Hello I have this very weird issue with my 99 v10. When ever it's cold and has sat for a while it will fire right up and run perfectly, and has a steady 14.5 volts at the battery. Once it's warm the voltage will Cut and go to 12 and within 30 seconds the truck will spit and spudder until it finally dies and will Not restart until it is cold again.
Could this be my voltage regulator in my ecm? Or a battery temp sensor going haywire?
I'm stumped and need ole faithful back! Any ideas are greatly appreciated.
I have replaced
Alternator
Alternator cable
Battery
Battery terminals

 

Mine will do that occasionally as well. But, only when it is cold outside, and I have driven it for a bit. Never does it when temps are above freezing. Its a rather confusing problem. Idle will start dropping, and the the alternator stops charging. if I don't step on the gas a bit, to keep the revs up, it will eventually stall.

The question becomes, what is the cause, and what is the effect? Is the engine starting to run crappy because the voltage is dropping off? Or is the voltage dropping off because the engine is running crappy? Which happens first for you? Does the idle start falling off? Or does the voltage drop first?

 

For me I can watch the voltage drop and the truck will continue to run until the battery just can't sustain the truck any longer. Giving it gas will only drop voltage more and cause it to die faster. IF I can even get it to restart hot at all the alternator is not charging and it will then die again until I let it sit for a couple hours, once everything's cooled down again fires right back up and you got about 30 minutes until the whole issue repeats itself

 

Ive been told by the second Gen Cummins guys to put in a external voltage regulator out of a 89 and bypass the internal ecm voltage regulator. But to me that doesn't make sense they all say their internal regulator failed all together not dependant on heat

 

Heat-soak failure isn't unusual, and neither is the internal voltage regulator failing altogether, unfortunately. In your case, the external regulator *may* solve your issue. I doubt having the alternator tested will yield any meaningful results, unless they run it long enough to get hot.... Testing it on the vehicle will only show that it isn't putting out voltage...... so, that would be pretty much a wash. I have also seen failing batteries cause these symptoms...... Of course, the battery you can actually test, and expect results that are reliable.....

I *think* there is a walkthru for installing an external regulator, and including the PCM in the loop, so that it doesn't set various charging system codes........ Test the battery first though.

 

I work at autozone, I put the alternator on my bench tester ran it until It was hot passed perfectly everytime, (as it should its brand new) as well as my battery I put a load on it and passed.

I've replaced both the alternator and battery attempting to fix the issue and neither helped the issue at all

 

You don't mention putting the battery on a charger after the truck dies. If the truck shows low voltage and dies, and then later the same battery starts the truck then the problem is not with the battery or charging. The voltage drop is somewhere else, e.g. battery ground or connection to the PDC, PDC itself. A voltmeter is your friend here.

 

A battery temp sensor could cause that. As it could think the battery is charging when it is not ****ting off the alternator. Just food for thought