Fix it.

 

Well I went out and cleaned up a few body grounds and now its 17 ish volts steady

 

Still overcharging. Still chasing grounds

 

I don't see you saying anything about pin 20 at the PCM, that is the field driver, which actually is a variable ground to pull in the charge.

When you say still overcharging, is it steady now, or still on/off?

 

It was steady. Now its on off again. Pin 20 7.96 volts at idle.

 

New results. Key off ohms
pins 5- 2.0
11- 0.8
12- 0.8
20- 12.8
51- 60.0
Engine at idle volts
pin 5- 15.2
11- 18.2
12- 18.2
20- 07.6
51- 08.7

Im sure yall cen tell but I have no idea how this pcm works or what normal readings should be. Im very thankful for all the help. Its 28 degrees and spitting sleet and rain and ive been under the hood in my driveway most of the. Im trying like hell to figure it out guys. Hopefully y'all wont give up on me lol

 

Heres something new and odd. I just sat in my driveway for about 20 minutes idling with volts holding steady at 14ish and decided to go for a test drive. Reversed out of my driveway and before I could even shift into 2nd it pegged out again. Im obviously not as smart as yall at this but im just lost. Ive been chasing wires and redoing grounds for hours with no positive results.

 

Now ive noticed my brand new optima yellow top hissing out of the vents. Have I toasted it. I dont see how if its a ground it just came out of the blue. Ive put an alternator a cps and battery on all within the last 6 months or so. Could one of these have failed. I cant think of any other mods or additions ive done recently that would have brought this on though. Im just lost guys. Am I looking in the wrong places. Could it go inside the cab. Could it be a potitive wire grounding out somewhere causing this instead of a ground.

 

Hopefully it hasn't hurt your yellowtop, but you don't want to keep doing it.

There really isn't anything else that can be wrong, it is a simple setup, and so long as you have proven the ASD relay is in ( it is ), then 12 volts goes to the Alternator on one small terminal and the other small terminal goes to the PCM pin 20 and the ground is regulated to get the desired voltage. The CPS has to be working or the ASD relay would not be engaged, so rule that one out. The Alternator could POSSIBLY have an internal fault that would take it to ground and overcharge but that is a flyer for sure. You are seeing variable voltage at pin 20 as you should.....

Just for giggles, you say it ran for 20 minutes int he driveway at idle with zero issues, but when moving, you didn't even get to second before it pegged, could it be the engine moving and pulling a wire? Was the green wire going to pin 20 one of the ones you carefully searched for fray/crack? Also, sounds dumb, but you did carefully inspect the main batt. terminals for any signs of corrosion, specifically the negative ( not only the post area, but under the coating on the wire leading into the terminal )?

Here is a thread I started when I was having a no charge issue with one of mine. It isn't the same issue as yours, but they explained the operation of the system to me very well.

Perhaps something there will jog your brain?

https://www.dieseltruckresource.com/...estion-317538/

 

One other thing, do you have a local pull-a-part or friendly junkyard? The same Alternator was used for several years around that time, gassers, Jeep Grand Cherokees, etc ( As a matter of fact, I think the mini-vans are also the same )

Anyway, if you can get one cheap, all you have to do is swap the 7 rib pulley for your 8 rib. That would eliminate any possibility of it being the Alt.

Also, where are you located? If it is 28, you are probably down South.......

 

Yes I am located just outside of Temple Texas. I put a brand new negative battery cable on it several months ago. I chacked. Its good. I put new battery terminals on both cables when I did this as well. Both are still good. The green wire (pin 20) is the main reason I stripped my harness to trace it. Its good. Ive checked and checked and checked again and no loose connections or stripped wires. Thats why its baffling me. It should have been one of these things right. If not then by process of elimination it should either be the alternator or the pcm right?

 

The alternator, the pcm, or the wire between them.

Here's a thought. The field terminal when the alternator was tested was loose. Now it's tight. Disconnect the field wires on the alternator, (or all of them if it's one big slug) and tighten the field nuts down tight. Then measure the ohms between the field terminals and ground. Put some wiggle pressure on em when you're measuring.

Like others have said, don't run any battery, especially a sealed one, at 120 amps unregulated ( which is what is happening) for very long.

 

We can rule out the wires from alt to pcm. I have very very thoroughly checked and verified they are sound. Battery to body 0.0 ohms. Battery to block 0.0 ohms. Block to chassis 0.0 ohms. Chassis to body 0.0 ohms. Alternator to body 0.0 ohms. Alternator to block 0.0 ohms. The two small field terminals on alternator with key off 7.8 ohms. Truck at idle two small field terminals one read 17.8 volts and the other read 8.6 volts. Has to be pcm right?

 

As I said above, isolate those two terminals, put the nuts on them as if they were connected (torqued), and check the resistance to ground. If they are not completely isolated from ground, it will cause what you're seeing. "blank" Auto's generator test won't find that fault. It just checks for full field output and noise.

The problem is intermittent. Intermittent faults are tricky because you have to find and document the fault, which isn't always co-operative. I'm trying to help you do just that. When I ask you to do a test, it's because that test will determine a path that the diagnosis needs to follow.

The field drive from the PCM looks normal. You didn't document whether it was overcharging or normal at the time you took the reading. Of course that is critical information. A field short to ground mid coil could full field (nearly) the alternator and provide a negative voltage at the field terminal. Polarity of that reading is critical to the diagnosis, as is the current state (OC or normal) of affairs.

Sometimes intermittent problems can be flushed out with stress. Pulling and bending on a harness is an example of that. Sudden cold shock also sometimes works on electronic or electromechanical devices. An inverted can of office duster is a good source of sudden cold. A hair dryer could supply a little heat. If the problem normally shows up only after the engine warms up, it could need a little heat to manifest.

The field drive from the PCM is most likely the collector circuit of a bipolar transistor. Normal failure of that device is either wide open (won't charge) or shorted collector to emitter. (full charge, no relief) I know of only one family of transistors that can heal from a collector to emitter short, and that is a microsecond thing. Drove us nuts trying to figure out a major failure in a ferrite core memory back in the 1970's. The odds that that type of device (mesa bipolar) is in the PCM is zilch to unbelievable.

Of course the regulator circuit in the PCM could be failing due to a failing solder joint. I haven't heard of that happening, at least not often. Heat/cold shock testing should flush that out in the open. If a good salvage PCM were readily available, as it would be for a gasser, it would be worth substituting one in for testing. That would be a last resort here because of the expense, and the liklihood that a "rebuilt" could be worse than what you have.

hope it helps

 

Yes sorry Mr. Martin. These were done while overcharging. Did like you said. Took wires off two small field terminals. Put nuts back on and tightened them back daow. Key off top terminal read 2.9 ohms and 2.8 ohms on bottom terminal