Greg@RME

I'm clueless.... I was driving my truck ('99 CTD, 200k+ miles on the ticker) home from work today, notices the Voltage gauge hovering around 11-12v and figured my Alt. was shot.

I drove 40 minutes from my job site to my neighborhood & stopped at a Checker to have them double check the charging system. I left the truck running, went inside & grabbed the genious behing the desk. He hooks up his fancy little computer (with no Voltage reading, ) that tests the entire system and begins the test. As the truck is running, he's looking at the engine, he askes me if it's the V-10! Idiot!!!!

To complete the test, he has me shut it off and restart it. It won't start... We jump it & he tells me what I thought... the Alternator is dead. They don't have one in stock... I call around, find one 30 minuites away, at the dealer.... for $300!!!

So I change it at home, jump-start the truck and check the Volatge w/ my Voltmeter once it's running... 12.0 to 12.1. I left it running for about 30 minutes, hoping it would charge the Batterys and level out at 13.5-14 Volts. It never did, still charges at 12.1 Volts. I can shut the truck off, re-start it and get the same effect. If I put the Positive lead of the Volt Meter on the large wire coming off the back of the Alternator, it still reads 12v.

If I disconnect the terminals on the battery while it's running, it dies. I have been working on it all evening & I'm totally fustrated. Could it be that both batteries are dead & the new Alternator is charging just enough to keep it running? How can 2 batteries die at the same time, if so? Also, why wouldn't a brand new, Mopar Alt. be putting out more than 12v???

I'm going to miss work tomorrow with less than a month on the new job. Plus, I was supposed to head out of town for an event across the state... probably going to miss that, too.

So, if anyone has any helpful advice, fell free to offer it.... cause I'm in need...

j-fox

Put a charger on it for the night and try it tomorrow.
The computer regulates the rate of charge. But check everything first.
How old are the batteries?

Greg@RME

I don't have a charger here...

The computer regualtes the Voltage? ***?! So it the Alternator regulated externally? If so, could the Regualtor be bad?

Age of the Batteries? I have no idea... I bought the truck used about a year ago.

Thanks for the input!!

Haulin_in_Dixie

Yes, it is externally regulated by the PCM. I will give you the test to check the system. There is a plug on the back of the alternator that has two terminals. Unplug it and on the alternator, connect one termanal to ground and the the other to the battery plus while it is running. It should jump up to 15 or 16 volts at the batteries and moan from charging. With this done and if it charges right (too high), the PCM circuit is bad.

Dodge and most will tell you that you have to change the PCM ($$$) but you can add an external regulator to it. I have done several, works real good, only costs about $12 bucks.

To do this you get a regulator for a 1979 Dodge pickup truck, 318 engine. Many more do the same but this one is accurate for the use. The regulator has two terminals, the alternator has two terminals (the small ones). Hook the two alternator terminals to the two regulator terminals, does not matter which ones to which. Now on the regulator, it originally had three terminals, two on the bottom, one at the point at the top. Sort of like a pyramid. Looking at it like that with the wide at the bottom and the one at the top of the point, connect the top terminal to 12v key on source. The ASD relay output works well for this. All that is left is to hook a ground wire between the alternator and the regulator where it is bolted down. Self tapping screws work well.

If you mix the 12v feed terminal up the regulator will smoke and not work. Make sure of the terminal that gets the key on 12v.


..............O----------------------O----------------- +12v
......X...........O------------------O

..............reg..........................alt.

Don't look at the periods, the program does not accept spaces. The O's are terminals, The X is a blank space that was designed for a terminal, but does not have one. Mine did not charge right without the ground wire between the alternator and the regulator.

Just leave the disconnected original wires at the alternator taped off. It will set no codes or show any other non stock operation. This will save a few hundred dollars, especially since you already went for an alternator. Next time this happens, get an alternator for a 1998 Dakota, 136 amp, same alternator except that the pully is wrong and the terminals have nuts instead of the plug. Costs half as much. The pully interchanges with an impact wrench, is not a press on.

Shovelhead

You didn't recently change the oil filter did you?

If you hit the exposed stud on the back of the alternator with a metalic strap wrench, it will blow a fuse.

Might want to have the batteries tested also.
A battery that's taken "the big dirt nap" won't accept a charge.

Haulin_in_Dixie

He said that he had 12 volts at the large stud on the alternator, if so the fuse is ok.

On major word of caution on this and any other system with an alternator, do not under any circumstances, disconnect the batteries while it is running. That will take out all kinds of stuff. YOu might get away with it, but usually not.

Greg@RME

No, Oil Change was a couple months ago. Filter wrench handle is plastic covered anyhow.

I did just check the fuse, but it's fine.

As for the batteries, I'm going to have to test them since I don't know what else it is, but if the Alt is only putting out 12v, then I'd conclude that it's not a battery problem.

Greg@RME

I'm going to check the PCM next, I think that may be the problem. Do you happen to know what one costs? Is it a Dealer Only part?

Greg@RME

Great.... now you tell me.

That's how I used to check if a vehicle was running off the batterys... everything seems OK so far. I'll make sure I don't do it again!



Oh, and to everyone that's contributed... thanks a TON! It's nice to have knowlegable people within a few strokes of the keys. You guys rock!

Outrider

Old race trick your alt shaft will be magnitized when charging.Dont forget to bring your rpm's up above idel when checking it.Get a battery charger if you can.

greatwhite

First things first. If the output from the alternator is 12 - 12.1V, the alternator is faulty. 13.4 minimum or you are discharging. A 12v battery is really 13.2, but unlucky 13 and all . Please remember this... An Alternator Is Not A Battery Charger... and using it for this will kill it dead. It is a battery maintainer.
If one battery is bad it will take out the second battery in a remarkably short time. The problem is that you likely won't ntice one toasty battery until it takes out the second one and/or the alternator.
My advice is to get the new alternator tested where you bought it and it will probably be replaced. Get your batteries load tested and maybe you will get away with one or maybe not.

Haulin_in_Dixie

Not trying to be difficult, but this post is just confusing the issue. A 12 volt battery fully charged will read about 12.6 on a voltmeter. The regulator needs to be checked to see if it is functioning, in this case it is the PCM. While his batteries may be weak, they are showing 12.2 which is slightly below full charge. Even if these batteries are weak they would not hinder a proper operating charging system to achieve full voltage status while running.

While not charging fully dead batteries is very rough on an alternator, and can damage it, in essence the alternator is exactly that a battery charger. You run your batteries down on a back road and get it jump started. You tell me then that this is not a charging system. If mine would not handle that situation I would be making changes to get a system that does.

You have an alternator that is externally regulated. Either unit being bad can and will stop it from charging. The regulator can make it charge too high, too low, or not at all. This one is also externally excited and must have a battery with some juice to even get started.

He has replaced the alternator and now must be checked to see if the regulator is functioning, which in this case is the PCM. The batteries have enough juice to operate the system.

greatwhite

So sorry haulin'. Guess that the time I spent with the East-Penn battery rep. and the Accu-tec reman alt., start, and gen rep was a waste. As were the tech and trouble manuals I got. You can't load test a battery below 12.6v and at 12.4 I doubt it will start your engine. I stand by my voltage outputs. Rick

Greg@RME

Well, I tried testing the PCM by jumping it straight to the battery... no Voltage change. PCM is good!?!

I pulled the new Alt off and took it to Checker & Auto Zone to have them test it & make sure the *new* Mopar Alternator was good... They can't even test the Alt, since it's on a Diesel! I'm still totally lost. I think I'm going to take to the dealer & pay them to diagnose it. I hate to do that, but I don't know what else to do!

Haulin_in_Dixie