I have a 1994 Dodge ram 1500 four-wheel drive with the 5.2 it is not charging the battery in it the battery was in good condition but this truck has completely drained the battery I have to recharge it and about 20 minutes after I charge it if I start it up it'll run for about 20 minutes or so and it dies again I can't figure out what the problem is

 

Alternator first guess.

 

Yeah are you seeing 13.8 to 14.4V at battery while running? I'm guessing not

 

I'd suggest removing the alternator and have it checked for voltage output within specs. Most auto parts stores will check them for free. On the 2nd gen trucks, the PCM regulates the alternator voltage, assuming the alternator is producing voltage within an acceptable range.

 

Even in '94? For some reason i thought the PCM regulation started a couple years later?

 

That was already a thing in '94. However getting the alternator checked in a parts store seems to be more miss than hit.

OP: Check resistance between alternator output and battery positive. With engine running, check dark blue wire at alternator for 12V, and then measure voltage on the dark green wire. It should be lower if the PCM is grounding that side to control the alternator output.

 

Dennisjoyner88, I'm in the same boat with my 98 1500 5.2L. Battery died on 4/05. Replaced it at NAPA. 3 weeks later, it wasn't charging, so NAPA replaced it under warranty because it had a bad cell. I replaced the Positive post connector at the same time.

On May 5th, the gauge light came on, and I could see that my battery wasn't charging. Limped into another NAPA 20 miles away and used up the battery the way. The counterman - a very nice and knowledgable guy named Dave - immediately said that it sounded like my alternator was shot. I asked if they had one in stock, but of course they didn't. Dave said he would install it for me if they did have one, but said he'd put my battery on their fast charger until closing so I could make it home, which was 25 miles away from the store. While waiting, I called the NAPA near my home, and ordered the one Dave had shown me on the store computer. Made it home, with the truck dying right in front of my driveway.

I picked up the new alternator the next day, and had them check the core that I brought in. The charging circuit was dead, so went home and installed the new one. It was a 2-man job, because the outside diameter of the pulley was larger that the Denso it replaced, and I had to lever the belt onto the power steering pulley with a screwdriver while my son held off the tensioning pulley.

3 days later, I had to drive 23 miles to pick up some of the materials for a bath remodel job, and 20 miles in the check gauges light chimed at me, and I could see that, once again, the battery wasn't charging. I picked up the materials, and knew that I could make it back to the NAPA store where Dave worked, barely. Dave wasn't working, but the Manager, Todd, was and I asked him if they could once again charge my battery for me so I could get home. Very kindly, they agreed, and while talking with Todd, I asked him if the Voltage regulator was on the back side of the Alternator. He told me no, that it was part of the ECM (PCM), but he had seen some videos about putting an external voltage regulator in to bypass the ECM. He was pretty sure that the ECM was the culprit. When I ran my OBD, I saw that I had thrown a P1682 code about a month ago. One of the possible explanations was the PCM, and since I had had no ignition problems, I think I have isolated my issue.

After watching a couple of videos, I decided against the external voltage regulator, and I'm just going to buy a remanufactured PCM. It's more expensive, but it's plug-n-play, without the wiring issues, and my time is worth more than what I'd save.

I am interested in any responses, and of course, hope this story helps the next guy!

 

There is a fuse in the pdc, It goes between the alternator and the rest of the system. So if it blows you get no power. Most forget to check it and assume it's alternator. And adding a external regulator is not a big deal.

 

Thanks, Man! I checked the fuse block and Relays, etc, when the battery died the first time. Discovered some moron replaced the 50amp fuse with a 40. It wasn't blown, but replaced it anyway. Yes, the External VR is simple enough, but I don't want to spend my time doing it, nor deal with the extra wiring in the engine compartment. Thanks for the response.