Erratic voltage drop as engine revs??

[mckee1710]

just noticed this strange voltage drop as engine accelerates. At idle, alternator pushes 14.5V, verified with voltmeter. At about 1500-2000 rpm, the voltage starts to drop erratically, bouncing around from 12-14. The dash and cab lights pulse with the drop.

I’m thinking voltage regulator (which I believe is within the alternator on these trucks?) or slipping belt. Anyone have any insight? Thanks in advance

 

[RawbDidIt]

For belt slip, check the belt tensioner. Should move smoothly and provide decent tension over the full range of motion. Also check the grooved side of the belt for glazing. You can also check the pulley on the alternator if it's anodized as you'll likely see some anodizing being worn off if the belt is slipping. Make sure the tensioner isn't bottomed out against the spring stop. As far as the regulator, you can pull the alternator and get it checked free at most auto parts stores. They'll check the output amps and voltage in a controlled environment to check the regulator.

Sent from my SM-G965U using Tapatalk

 

[RawbDidIt]

If the voltage is erratic you may also see the tensioner move significantly through the range of RPMs. Could be the wrong size belt, the belt stretched, or the wrong size pulley somewhere. Have you changed any parts driven by the belt?

Sent from my SM-G965U using Tapatalk

 

[mckee1710]

If the voltage is erratic you may also see the tensioner move significantly through the range of RPMs. Could be the wrong size belt, the belt stretched, or the wrong size pulley somewhere. Have you changed any parts driven by the belt?

Sent from my SM-G965U using Tapatalk

Just at idle both the tensioner and the belt itself oscillate, which has me thinking the belt is stretched/worn and needs replacing. I’ll start there and see if problem persists.

 

[RawbDidIt]

Double check your belt length. When I changed mine I had 3 sizes to choose from, all three were with AC as an option.

Sent from my SM-G965U using Tapatalk

 

[mckee1710]

Replaced belt and battery, problem solved. Truck runs noticeably better/smoother.

 

[RawbDidIt]

Replaced belt and battery, problem solved. Truck runs noticeably better/smoother.

Thanks for the update. Glad we were able to get you running right

Sent from my SM-G965U using Tapatalk