Okay where to start here.. I have a 94 Jeep Cherokee 4.0l HO with an auto tranny. My original motor I had in it, the rings were shot, it was blowing some smoke and going through some oil. Well I stumbled into a deal at the local salvage yard for a used motor from a jeep that I can hear it run first before they pull it for only $100, they even pulled it for me. Well long story short, after a long day and a half, I pulled my motor with some friends, dropped the used motor in, was trying to start it with no luck, until out of nowhere, from what we thought was a backfire, the bolts that go into the block for the engine mount bracket snapped. And not just the bolts snapped, the entire block where the bolts go did as well, how this happened I do not know. Well I returned the motor and decided to do a full rebuild. Well pistons, rings, bearings, camshaft, lifters, gaskets, seals, etc, all that later, we drop it in, and still will not start. I have great fuel pressure at the rail, timing chain is dead on, timing on distributor is dead on, I have spark to all 6 plugs. Ive tried multiple camshaft sensors and crank position sensors, CTS, TPS, IAC, Oxygen and MAP sensors. The problem is, there is no voltage at the injectors, therefore they are not pulsing. Ive came across a few things, when the key is in the ON position, there is a high pitch noise coming from the PCM. The trouble codes that come up are two things, short in the A/C relay and short in the Fan relay. But I just cant seem to figure out where the short is, does anyone have a diagram or know what all is connected to those relays? The only way to really get rid of that high pitch noise is by pulling the fuse for the PCM. Is it possible that just my PCM for some reason shorted?

 

I'll guess the high pitched squeal is the voltage regulators in the PCM tossing their lunch.
I've heard it before when the filter caps go bad, the regulators start singing.

 

So your suggesting a new PCM?