Does your scan tool show which individual cylinder is misfiring? I think OBD2 has that capability...

BTW, if you dropped any plugs during installation, that becomes a suspect.

 

After I installed the RT Y pipe, I could definitely hear a misfire and it would get worse under load. After replacing the bad O2, the misfire, and the PO300 code, stopped.

There is no real way to check if the O2 is bad, unless you are getting a bank specific code. If you are getting a bank specific code, you can swap the front O2s and see if the code changes banks.

Good luck,
Thomas.

 

I replaced both upstream 02 sensors with new ones and also replaced a leaking drivers side header collector gasket. Still have the 0300 DTC miss. The miss seems more obvious when in closed loop. Not sure where to go from here......

 

Make sure you don't have any exhaust leaks at the y-pipe. Test the plug wires.

 

Turns out it was the dang #2 spark plug; I must have bent the electode when installing it because it was gapped around .005. That number 2 cylinder is a pain in the **** when you have SLP shorties and the darn air pump crap in the way. Oh well, I'm a happy camper again....