I hope it's not bad etiquette to jump in on a thread but I have a similar problem. Just finished reinstalling the engine on my G8 GT after DoD delete (and other work.) I actually missed two grounds when I was hooking the wiring harness back up - the big ground from the ECM to the ground stud on the front of the right head and the coil ground for the left bank coils on the back of the left head. Without the ECM ground connected, of course, the engine wouldn't even crank. (I think that I should have gotten a P0606 code at this point but I didn't.) After I found and connected the ECM ground, the engine started and, believe it or not, ran with good spark on 2 and 8 and intermittent spark on 4 and 6. Found and connected the ground for the left bank coils and thought all would be fine. Not quite. At that point,#2 & #4 coils were not firing at all and I suspect (because of exhaust manifold temps) that others are firing intermittently. After reading this thread, I carefully cleaned the contacts for the 4 pin coil connectors and the 7 pin connector. I have good grounds on both the A and B pins on the connectors for #2 and #4 coils. However, I still have no spark on #2 and only intermittent spark on #4 (which is at least a slight improvement.) Interestingly, I'm not getting a misfire code (P0301 thru 0308, I think) and I'm not getting an Ignition Coil Control Circuit failure code (P0351-0357). I think that my code reader is working and communicating with the ECM because I'm getting that pesky P0449 Emissions Purge Valve code that I just can't seem to eliminate.
Which pin on the 4-pin connector supplies the voltage to fire the coil and how would I check for proper voltage? BTW, I did order another coil just on the off chance that the #2 coil could have somehow gone bad in this process. Worst case scenario, the old coil will not be the problem and I'll have a spare. Hopefully, I'll know tomorrow.
Thanks in advance for your help.