How about the IPR?
Wires chafed & shorted on the plug?
Has the tin nut vibrated off and the coil is sliding around?
You could try "rapping" on it to dislodge a stuck pintle (worth a shot....
You can even try taking it apart and cleaning it, I have this ->
An IPR is a fairly robust yet intricate item. They are easy to service, but they can be damaged.
An IPR consists of two main parts: a pilot operated valve and an electromagnetic actuator. Each part has been known to give trouble. The electromagnetic actuator is in the end the solenoid was on. The pilot operated valve is the brown end.
To service the unit, first separate the pilot valve from the actuator. To do this, place the IPR in a vice. Then, use a sharp, good quality pipe wrench or similar tool to firmly grab the pilot valve body. (See picture). DO NOT ATTEMPT TO SQUEEZE THE PILOT VALVE BODY TIGHTLY IE IN A VICE OR IT WILL CRUSH AND BE RUINED.
A decent working pipe wrench works well. I've opened many IPRs this way without damaging any. The pilot valve slides on the inside of the body, so if it is crushed, it will stick and not work well.
Loosening the IPR
Once loose, the body will separate easily. However, there is a tiny needle in between the body and the actuator that MUST NOT BE LOST. (See IPR Disassembly Picture for a view of the pin.)
Normally this pin stays in the end of the body because of the oil that is present, but it has been known to come free. DO NOT LOSE IT.
More IPR Disassembly
Once the pilot valve is free of the actuator, disassemble the actuator by loosening the internal screw inside it. (No picture for this, just look inside where the pilot body screwed in.) It takes a big flat screwdriver to remove the internal screw, which is actually a guide for the actuator pin. (See IPR Exploded View Picture).
Once the pin and the internal screw is removed (guide actually), shake the actuator body firmly up and down several times to get the piston out.
IPR Exploded View
The IPR is now fully disassembled. It is possible to disassemble the pilot valve itself, but this takes a press and jigs to do it properly.
Three things commonly go wrong with the IPR:
a) debris in the pilot valve
Using a small screwdriver, gently push in on the end of the pilot valve assembly. You should feel the valve move about 1/8" in and out and return to its seat with a bit of snap. Should the action of the valve be sticky at any point, use a combination of solvent, screwdriver motion and compressed air to clear any debris that may be trapped in its motion.
Operating the IPR
b) debris in the actuator piston area
Thoroughly clean the actuator body, piston, guide and pin. Lubricate them well with a very thin oil or solvent. Assemble the actuator only, but do not tighten. With the solvent as the lubricant, the piston should move freely. I.E. if you shake the actuator assembly, you should hear the piston sliding around freely. This will not happen with motor oil as the lubricant.
c) bad external O Rings.
Examine for wear/damage. There should be a backup ring and an O Ring. The backup ring should be nearest the actuator. Ford sells a rebuild kit consisting of the O Rings and a replacement solenoid nut.
Assemble the actuator end of things. Gently tighten the internal screw (guide). Don't over tighten this. It is difficult to describe how much torque it takes. A little more than the amount for a screw in a computer case.
Place the pilot valve needle in the body. Screw the pilot valve body into the actuator body. Tighten, but don't over do it.
Reverse of removal. Tighten, but don't over tighten the IPR nut.
NOTE: A PSD WILL RUN INCREDIBLY ROUGH IF THE IPR NUT IS LOOSE. The symptoms of this will make you think you've got multiple bad injectors among other things. You might want to check it for tightness after a few hours of use.
BTW: Ford says that IPRs are not serviceable. They don't/won't service them. They rarely give trouble except for debris build up in the valve or actuator."