2003 F150 PCM going bad
 

PCM, coil "a", and AC clutch, keep failing at the same time. Traced wires, found no problems. Truck runs, but only on 7 cylinders.

What are you working on?

Working on a 2003 F150 5.4L engine. Replaced computer, ran good for 2 days, then went bad again.

Sounds like a short someplace.

Could it be the AC clutch itself, I traced the wires from the coils to the PCM and found no problems. The truck ran good for a whole day before it went bad again. Now, as soon as I start it, it blows up coil A. (#1 cylinder). It runs good, but only on 7 cylinders.

Are you sure it's a coil failure? Have you swapped coils with another cylinder to see? What is the compression in that cylinder?

What exactly do you mean by "blows up coil A"?

Did you verify that the clutch coil diode is present and good? It's there to absorb the transient (surge) when the clutch de-energizes.

Coil A just blows up. Takes ten seconds after engine starts, then it blows up, literally.

Is the clutch diode right there next to coil A? I don't know. Connection looks corroded.

If it were the clutch diode, would I need to replace the PCM again, or just the bad coil and the diode? I mean, can a bad a clutch diode also damage the PCM, or just coil A?