Cpower666

I have a 1992 cummins w250 new battery,new battery cables, new alternator, new starter. I have checked all grounds and fusible links. All the lights and gauges work. I will drive it for twenty minutes shut it off then it won't restart unless I charge the battery. Brand new battery reads 12.4v when I recharge it. When I fire it up it reads 11.8v. The more it runs the more the voltage goes down until it won't restart. The truck is stock except for 4" straights and intake. Any suggestions would be appreciated. Thanks in advance.

oliver foster

When the PCM fails, the alternator stops sending charge to the battery.
I believe the wait to start light relays, cruise and such also stops working with a bad PCM.
I have heard of people using in line voltage regulator like the '89-'90 [and maybe '91.0?] trucks have.

j_martin

Obviously the alternator isn't putting out any current. Assuming it's good, there must be something wrong with the other wiring.

On the back of the alternator, the main heavy wire should have battery voltage on it at all times. If it doesn't, the fusible link between that terminal and the battery is bad.

The two lighter wires are the field supply. When the engine is running, one should have battery voltage supplied by the ASD relay. (blue wire) The other should be somewhere between battery voltage and ground. It is grounded by the voltage regulator in the PCM, or an external voltage regulator, depending on your setup and past modifications. (green wire)

If both appear to be at battery voltage, you can temporarily ground the green terminal and the alternator should charge, indicated by a slowing of the engine and an increase in battery voltage or light brightness. (under hood trouble light, for instance.)

There's several fusible links, relays, and connectors involved. Any one can be the problem.

If it appears the PCM is failed, there's several hot wires and (at least on my 93) a TPS signal that needs to be present before the PCM will operate anything.

Here's the diagram page from a 1993 manual, should be close.

Cpower666

I bought an external VR since my factory one is located inside the PCM. I plan on installing it tomorrow. Could it be that? Possibly the CPS? Or is it strictly a wiring issue? Are there fusible links between the alt and battery? I appreciate the quick responses. I would appreciate anything you guys have to throw at me. Really wanna get the rig back on the road.

93/4X4/CREWCAB

Keep in mind that if the PCM is bad and you put a external regulator to fix the charging problem that might fix that but the PCM also controls other things like the grid heater, speedo and the tranny if you have a auto. I had the same problem with my 93 and I bought a reman PCM from my local Dodge dealer for under $200 and it solved all my problems and I didnt have to alter anything.

j_martin

You totally missed the point of my post.

If yer rich, throw parts at it till it works. (begs the question, why are you driving a first gen.)

Using the diagrams, diagnose the problem to determine the bad part or connection, and repair that one thing.

Just a for instance, if the ASD relay is bad, the new voltage regulator you intend to install won't work. ASD relay is about a ten dollar part, and it can be diagnosed in a heartbeat by swapping it with the AC relay right beside it.

If you don't understand diagrams and meters, find somebody that does.

crazzywolfie

that is not 100% true. your speedo will work without the computer. the wire to the T's under the hood somewhere. one goes to the speedo and the other goes to the computer to control things like transmission. i know this because i was was bored and installed the speedo from my 91 in my 81 just to see if i could get it to work and it did but i hate how the electric speedo starts at 20km/h so i went back to the mechanical speedo.

Dean Snow

a lot of times the whole computer doesnt go bad. so far i have had just the voltage regulation part of the computer burn out on me twice on two different computers.

here is the easy and simple fix.

http://www.motorcityreman.com/chcovore1.html