2004 Ford Thunderbird 3.9L Intermittent Misfire cylinder 1-8

Hello, I am new here to the Forum and have been a tech for 9 years. I rarely run into issues like this and am not sure where to start next. This vehicle came in for a misfire condition. Cylinders 1-8 stored. Performed cylinder contribution test with scanner. upon initial checks found the fuel trims -28 and found the intake was leaking. Re-sealed the intake manifold and smoke tested for leaks after repair and no leak was found. checked fuel trims and were switching at -2 to +2. Checked Fuel pressure and measured 50PSi with no drop. Replaced all 8 ignition coils with parts from dealer. Replaced 8 spark plugs (aftermarket). The ignition coils were very soft due to being saturated with oil. Replaced valve cover gaskets. Replaced PCM.

Vehicle will run great for along period of time at idle and driving. Then after about an hour or more will start to misfire, then on its own stop misfiring. I think this is indicating that the misfire occurs when hot. I also noticed that when the vehicle misfires the instrument cluster and interior lights are dimming and getting brighter and may also occur when the a/c clutch is engaged and disengaged. Faults codes: p0351:FF, P0352:ff, P0353:ff, P0354:ff, P0355:ff, P0356FF, P0357:ff, Po358:FF (Primary ignition circuit faults cylinder 1-. PLEASE HELP !! THANK YOU IN ADVANCE FOR ANY DIRECTION WITH THIS.

UPDATE: Performed relative compression test with scanner and all measured 0%. Performed cylinder contribution test and cylinder 5 measured -550 and other cylinders hovering around 0-1. This indicates to me that there is an issue with cylinder 5. Performed an RPM drop test and disconnected the ignition coil and RPM dropped and misfire condition increased significantly. Disconnected fuel injector and RPM dropped, and misfire condition increased significantly. still faults for all 8 cylinders. After engine cooled off and on a cold start I could feel a light misfire on cold start and while warm. Performed compression test on cylinder 5 and measured 155 PSI.

Those codes you have are coil primary codes. Have you current ramped the coils and injectors? I’m guessing the pcm drivers are failing when getting hot. If you don’t have a scope maybe heat the pcm up with a heat gun with the engine at room temperature and see if it misfires.

Yes this was my thought as well, but the PCM is new, Coils, and Plugs all new.

You checking to make sure you’re not losing power to all the coils? When it’s acting up. But I think your gonna have to amp clamp them to see if your losing control of them