I have a 92' and the original PCM blew the charge cicuit a year ago and I temporarily fixed with an external regulator until I replaced the PCM. I replaced the PCM and around 4K miles later it blew again so I put the external regulator back on and it worked ok for about 2K miles and the regulator fried causing the alt to over charge the battery. I got home and replaced the battery and regulator and it wouldn't charge. I fielded the alt to see if it was the problem and it charges. Took it to 3 different places and it tests fine. Replaced the PCM under warranty and nothing. I have good continuity across all wires for the charging system. I added multiple new 4GA grounds to the engine and still nothing with the PCM, external regulator or the transpo internal regulator. Does anybody have any ideas?

Thanks,
Simon

 

You say you have good continuity, but have you tried testing for voltage drops.

All it takes is one strand inside the wire to have good continuity. With doing live voltage testing you can see how good or bad the wires are.

To test this way you have the vehicle together and running. You start by knowing what battery voltage is. Then you start doing voltage tests on each wire that is involved in the problem. You never unhook any wire when you are testing, so you have a true "loaded" circuit. If any of the circuits are in question you will have a lower voltage past the problem area. This is with using a common ground.

The second way to do the testing is to run your voltage meter in parallel with each wire you are testing. You would test the wire with the ground lead of the tester at, in your case the PCM and the positive lead of the meter at your alternator on the same wire in the circuit. If the is any problem with any part of the wire the voltage on the meter with read >0.5 Volts. Again with this way of testing the vehicle is intact.

HTH
Glenn

 

Checked all of the wires for voltage drops and found the charge wire dropping to 6.5v after it passed through the connector at the fenderwell to the alt harness. I replaced the entire harness from the battery to the alt andstill notheing. The entire factory charging sytem has been by-passed (PCM and all factory wiring)with new wires to an external regulator and even tried an internal regulator from transpo. I have added 3 new grounds (battery cables) 1 from the block to the frame, 1 from the engine to the firewall and 1 from the block to the core support. All the grounds are good, clean and overkill. The alt still does not charge!

I am now completely baffeled and extremely frustrated.

 

The alternator has two field connections.
If you are getting 12 volts (9.5 volts) from both and you are grounded you will get charge. Be sure your ignition side field is getting current then tickle the other side momentarily and look for out put. Conversely hot up the regulator side and tickle the ignition side and look for output. If none you have a bad alternator. Look at how a shop tests them off the rig.

 

I can field the alt to charge and it has been tested 3 times by 3 different shops and all test it as being good. The 3rd shop even went as far as to open it up and give it a good once over and it all checks out good. With everything being stand alone and not hooked up through the factory wiring makes it even more baffeling.

 

Mine is in an old RV and works fine with a stand-alone Voltage regulator.
I don't have much factory wiring left. There aren't that many wires so maybe you can shunt around each them to see if you can isolate any shorts. If you find it you can fix it or stay with the shunt. Whatever you learn; share it.

 

mine drove me crazy had reg grounded to alt ect ,when i jumped the hot wire to the batt it worked,used another soruce for hot wire and no more troubles

 

you can play with that wireing forever expeshily on a dodge crysler product for some reason if it was me i would take alt in an have a self exciting self regulating single wire regulater installed an be done with the problem for good.

 

Check the crank sensor. If you have bypassed everything this should not be an issue, but since you are going crazy it's worth a try.

 

Bringing this back up.

Nothing has changed. I have taken the alt in and had it tested again and it charges like it is supposed to on the bench but won't do anything in the truck. I have bypassed all the factory charge wire pieces with one wire from the battery to the alt to get rid of the voltage drop I had at the alt/AC harness and nothing changed. It will not field no matter where I get the power from which post I ground or power up. Nor will it charge with an external regulator or an internal regulator.

 

mine drove me nuts and i hit the alt with a 1/2 drive rachet and it worked lol

 

Maybe you need to put the belt back on it? Just kidding-----hope you figger it out.

 

I know this might not pertain to you but who knows, maybe it will. I have one question to ask first! Does your ac still work? If not check your crank positioning sensor! My brother had the exact same issue one time on his 93 and we started troubleshooting and found that the ac didnt work either! It was fall so we got lucky! It turned out that the balancer had broken, causing it to not spin in a perfect circle. This in turn rubbed the crank sensor ruining it! It turns out that this sensor tells the computer that the motor is running. Without this signal 2 main things will not work (at all)! The ac and the charging system! I hope this helps you or someone else down the road out! Robert

 

There's a good chance you need an Altenator. Where did you get it tested? Napa, Autozone or some other $8.00/hours part swapping place. Did you go to an electrical repair shop?

Mine tested fine on the bench but wouldn't charge with PCM regulation or external regulation. I opened it up and saw the slip rings inside had a bit of wear but nothing else.

https://www.dieseltruckresource.com/...highlight=code

Just a thought.

 

I had it at a Alternator/starter repair shop. The guy has been doing it for 50 years or something like that so I trust him. I don't trust the mcparts store guys to tell me the sky is blue.

The factory wiring has been removed from the equation including the pcm and crank sensor and the A/C does work.

The only thing I can think of that makes any sense (and I might be grasping at straws here) is that something is grounding out and feeding back through the engine and making the alt think that it has a full charge so it doesn't see the need to charge.