Weird Charging Issues. Have to Rev truck to start charging.

[Pooble]

Replaced battery and alternator after the truck died after a 5 hour drive a month back.

i had to replace the battery and alternator since the truck was holding 10.5 volts on the old batt/alt and i was 5 hours away working in another town so i had no choice to replace both to make the 5 hour drive home.  now the truck does this weird thing were it will only start charging once you hit a certain rpm range.

 

ive cleaned the grounds under the driver side on the frame rail.  The one under the rad support to battery .  Replaced the broken hood to body ground. Checked the body to block ground strap and now the truck will ONLY start charging once the RPMS hit 4-7k and then the truck runs completely like normal and holds voltage at any rpm. untill the truck is turned off and you have to repeat the process of having to rev/drive the truck up to 4-7k rpms and voltage jumps to 10v to 14.5v.

i don't mind doing this when its warm lol since its a quick fix but its not ideal and the problem is winter is coming and regular -20c to -30c temps soon so i don't want to be hitting those rpms to keep the battery alive when the truck is still warming up.

 

ive read that 2005 models have some kind of module on the ground. just wondering if anyone has experienced this weird symptom .any ideas would be helpful, thanks guys. 2005 gmc sierra 1500 4x4  

Edited November 22, 2023 by Pooble

[richard wysong]

Sounds like the circuit to turn it on is bad, either internally or from the ignition . The alternator is self exciting when you rev it up, normal operation,If the original alternator worked normally it is probably just a bum alternator. Do not try jumping the 2 wire plug with 12v, it will fry the regulator, been there, done that

[Pooble]

6 hours ago, Pooble said:

i have another alternator off my 03 sitting on a shelf  ill try a quick swap.

 

 

[Pooble]

Seems to a bum alternator, something i didn't expect since it was new. Was able to get ahold of napa in the other town and get an email of my receipt and get a new one to try out.  this one is holding 14.6 the second the truck turns on now. thanks a bunch