bad alternator?

Rob_Bones

Rob_Bones

I H8T ULSD
Joined
May 20, 2007
Messages
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The truck has been having intermittent, pulsating electrical surges. It was having an irregular idle, pulsating head and tail lights and you could even feel the truck lurching while idling across a parking lot. After reading around the interweb, it was suggested that it may be a bad battery. Sure enough, the driver-side Interstate battery was bad. After it was replaced, I put a volt meter on the driver side battery-cable-terminal and it reads 15.15-15.30 volts, with the headlights on (same as the other side battery) at idle. Also at idle, with the headlights off, it generates 14.2’ish. Is anyone else seeing high volt reading(s)?
Thanks for the feed back.

-Rob
2008 Big Horn 2500 6.7L G56 4x4
 
Possibly a bad alternator, but unlikely since they don't usually fail by making to much voltage. But as you may already know, the 6.7 ECM regulates voltage internally, so might be something to look into...

Also, the common train of thought around here is to never replace only one battery, but both at the same time, even though only one may have a bad cell or doesn't hold a charge.

Good luck.
 
Definitely try two new batteries first. If one is bad the other is usually not far behind. Also make sure the connections are really clean.
 
To me, it sounds like the regulator is going. I bet if you measured it in AC, you'd see it's hitting ~70V. You can get a regulator off an older dodge truck to separate it from your PCM. A friend had the same issue on his 05.
 
As it turns out, the connection between the crossover cable and terminal on the driver-side battery was rusted/corroded causing a bad connection. Once the mating surfaces were cleaned, she sits right at 14.0-14.2 volts.
 
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