Need help on 94 ranger either short or bad alternator or something else

[franklin2]

So it runs with the belt off, but alternator connected?

At this point I'm going to suggest removing the PCM, taking the cover off and getting a good look at the electrolytic capacitors on the circuit board. Look for swelling or leaking of the barrel-shaped caps, if they leak there will be a white stain on the circuit board.

If this checks ok, then you will be unplugging and checking *all* of the PCM's outputs. First things first though.

If he has a PCM problem, why would it run ok on just the battery?

 

[SenorNoob]

The only way this makes sense is if the alternator is overcharging or has some AC on the output that is causing the PCM to shut itself off with some kind of protection circuit.

 

[dean94]

I don't really see anything wrong with ecm board

 

[pentode]

What's going on with that card edge connector in the second picture? Looks like it's covered in butterscotch fudge. Is that connector used in the truck or is that just for factory diagnostics or something?

I'm just looking for anything/everything abnormal.

 

[alwaysFlOoReD]

I believe that's a port used for diagnostics or a daughter board in earlier iterations.

 

[SenorNoob]

Isn't that the J3 port? Same one used for programmable tune memory modules?

Looks like very old dielectric grease.

But I fail to see how having the alternator disconnected makes anything work unless the alternator is outputting something it shouldn't be.