My 92 cummins charging system is not working. The altenator tested ok on the bench test at parts store. Put it back on, cleaned all connections and still nothing. Battery charged up ok on my battery charger. Parts store checked altenator on truck and it showed not working. Are itermittent alt. problems common? Any suggestions on fix would really be appreciated.

 

I not sure if your '92 has a PCM (power control module)on it, But mine had the same problem everything check fine but didn't charge. What it ended up being was the voltage regulator wire at PCM had come loose at the connector. I just recrimped it and problem was fixed. Yours may not be at the connector but you be able to ohm out the wire.

 

The PCM (next to the battery) has the voltage regulator built into it, and controls the field current to the alternator. Power for the alternator field is provided through the ASD relay (left fender) by the dark green/orange stripe wire(blue/black stripe at alternator), and the field is grounded by the PCM (pin 20... dark green wire). It is fairly common for the voltage regulator to fail within the PCM, thus requiring replacement of the PCM. I have wired an external (old style mopar) regulator into mine bypassing the pcm... if this is done, it causes the check engine light to stay on permanently unless you remove the bulb. Hope this helps.

 

I don't know if this applies to a 92 but what about that crank sensor? I've read on this forum that the crank sensor lets the computer know the engine is running and then allows the the alternator and the air conditioning to work. Does your A/C work?

 

It's most likely a crank sensor problem, like Tim said, if the A/C and cruise are dead that's your problem. It's usually just a broken wire in the harness going down to the sensor. Another possibility is a bad ASD relay, or a bad connection there. There's a row of 3 relays on the driver's side fender, front is ASD, center is starter, rear is A/C. Try swapping the A/C and ASD relays after you check out the crank sensor.

 

I wanna thank kerryneb,handymantim and wannadiesel for your replys. They all helped. My ac and cc still work so that eliminates the crank sensor. (By the way, where is that located?). I still need to trace the wiring down and check for bad connections from the pcm. (hey I am on vacation and been fishing all day...first things first) I really like the idea of bypassing the pcm with an old style regulator. I bought one today and think I have figured out how to wire it. I bought a transistorized regulator with two pins. According to the schematic that came with it, I will run one wire that goes through ignition switch to ign. pin on regulator and also to field terminal on alternator. The other wire goes from other alternator field term. to field term on regulator. What confuses me is I thought one of the alternator field terms would go to ground. I don't have to go fishing until tomorrow afternoon so yall got plenty of time to help!! Again, Thanks a million. This is a great site.

 

The regulator IS the ground. Before you give up on the PCM, swap the A/C and ASD relays like I suggested above. My truck had a little corrosion on the terminals in the ASD relay plug, a little scraping and some contact grease and the alt. was back up and charging.