Ok so I finally got my LQ9 swapped in (tune, headers, Roller Rockers, Cam-not big- NGK TR55s MSD Wires, Got it going after fighting with the Harland Sharps to get them to fit and noticed it was really running rich (open headers) like rich enough that it made me cry when I was topping off the trans. After It warmed up the ses light started flashing. 1. Checked Compression 175psi. 2. Noticed one plug wire was a little off pushed it back on and it seemed to make it better but still misses a little, what should I do next on my quest to find the miss?

 

Open headers.. Where are the O2's mounted?
Code is?
Scan/data logs available?
Once warm closed loop came in and the O2 readings are causing the fat condition, would be my guess.

 

It still has the stock 5.3 y-pipe loosely bolted up untill I can get it to the muffler shop, its like 1/4 inch gap to help keep down the noise from initial start up and the 02's are still in stock locations. Its got a tune so I dont get any codes now but it used to get random missfire codes before the tune. I think I am leaning towards a bad 02 sensor, pulled the plugs today: drivers side looked normal and the pass side were black as coal and sooty.

 

try throwing some plugs in it and running it open loop(gently) until you get the exhaust buttoned up.

 

new exhaust put on and 1 new 02 sensor now its running great!

 

Sounds like ur tune is lacking tune.

 

the tune was done by Nelson's Performance so I know its not the tune, it was on my end of getting the truck together. (probably knocked around that O2 when removing the exhaust)