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.

 

[pentode]

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.

Yes, I don’t know how they test alternators at Autozone but if it were me I’d really like to get a scope on the alternator output and see if it’s got a big AC component or something, which I believe you mentioned earlier. I’d also like to nail down whether the truck actually does die with 13.8V applied to the B+.

One of these things will surely lead to the problem.

 

[dean94]

What would be best way to test voltage to see if truck shuts off I've been using jumper cables from another running vehicle that was putting out 13.6 at running cars battery. And I don't have a way to check ac voltage from alternator other than a digital multimeter. I can see if the place that rebuilt alternator can check for ac voltage when they open back up

 

[pentode]

What would be best way to test voltage to see if truck shuts off I've been using jumper cables from another running vehicle that was putting out 13.6 at running cars battery. And I don't have a way to check ac voltage from alternator other than a digital multimeter. I can see if the place that rebuilt alternator can check for ac voltage when they open back up

I would say jumper cables from a working, running vehicle to your battery should clear that question up just fine. No need to worry about exact voltages right now, I’m just curious what the behavior is.

 

[dean94]

hooked jumper cables up to it while it was running it just died. While jumper cables was hooked up tried to restart it it just backfires every so often it may decide to fire up for a split second and just die same way with alternator hooked up mainly backfire but once in blue moon it may fire up for split second and just die and back to backfiring

 

[pentode]

hooked jumper cables up to it while it was running it just died. While jumper cables was hooked up tried to restart it it just backfires every so often it may decide to fire up for a split second and just die same way with alternator hooked up mainly backfire but once in blue moon it may fire up for split second and just die and back to backfiring

Ok, that’s good info. I’m going be thinking about what the heck might be going on, as will the other guys I’m sure.

 

[Mechrick]

The black, barrel shaped items on the circuit board are the caps and they look ok.

Now I'm going to suggest check PCM outputs. Probably the easiest way is to unplug one injector at a time to see if it will run with the alternator connected. You can ohm them out as well, should be around 14 ohms each. Other items include the canister purge solenoid, the EGR solenoid, and if equipped, the air injection solenoids. Just unplug them one by one and see if it runs...

What could be happening is the PCM is saving itself by shutting down a circuit that is drawing excessive current.

 

[franklin2]

I need to get a summary of what we know. Tell me if this is exactly correct. Correct anything if it is wrong.

1. Everything hooked up, truck will not run.

2. Everything hooked up, the large alternator wire disconnected, the truck runs fine but does not charge of course.

3. With truck running normally, alternator large wire off, as soon as the large alternator wire is hooked up with the engine running the engine backfires and dies.

4. The latest test; Engine running, it's alternator large wire disconnected. While it's running you connect jumper cables from another vehicle to the trucks battery and it backfires and dies.

Is all the above correct?

 

[dean94]

Everything hooked up truck backfires or once in a blue fire up and immediately quit. Belt off alternator or main wire disconnected truck runs. If main wire is disconnected truck will fire up and run and soon as main wire is touched or connected to fender well solenoid it just quits. Belt off or main wire disconnected while truck is running connecting jumper cable makes truck quit and if tried to restart while jumper cables are hooked up truck will backfire or once in blue moon run then quit immediately

 

[franklin2]

What are you doing in both cases, hooking the truck alternator wire up or hooking another vehicle's battery up to the truck? In both cases, you are increasing the battery voltage. What does that mean? I do not know.

I think the 42 volt is a red herring, you got that because the alternator did not have a load on it.