I have what appears to be an electrical problem in my charging system. It seems to be with the voltage regulator. It's been going on for about a year now and has gotten worse in the last couple of weeks.

When the engine is started up, the voltage is usually low (<14v) for the first few minutes. Voltage will fluctuate as the plates cycle. Then, after several minutes or restarting, the voltage will usually increases to the needed 14.5v to 15.5v range and usually stays there, untill recently. Sometimes it will stay low long enough for the GEN light to come on. Now it has begun to slowly drop back down to about 12v to 13v and won't come back up.

It seems to be connected to cool weather: parked outside overnight, temps dropping as winter aproaches and now at it's worst with sub zero temps. The connection to temps may be coincidental. I'm not sure.

The Chilton Manual shows a v-reg that is mounted on the rear firewall. I ain't got one. The v-reg, I do have the firewall. I've been told by a local auto parts store that it is in the alternator. I don't think so. Everything I see here says that the v-reg is part of the PCM. My assumption is that that is the correct answer.

My questions:

1. Where is the v-reg on a '96 DCTD?

2. If it is in the PCM, are the PCMs interchangeable or are they highly individualized to match every minor modification to the engine control system as they are on many gasers, where they can have many different onboard computer configurations for any particular model and year?

3. If so, how do I identify which one I need to to be able to replace mine if it's bad?

4. Is there anywhere on line that has information about DCTD PCMs?

I'd like to become as informed about this aspect of my Dodge as I can for this problem and any future needs.

TIA for any help on this.
FF

 

Have your batteries been load tested yet?
Huge voltage drops, and slow recovery after the grid heaters engage is one sign of weak batteries.
Batteries lose capacity exponentialy as the temps drop.

 

This may be the same problem that I had a couple of days ago.

I fired up and drove about 10 minutes with my car trailer in two. I had to stop for coffee. ;D

The I restarted and drove about five minutes more and noticed the gen light on. So I pulled over and lifted the hood to make sure I didn't lose a belt and noticed a hot electrical smell. So I touch the alternator and it was very hot.

I turned around and went home.

Later I started it and it was charging fine.

Mine is also a 96. It also is outdoors and was probably around 40 deg overnight.

Could we be experiencing the same problem?

 

A few months ago I had a similar problem, generator light on and voltage jumping up and down. It turned out to be the grid heater relay mounted on the inner fender Under the battery drivers side. Just an idea.

 

Some alternators do have the voltage regualtor built in. Some have it external. Follow the wires off your alternator, if it goes to the batt then yours is internal. If it goes to an external volt regulator then you just found it.

 

ShovelHead:
I have not had a load test done this year. I did have one done last year when the problem first showed itself. They were O.K. then.
I pulled the batteries, cleaned them up and put them on a charger overnight a couple of days ago. One of the batteries was a bit slower to take on it's charge. That hints to me that it may be getting weaker.
But, the problem isn't batteries. The problem is low voltage in the electrical system that appears to be anything from from low to no output from the alternator. The way it is intermittent and usually gradual in nature, working fine for a while then crashing slowly or quickly, leaves me certain that it is not alternator failure.

Sonora Bob:
I have not checked the alternator for heat buildup when the problem is going on. But, I don't think that is happening. I've not noticed any hot odors from up front. I will take it out today to do some running around town and check it.
Mine is normally garaged when I intend to use it the next day. Especially in the winter. That's why I have noticed that the problem is more prevelent when it is parked outside overnight, or after operating it in cold weather.

wazzup:
This problem is distinctly different and seperate from the grid heaters cycling. Sometimes it begins after I'm on the road and at speed. Although, it is almost always slow to begin charging when first started up.

jrs_dodge_diesel:
I'd have to tearup the wire bundle to trace it down. No gonna go that far yet. But, I just looked at the schematic diagrams in the Chilton and Haynes manuals. They both show wiring from the alternator connecting to the PCM. Terminal B10 is the Gen Field Driver per the schematic. I think that is a v-reg function. Anyone disagree?

Thx for your input guys. I'm still looking for anything that'll give me more info about the PCM. I'm almost certain that it's the source of the trouble. But then, who knows...? Electrical problem make want to tear my hair out. Can't do that. It's falling out fast enough on it's own.

