I have been chasing misfires for a couple of weeks on a friend's 06 GTO. The mods are 228/238 cam, PRC 243 heads, Kooks 1 3/4 LTs, Corsa, FMS green tops, vic jr, edelbrock elbow and vara-ram. He also recently went with a Spec 3 and aluminum flywheel.
The symptom is misfires predominately on cyl 5 and 6. As much at 2500+ depending on how long I drive it, where as the other cylinders are anywhere from 0-15. The weird thing is it only misfires above 2k rpms. I can drive all day under 2k but as soon as I cruise over 2k the misfires rack up.
We have switch coils, switched plug wires, gapped and regapped the plugs, injectors are 2 wks old. I have been adjusting the timing back and forth in the 2k to 2400 rpm cells with no improvement. I was thinking the timing was too far retarded and causing the misfire. I have looked over the CPS wiring and found nothing.
I have attached the tune, and logs. The only thing I have left to check is two swap injectors around and see if they problem follows the injector. The other thing I was thinking is the aluminum flywheel is throwing everything off