#2 and #6 dropping rpms
I've been having a engine misfire, which almost sounds like low rpm/idle detonation with a popping through the exhaust and couldn't narrow it down to anything specific, so I brought it in to Ford so they could run a WDS. The power balance test showed that cylinders 2/6 (companion cylinders off the coil pack) are dropping severely with load. (with the most severe drop of 75 rpms between 1600-1800 rpms) Spark duration is similar on all cylinders, compression is very good and fuel pressure and leakdown is ok. All basic sensors checked out ok, BARO PID is ok at 156.5HZ, and verified PCM is coordinating fuel and injectors OK. Verified synchronization of Cam and Crank, OK.
Possible causes include coil pack or related ignition on companion cylinders 2 and 6, or internal mechanical faults such as valve train sticking/flow issues, cam profile/lifter issues, intake or exhaust manifold pressure reversions.
Replaced coil pack, plugs and wires, new set of heads, rockers and pushrods, cam and lifters checked out fine. Compression test showed 200 psi across all cylinders. I doubt this is mechanical. I have a different PCM to try out but I couldn't link up to disable the PATS because of the VIN lock on the 9100. I am waiting on that to be cleared to check if it's a faulty PCM.
I am open to ideas, opinions and suggestions as to what the cause could be, and anything else I could check out while waiting on the flasher. Is it possible that the EDIS (which is integrated into the PCM) could go bad in a way that it only affects 2 cylinders? Any help would be appreciated.