I was driving home from work last night and ended up walking 7 miles home in the rain on a mountain road after my 2500 quit. The 2500 has a 5.9L gasoline engine with an automatic transmission.

As I was driving and had the heater, headlights and wipers going, I noticed the dash lights going dim, the headlights going dim and the wipers slowing down. The battery gauge was just above 8 volts. Knowing that this was likely signaling an alternator failure, I put the truck in neutral and tried to keep the RPMs up while going down hills. After a few moments, the tach started jumping and the truck quit running. I pulled over to the side of the road. All lights were working but still dim. The battery gauge still read 8V. I tried to start the engine, but it just clicked as if it wasn't getting enough power to turn the starter. I checked the battery connection and the belt. Both looked like they should. I then walked home.

Today, I returned to the truck to give it a look before going to an auto parts store. For kicks, I tried to start the truck, and it started. I wanted to see if the battery would charge, so I reved the engine a little. While holding my foot stationary on the gas, the RPMs would begin to drop. Turning on any lights would decrease power. I decided that if I could get it 2 miles down the road, I could park it at a friend's gas station, which was better than being on a tight mountain road. Just before arriving at the gas station, the electrical completely shut down regardless of having my foot on the gas and I was able to coast into the gas station. The battery gauge showed no voltage at that point.

To me, this sounds like an alternator problem EXCEPT the fact that keeping my foot on the gas didn't keep the system running, which I have been able to do with previous vehicles.

I just purchased this truck and absolutely LOVE it. I'd like to keep it running. The engine runs incredibly smooth and strong despite its age and the body is also in great shape.

Thank you for reading this post by a new member.

Adam

 

The way to test the charging system is with a voltmeter. Should be somewhere above 13V when the engine is running and drop back down to batte3ry voltage when the engine isn't running. By the sounds of things though you might have killed the battery by running it that low. A starting battery is probably going to start getting pissed whenever you try and discharge below about 12.5V or there abouts. They just aren't designed for that like a deep cycle battery which can go deeper discharged say to 12 or so Volts before you start being overly abusive.

 

could be the alternator or it might possibly be the voltage regulator gone bad. it would not be the first time i have read or heard of the VR in the computer go bad. maybe you can find a place to get the alternator tested.

 

I'll check the charging system with a DMM before I go to the parts store tomorrow.

CrazyWolfie, are you refering to a VR that is located on the ECC's circuit board (such as an LM---) or is it its own circuit?

 

Unfortunately, the voltage regulator is integrated into the PCM. That was a bad idea....... may have to pull the alt, and take it to have it tested.

 

ya i am referring to the vr that is located on the ECC's circuit board or whatever you want to call it. i have read people using an old style VR if the one in the ecc boards died. it is a lot cheaper than replacing the computer.

 

I build amplifiers from scratch for work and as a hobby. If the VR is physically accessible and can be replaced using a soldering iron and patience, I can do it. Of course, this may not even be necessary if the alternator turns out to be the problem.

The difficulty is that the closest place to buy auto parts is 30 miles from me, so I have to be certain of what I need before I take a trip to get it.

Adam

 

Need to test the alt, and see if it is bad... if it is, there's the problem, if it isn't, then, VR is toast. (most likely) Accessible though? Very good question. Don't know if anyone has dug that deep into the PCM.... and I haven't found any schematics for it anywhere.

 

Since my 2500 is 7 miles away and my other vehicle is on loan, I have to bum rides to get to it - kind of a hassle. I was just trying to stir a little educated conjecture in the meantime.
Are there typical symptoms for VR failure that differ from the symptoms of an alternator failure? The symptoms that I observed looked like alternator failure aside from being able to start the vehicle again the next day before it completely died 2 miles down the road, at which point it looked identical to an alternater failure. I just thought that the battery would hav been drained the prior day.

Adam

 

The battery will recover some when it sits for awhile... not much though mind.

It's impossible to tell which failed without testing though. Either way gives the exact same symptoms. Alternator stops charging, and engine quits running when voltage gets to low.... If the alternator tests good, VR is the culprit.