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

[dean94]

Meter was on dc volts I'm using a cen tech voltmeter had it on 20 volt dc and it showed a 1 so moved it up to 200 volt dc and got the 42 volt dc could my computer be fried causing issues

 

[pentode]

Meter was on dc volts I'm using a cen tech voltmeter had it on 20 volt dc and it showed a 1 so moved it up to 200 volt dc and got the 42 volt dc could my computer be fried causing issues

It won’t be the computer, no.

I have a couple basic questions just to make sure I’m understanding this clearly. Have you tested the voltage across the battery with the truck running? I’m just wondering where you’re taking this measurement where you’re getting 42V.

I doubt it’s related but have you checked the fusible link C?

Am I not seeing something right or can we not fairly confidently condemn the regulator, and therefore the alternator? Someone sanity check me here.

EDIT: just thinking about this the last few minutes, if there's really 42V on the 12v rail in that truck, the computer, radio and a few other bits might be hanging on by a thread, but I would think everything that's not internally regulated, such as all the light bulbs, would (*should) be blown to bits by now.

 

[dean94]

Truck won't run with alternator hooked up but will run with it unhooked so I tested wire that runs from stud on back of alternator that runs to fender well solenoid unhooked from solenoid side. Is fuseable link c on the wire that runs on alternator wire that runs from stud to fender well solenoid. Alternator been checked twice good both times according to oriellys

 

[pentode]

Sorry, going back and reading through a second time I realize you've answered most of my questions already.

There's one thing sticking with me now. You may have done this already but just to confirm - if your truck is running and you attach jumper cables from your battery to a running vehicle (or a battery producing 13+ volts or maybe a battery charger) your truck dies? Am I getting that right?

 

[franklin2]

Sorry, going back and reading through a second time I realize you've answered most of my questions already.

There's one thing sticking with me now. You may have done this already but just to confirm - if your truck is running and you attach jumper cables from your battery to a running vehicle (or a battery producing 13+ volts or maybe a battery charger) your truck dies? Am I getting that right?

From what I am getting, he hooks his alternator up and the truck dies. Unhooked it runs, but of course does not charge.

He said he is getting battery voltage on the output stud of the alternator, everything off. That tells me the large output wire is good and connected to the battery. But that does not explain why he is getting 42 volts.

Though thinking about it now, the only way he is getting 42 volts is with the alternator disconnected, the truck will not run otherwise. So having the alternator wire hanging out there with nothing hooked to it might not be a good test, the 42v may be a red herring.

The alternator can produce near 100 volts if it's told to go wide open and the rpm is high enough. The only thing that holds the voltage down is the battery. Usually if there is a failure in the regulator and the alternator goes wide open connected to the battery, the battery may reach 18v or so, and sit there and start boiling, but it tries as good as it can to hold the voltage down to a reasonable level.

 

[pentode]

From what I am getting, he hooks his alternator up and the truck dies. Unhooked it runs, but of course does not charge.

He said he is getting battery voltage on the output stud of the alternator, everything off. That tells me the large output wire is good and connected to the battery. But that does not explain why he is getting 42 volts.

Though thinking about it now, the only way he is getting 42 volts is with the alternator disconnected, the truck will not run otherwise. So having the alternator wire hanging out there with nothing hooked to it might not be a good test, the 42v may be a red herring.

Yes, agreed, I think the disconnected alternator is causing the voltage regulator to freak out.

What fuse number and also with alternator unhooked and trying another car as battery charger while it runs it just dies so anything above battery power makes it die

It's the second part here that I'm trying to clarify in my head. If the truck runs fine on battery voltage but dies with charging voltage, that's definitely the major clue- I just have no idea what it means. . I have a couple theories but I want to make sure I'm understanding first.

 

[pentode]

What's the ignition system on a 94, it's distributor/coil right? It's not coil on plug is it?

Here's what we know: timing is good, compression is good, fuel delivery is good, computer must be alive and working to deliver fuel, no? So what could suffer from a 1-2V increase that would cause the engine not to run? It won't be the computer, that's internally regulated. Fuel pump? Really shouldn't be. Coil? That would be really very strange but is it possible?

How many sensors does that engine need to run and what are the odds any of them would be that sensitive to voltage?

 

[Mechrick]

So what could suffer from a 1-2V increase that would cause the engine not to run?

When I first read the symptom, I immediately thought of the GM V6's that the injectors shorted out. They would come in on the hook, and we would disconnect the alternator and sometimes that was enough to drop the current through the shorted injector to allow us to limp them in the shop, so yes, something shorted that's an output of the PCM could cause this. But injectors don't short out in Fords, it would have to be something else.

 

[dean94]

It's got the coil packs no distributor 8 spark plugs federal emission truck shouldnt have cam sensor

 

[Mechrick]

Just as an FYI, you should NEVER disconnect the battery or the B+ terminal to the alternator if an engine is running on any vehicle that has semiconductors (which is everything after 1976). You are asking for trouble if you do.

Just to clarify, was the 42v reading happening with the alternator connected, and if not, which wire(s) were disconnected?

 

[pentode]

When I first read the symptom, I immediately thought of the GM V6's that the injectors shorted out. They would come in on the hook, and we would disconnect the alternator and sometimes that was enough to drop the current through the shorted injector to allow us to limp them in the shop, so yes, something shorted that's an output of the PCM could cause this. But injectors don't short out in Fords, it would have to be something else.

This is why there's no substitute for a mechanic's experience. I've seen all different sorts of coil windings break down in lots of weird ways. I'm putting this one in the memory bank - every day is a good day to learn something, even Christmas.

 

[dean94]

Just main wire with car off and battery disconnected. Or I would take the main belt off to see if it would run.

 

[pentode]

It's got the coil packs no distributor 8 spark plugs federal emission truck shouldnt have cam sensor

Ah yes, the 2 plug head. Should have remembered that. I think you're about to close in on a diagnosis here.

 

[dean94]

I have also changed ignition control module when truck first died on me