and idler pulleys seem to look normal. So i cant tell where this boost pressure is coming from IF INDEED it is actually running 16PSI and not just a faulty gauge. It does look to still have the stock Lime green injectors in it so i was wondering if it had a Lean misfire since its running so much more air. Any and all help would be appreciated!!! Definitely do not like making my first forum entrance issue related haha.

 

Does it still have a cat?

 

yes sir it does , full stock exhaust besides the shorty header

 

Then your cat may be getting plugged.

 

That might explain why the car had a blowed header gasket and a blown mid pipe muffler gasket when I bought it ... ...

 

One of the easiest way to tell if you have a clogged cat is to take it out at night, beat the **** out of it, pull over, and try to get a look at the catalytic converter. If it's glowing red... it's clogged.

This was a fairly common occurrence on LSJ's, from what I remember.