2009 Pontiac G8 GT 6.0L Engine P0306 Fault: Check Engine Light On, Rough Idle After Stop
The vehicle was running smoothly on the way home until it stopped at a traffic light. At that point, the check engine light illuminated and the engine began running roughly. I checked cylinder #6 compression and found it to be 150 psi. I replaced the spark plugs, wires, and coil packs, and performed a vacuum leak inspection as well as checks for faulty valve springs or rockers. The check engine light remained on, and upon retesting, the spark plug in cylinder #6 was still wet with fuel, despite the P0306 code persisting. The engine continues to run roughly. I'm seeking advice on how to resolve this issue. Any insights would be greatly appreciated.
First, confirm that cylinder #6 is actually firing. The vehicle is stock with only AC Delco components. Coil connector issues are known in this model. If cylinder #6 isn't firing, we can inspect the wiring directly. Additionally, use a noid light to check if the fuel injector for cylinder #6 is receiving power. A fuel pressure test and a KOEO leak-down test would help identify any faulty injectors or internal leaks.