Hi, I've got a problem with my Dodge 1999 Ram Van 5.9l engine. Since few days in the morning after starting engine the voltage gauge stays at about 12v. I checked the voltage on battery and it was 12.3 - with running engine. I assume it means aletrnator is not charging.
However it starts charging after 15 minutes or so and charges until end of day, even when I stop and start engine again. Next morning the problem appears again. So it looks like it's not working on cold engine - ? Sometimes it starts charging when I'm driving, sometimes it starts when I switch engine on and off.
I was at the car repair shop, they said battery cables where in bad shape and cleared clamps. I had to drive there so engine was hot and they said it should solve the issue. But it didn't - no charging next morning.
I could just replace the alternator, but is there anything else I should check/do? Had anybody seen anything like this before? Thanks!

 

Pull the alternator, and have it tested when cold. The voltage regulator is actually part of the PCM..... so, either the alternator is having issues, or the regulator (PCM) is...... Temp related issues *generally* point to the PCM though.... but, test the Alt first. (off the van, on a machine.)

 

Before starting the engine cold, use a hairdryer to warm up the alternator. If doing this causes it to charge right away, or at least in much less than 15-minutes then it's bad. If it has no effect then the next day try again but instead of warming the alternator warm the ECM. If this solves the issue the ECM is bad.

 

Last December my 99 3500 w/ 5.9 and original alternator (16+ yrs) finally failed. It wouldn't charge at all and only drained the battery, luckily battery was under warranty, was bad too and was replaced free. Alternator tested bad on their machine so decided on a lifetime warranted reman alternator napa had in stock, they also offered a "new" with same lifetime, good thing!

About a month ago had similar issue as you only volts would rise to about 13 when driving, and only occasionally jump to just over 14 on the gauge then drop back. I also had noticed an electrical burning odor as well, and I know alternators get hot but this one seemed extremely hot to the touch. Any way, had it test both on and off my vehicle and both verified not charging, battery tested fine at 12.7. Only explanation I got was diodes going bad... was glad for the lifetime warranted and new alternator (well...reman).
From what I understand now is if you replace yours, you might consider going with the "new" as opposed to a re-manufactured. Cost is a little bit more but all has new internals rather than not knowing what you're getting.

just my opinion

 

Just another thought here...how is the belt and tensioner, any chance the belt is slipping when cold? That would keep the volts low until it heated and started grabbing again.