4.0L SOHC misfire cylinder 1 p0301 & 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?

 

[2000StreetRod]

injection?

If the misfire is always on cylinder #1 then you should be able to eliminate things that would affect more than one cylinder: clogged cat, low fuel pressure, vacuum leak, incorrect camshaft timing, MAF sensor, TPS, ECT sensor, IAC valve, O2 sensors, crankshaft position sensor, EGR. That leaves compression (which you've checked), ignition (you've replaced coil pack, plug wire & plug) and injector (which you've checked and swapped).

Frankly, I'm at a loss to explain the misfire. One possibility is a block in the fuel rail (but only to #1 injector).

Since piston #1 position is used by the PCM to determine ignition and injector timing there is more importance placed on it than the other pistons. You might try cleaning the crankshaft position sensor connector by disconnecting and reconnecting it a few times.

 

[Dave 1955]

I think streetrod is on to something..sage advice!

 

[99__Explorer]

Thanks. Its worth a shot. I'll let you know what happens.