2006 mega cab 5.9 Cummins with 37.3 volts at alternator?

[Ryanritenour53]

So I thought I was getting a really great deal on a truck so I thought the batteries took a crap so replaced them then the crimp on the end of the wire from the alternator to the battery broke I twisted back up and now started the truck wire started smoking and I had 19v on my passenger side battery shut the truck off so I removed the alternator and took it to 2 different parts stores tested it 10 times on each machine passed every time it's a Bosch with the Chrysler logo some I'm thinking its original? But anyways I'm thinking that what I've read the computer controls the voltage regulator and charging system but you can add in a in line regulator and I'm hoping this will be my fix rather than buying a new computer or used than paying the dealer to program any suggestions? Thanks

[kzimmer]

Fix your wiring properly before you run the truck again. Proper sized cables with proper crimps. Don't twist those high current carrying wires together. Your alternator and voltage regulator are going to be very unpredictable until you get the wiring sorted out. Only when the wiring is in good shape, can you test it out again, and check to see if the voltage output is proper, or if your voltage regulator is shot. My bet is that it's fine. 

To add: If your alternator charge lead is disconnected from the rest of the truck, IE batteries, fuse block, etc., your regulator can't see what the alternator is producing, all it sees is low battery voltage. So it cranks up the field voltage to compensate, trying to produce more armature voltage. Everything needs to be terminated properly to perform a proper test. 

[Ryanritenour53]

The truck doesn't have a voltage regulator its built in to the ecm pcm computer 

[kzimmer]

28 minutes ago, Ryanritenour53 said:

The truck doesn't have a voltage regulator its built in to the ecm pcm computer 

 

Yes, it has a voltage regulator, and yes you are correct, it's built into the ECM or PCM. Same principles apply. The second gen trucks have them in the PCM too, and they can be damaged.

Edited February 10, 2020 by kzimmer
Clarification

[Mopar1973Man]

Fusible link in the harness can be fried. 3rd gens have a fusible link buried in the loom. No alternator fuse like 2nd Gens but have a fusible link that burns in two inside the loom where you can't see. 

 

Why I say that is the ECM is telling full field to charge at max rate but the alternato can't reach the batteries because the fusible link is burnt in two.

Edited February 12, 2020 by Mopar1973Man

[Tractorman]

I would also double check the reliability of the multimeter being used.  Test it on another vehicle with a known good charging system. 

 

Also, as @kzimmer has mentioned - wires just twisted together will get hot and smoke as the alternator will be charging at a very high current rate right after the engine is started (making up for high current draw from the use of the starter).

 

- John

[kzimmer]

4 hours ago, Mopar1973Man said:

Why I say that is the ECM is telling full field to charge at max rate but the alternato can't reach the batteries because the fusible link is burnt in two.

 

Exactly. That's where the 37.3 volt measurement is coming from.

[Rogan]

I've fixed a couple Voltage issues on some 2gen trucks when the ECM section was dead.  I've used IVRs inside the alternator ro rectify the problem.  I can get part number I used, if anyone's interested.

[AH64ID]

Alternator feeds the passenger battery and the ECM reads the drivers battery. If the alternator voltage isn’t making it to the drivers battery you will have an overcharge of the passenger side. 
 

The crossover cable is a common cause if the voltage is different between batteries. The fuseable link if the voltage is the same. 
 

Do not use an external voltage regulator, you have other issues to fix. 

[Rogan]

10 hours ago, AH64ID said:

Alternator feeds the passenger battery and the ECM reads the drivers battery. If the alternator voltage isn’t making it to the drivers battery you will have an overcharge of the passenger side. 
 

The crossover cable is a common cause if the voltage is different between batteries. The fuseable link if the voltage is the same. 
 

Do not use an external voltage regulator, you have other issues to fix. 

In my two scenarios, all cables were replaced, FL, Alternator, etc., and testing proved to be the ECM internal circuits.  

[AH64ID]

1 hour ago, Rogan said:

In my two scenarios, all cables were replaced, FL, Alternator, etc., and testing proved to be the ECM internal circuits.  

It can certainly be the ECM but that’s a rare occurrence compared to faulty cables. 

[Rogan]

I agree 100%.   But the other oddity was that both trucks I worked on were 2001s, both 04/2001.. 

[Mopar1973Man]

My first thought is the fusible link in 3rd gens are buried in the loom. Burns out and then you have an open circuit and ECM is applying full throttle to charge the batteries but power never reaches the battery hence the charge voltage would be 30 plus volts.