I have a 1998(.5) Dodge Ram 2500 24V Second Gen Cummins. TLDR: Truck not charging. Put new Nations 180 A alternator on it. Batteries are good. New ASD relay. Only measuring 12.2V at batteries while running. Also measuring 12.2V at B+ post of alternator. Checked all the grounds. Belt tightness, and basic stuff. Just found out not measuring any power at field leads off back of alternator. The tach did go out for a bit twice before it stopped charging and the cruise hasn't worked at all. I think these might indicate PCM. Also, the seat belt hack the PO had used (not sure all the details, but he did tell me about it) to get seat belts unlocked stopped working with the new alternator in and the seat belts are just locked now. Trying to figure out if problem is in ASD system, crank position sensor or PCM. Anyone got any ideas on how to determine this? Any help is greatly appreciated!


Details: Truck was new to me as of July. Ran fine until a month ago. Charging dropped to nothing and left me stranded. Took out batteries and alternator and had bench tested. All tested fine, but found out the alternator was not OEM and was undersized. Put everything back in the truck and it was running fine for about 2 weeks (I don't drive it much). Then it started only charging at 11.8V. So, I got a Nations 180A alternator as I'm planning on putting some accessories on the truck. I installed the new alternator and it still only shows 12.2V at the battery and the B+ post on alternator. A few weird things happened at the same time the old alternator stopped working right, The tach did go out for a bit twice which it hadn't done before and the cruise hasn't worked at all since I've had it. I think these might indicate PCM problem. Also, the seat belt hack the PO had used (not sure all the details, but he did tell me about it) to fix the seat belts being locked up stopped working with the new alternator in and the seat belts are just locked now. Previously they were locked up until you turned the key to on.
I replaced the ASD relay. I think there's a way to ground out the ASD relay box (don't know what you call the part the relay plugs in to) to diagnose, but I don't know which part of the relay box to ground. I've checked all the grounds, belt tightness and all the basic stuff. I think this all means it's in ASD system, crank position sensor or PCM. Anyone got any ideas on how to diagnose this? Any help is greatly appreciated!

 

did you get this problem resolved? A long time ago I was having all kinds of odd problems not charging or way over charging. Tach went hay wire for a better term . I asked on the forums and i got a few suggestions. I think i bought a service manual , and went down the check list and finally i bought a rebuilt pcm from Mopar. A online discount dealer . That fixed all my problems except one .. The cruise would drop off when I hit a small dip in the road. I installed a spring to the brake peddle. That fixed that problem. This has to be 10 or 15 years ago . Yea I checked even the pins on the pcm for corrosion, bad ground ect ect . ..later on I noticed other folks were having the same problem. Back then most said no its not the pcm . Mine was ..this is not to say your is . Seems like the service manual suggested the pcm after all of the checks. Do you know anyone you could borrow a pcm off there truck just to try

 

So, I did get it charging by adding an external voltage regulator to go around the PCM. It's charging, but only at 13.5 V, which seems to be the VR setting. I found an issue in the battery temp sensor so I replaced that as well. From what I can tell there is an intermittent problem in the PCM. I got a lot of good advice from the people at Diesel ECM Exchange and considered sending them the PCM to diagnose and repair if needed, but don't have the funds right now. So, it's running for now and I need to send in the PCM or try to rebuild it myself at some point.

 

The pcm is the root of many electrical issues with these rigs. I think you are on the right track...

Kurt