 

Easy with the hair. On start up my truck takes about 10 seconds to show any output from alternator. The problem with the grid heaters drove me nuts too. Sitting in front of the shop every thing was okay, normal output from alt. no swings on ammeter so on, get in and drive down the road and it would go crazy. Every bump I hit would cause the ammeter to show discharge like a bad alternator. I unhooked the heaters at the intake problem went away, ordered a new relay for seventy bucks. No problem since then, a local drive em in push em out place wanted to cut the wires and install a external regulator said it would work ok but the check eng light would stay on. That was not an option.

 

whazzup - I had a bouncing needle problem on my F-150. When I hit any bump the guage would swing down and act crazy. Seemed my battery connections were loose and dirty. Just another thing to check.

 

I have a question. Freeloader did you check the ground(s)? a funky ground can cause all sorts of problems. If it was light out I would go and look at mine and tell you where to check.
Tom

 

This is a bit of a longshot, but have you checked the belt tension? A slipping alternator belt can cause low voltage output.

 

The alternators are dumb units with no regulator. The regulator function is in the computer. To me it sounds like weak batteries. Possibly a cell shorting, look for boiling over while charging.

 

Been busy guys. Just came from the Dodge dealer. Spent some time looking at the shop service manual. I'm gonna get one. It's a good manual for my purposes. Much better and informative than both Haynes and Chilton together.

Called the local wrecking yards and several places on the West Coast today checking for availability of a used brain. NONE, NADA, ZIP, ZERO!!! If I could have found one it would have been about $200. I find that to be a bit ominous. There should be some around. Makes me think they may go bad very often.

I've found an East Coast dealer that sell Dodge parts on-line who wants $300 for a new one (They say it lists for over $425). Plus, they say that have Service manuals for $100. According to them it lists for $300. I'll check with Dyment just to see how honest they are.

Now, to make sure that it IS partially brain dead and needs a transplant.

MnTom:
from one of the manuals I looked at today, grounds in the charging system certainly could be the problem. Gonna start checking them out, maybe tomorrow. I hate having to trace electrical problems!!!

MexStan:
Don't think so, but I'll check it tomorrow too.

Haulin in Dixie:
Gonna check them tomorrow also. The battery shop where they came from (a local independent battery mfgr. held in the highest esteem by all for cold weather reliability.) will check them for me. Might even get them to check out the entire charging system too, actually diagnose the problem. That might be the easiest way to locate the problem. Depends on cost. I'm a notorious tightwad.

 

Not to suggest what anyone else should do, but if mine ever goes out I will add an electronic regulator from the earlier mopar systems. I am not real excited about all the basic systems being tied to the computer. If you really want to set up a nice system, use a regulator from an earlier big truck and you will have adjustable output.

 

[quote author=Haulin in Dixie link=board=5;threadid=22663;start=0#msg214394 date=1069858426]
Not to suggest what anyone else should do, but if mine ever goes out I will add an electronic regulator from the earlier mopar systems. I am not real excited about all the basic systems being tied to the computer. If you really want to set up a nice system, use a regulator from an earlier big truck and you will have adjustable output.
[/quote]

You have my attention. The last time I messed with a v-reg was ~25 years ago on a '37 Dodge ton & 1/2 I had at the time.
How about the electronic v-reg shown mounted on the rear firewall in the Chilton manual? I assume it refers to an earlier year model.
Would there be a better way to go?
Are there any potential conflicts with the brain-box and it's proper functioning?

If I can decide what v-reg to use, then I'll probably need advice to help figure out how to wire it in.

Notes:
I called Dyment a few minutes ago. They want $90 + $11.25 shipping for the service manual. Where'd that online dealer get their $300 regular price for it? I think someone's trying to pack my shorts with snow.

Also called the local dealer. They want ~$430 for the computer.

Thx

 

I don't know about the older trucks but my shop manuals says there's also a battery temperature sensor under the drivers side battery and the computer adjusts alternator output based on the battery tempuerature (if the battery gets too hot it lowers the output)