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Alternator / voltage regulator

130K views 36 replies 20 participants last post by  blackimpala 
#1 ·
Hi my 96 amp metor gauge is about at 12.5 volts until I get up to 55mph. What I would like to no is there a voltage regulator, or is it built into the alternator. thanks
 
#2 ·
The regulator is built into the PCM (computer) and costs $500 plus to replace.

Once you are certain the problem isn't the alternator or batteries you can disconnect the PCM regulator and use an external one. It's easy, cheap and won't effect anything else. Any 12 volt regulator will work. Remove and tape the small wires on the alt replace as in the picture below. Make certain the switched positive is at the top of triangular connector, the other two wires are interchangeable. The regulator doesn't have to be like the one below, in fact the number on it is no good.
 

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#4 · (Edited)
Start your truck, then disconnect both batteries, if all your lights and everything still work and the truck still runs, alternator is doing its job, if not, the alternator isn't doing anything or you have a bad connection..

Another way gauranteeing its the alternator is with a voltometer. Hook it to the batteries when its not running and it should be around 12V, when you start it up you should be up to around 14Volts. If not, then its the alternator, but I would run through all the wires and make sure they aren't corroded or anything and that everything is getting a connection...
 
#7 ·
Don't be so sure. The alternator is just the slave, without the PCM to make it charge it sits cold. Unhook the two small field wires located on the back of the alternator attached with 8mm nuts. Keep them away from grounding on the block etc. Attach two jumper wires, polarity doesn't matter...one to each stud, then the other ends to positive and the other to negative. This will full field the alternator and bypass the regulator. I wouldn't hook up the jumpers until the truck is running. It will display full output so don't leave it that way but for a couple of seconds. Voltage can go sky high by full fielding. Once you have done this, leave the truck running and using a voltmeter check for voltage acrosss the terminals you took off. One wire is pos and the other neg, you should see between 7-12 volts. This will tell you the PCM is supplying field voltage and current to the alternator. In which case keep looking. If the alternator didn't labor the engine, or show high voltage on a meter, it is most likely short on brushes. If it did, well keep looking again.

I wouldn't go throwing an alternator at it until you've diagnosed it down a little further. Taking off the batt cables is not a good thing to do to modern charging systems, and it still doesn't tell you the problem with the charging system.

GL
Chris
 
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#13 ·
Take the alternator off and take it to a shop that does alternator repairs and rebuilds (not a Autozone or NAPA, etc.). They will check it out using a scope and under load. If it's bad, have it rebuilt. If it's good, you may have a PCM or wiring problem (have you checked your grounds?); set up a external regulator for it.
 
#14 ·
I found the culprit, only I don't know quite what it is called. It is some sort of 3 pronged sensor that sits right at the front and center of the engine and goes to the crank or something. This had vibrated loose and just needed to be pushed back together. I just happened to see it had a bit of a gap from being totally closed.

Anyway thanks to all who help out clueless guys like me save some money and learn a little about the truck.:party018:
 
#15 ·
Sounds like you found a messed up engine speed sensor (ESS)
If it was the problem you should of had many more symptoms.
If the ESS doesn't pick up a tach signal it tells the PCM the engine isn't running, nothing electronic will work.
 
#16 ·
The ESS was only partly open (not separate) and the tach has been a joke for a long time. I'm guessing it has been slowly creeping apart with maybe some sort of connection, don't know if this makes sense but now tach works and batteries are getting charged. :confused013:

Once again, thanks to this forum now I have replaced my oil pressure sensor, fuel shutoff solenoid and hopefully solved my charging problem.:headbang:
 
#17 ·
I have a 1999 3500 Dodge Cummins Diesel with a Denso alternator. The instructions I have read for replacing the PCM with an external regulator all mention two posts on the back of the alternator. Mine doesn't have two posts but it does have a connector that connects the computer to the alternator. Can I just clip the wires on this plug and wire the external regulator to this plug? I have already mounted my Mopar regulator- I just need to wire it....

Rusty
 
#25 ·
Alt Rebuild kit

Gino's garage sells an alt rebuild kit, has new bearings and brushes, not diodes. I rebuilt mine and it works sweet. carefull getting the pulley off as it is cast and will crack if you pry it with a screw driver. if it does, make sure you file the rough edges:banghead:
 
#35 ·
14 volts is good



Yes, 14 to 14.5 is what it should run at, all those little electrons run down hill and fill the battery.:stirpot: A good PCM and Alternator will hold a steady 14 - 14.5 volts going down road with stereo, driving/fog lights, headlights, cooling fans ( yes, I built my own Dual Electric cooling fans setup for $120) and headlights on.:shock:

The whole purpose of voltage regulator is to respond to loads and vary output of Alternator to compensate.:party018:
 
#30 ·
The voltage regulator is in the computer.
To test the alternator on the vehicle you disconnect the wiring from the back of the alternator, all but the main battery wire. If you have the two posts for the wiring you ground one of the terminals then run full power to the other (connect to the main battery post on the alternator). Plugins are the same but more difficult. It does not matter which of the two terminals on the alternator you ground and which you run full power. This will by-pass the PCM alternator control and will make the alternator run full blast. Use your multi meter at the battery and on high idle (about 1000 rpm's) you need to build up to at least 15 volts. Do not run this to long or allow it to go over 16 volts at the battery. Over 16 volts and it can blow light bulbs and such.
There is a kit at alternatorparts.com called the ERCK kit that will by-pass the computer and put your vehicle back to the way dodge made them prior to 1987 where it had a separate voltage regulator The ERCK kit is easy to set up and gets the alternator control out of the computer.
 
#32 ·
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