4.0L SOHC misfire cylinder 1 and rough idle

[99__Explorer]

I'm having a problem with my 99 Explorer 4.0L SOHC, misfire in cylinder 1 p0301 and can't seem to figure out the problem. Truck has 154k and a rough idle and bad acceleration. I've checked and tried everything I can think of so I looking for a little help here.

Ignition system seems to be okay. It has new motorcraft plugs gap to spec, new wires ohm out to spec, and a new coil pack also ohm out to spec. I've also tried swaping plugs from different cylinders, no change.

I've checked the compression on a few of the cylinders, all are within 10psi of each other. Cylinder 1 leakdown test passed.

Fuel system seems to be working. Injectors ohm out to spec and are all close in ohms. I've swapped injectors 1 and 2 no change. I'm getting power to injector electrical plug from the PCM (test light flashes when cranking engine).

I've checked for vacuum leaks and found none. I replaced the upper & lower intake manifold gaskets to be safe, no change. Vacuum lines not leaking. Throttle body and intake cleaned and checked over seem to be okay.

I've tired blocking off EGR no change. IAC motor cleaned and tested fine. MAF cleaned, voltage readings good. Throttle plate cleaned and TPS sensor tests good.

The only thing I can think of is maybe a faulty PCM setting. Any ideas?

 

[arco777]

Have you tried swapping the #1 plug out, maybe moving to another cylinder? I had issues with Motorcraft plugs getting hairline cracks in them and causing misfires. In under 10,000 miles three of them failed in this manner.