Battery not charging .... Sometimes??

jeffro312

Original poster
Member
Oct 4, 2012
442
East Haven,Ct
So other day start my truck light comes on says battery not charging. Then soon went off. So I connected torque app to keep eye on voltage. While truck is on and it is charging at the obd2 it's reading 13.5-13.8. Later while driving I hit gas to pass it down shifted and bam voltage drops to 10.6-11.3. Then my hids flicker because that's what they do when truck is off. That lasted a minute then jumped back to 13.6. Then normal cruising 65 on highway does it again. This time light for battery not charging comes again.

I want to jump and say bad alternator but I assume once alternator is bad it's just bad won't charge at all.

Another thing to add related or not I dunno but couple times I heard that shop vaccuum noise I usually hear at start up (not all the time). But was while I was driving and only for brief two or three seconds


Any help before I buy an alternator would be great thanks guys
 

kickass audio

Member
Aug 25, 2012
955
How high were your engine RPM's at that time? I have an upgraded alternator and it has a smaller pulley than the stock alt and as a result, if I go above 4300 RPM, the alt shuts off because it is spinning way too fast.
 

jeffro312

Original poster
Member
Oct 4, 2012
442
East Haven,Ct
I have a stock alt as far as I know. And it happens when I start truck at idle and random highway driving around 2k. Down shift probably around 4kish
 

kickass audio

Member
Aug 25, 2012
955
Probably some belt slippage then. Check your belt tensioner and belt condition. If its glazed or cracked, replace it.

For it not charging when you first start it up and its cold, thats normal. the PCM commands the alt to stay off until the engine has some time to get a steady idle speed on cold starts and then it kicks on the alternator.
 
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jeffro312

Original poster
Member
Oct 4, 2012
442
East Haven,Ct
No I know but that's when I see the battery light come on and display says battery not charging then once I go it's fine.

I will check belt.
 

Sparky

Member
Dec 4, 2011
12,927
Alternators can be unstable like that, they don't always just totally quit. My alternator on my old car did exactly that.
 
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c0a8l0v6i8n9

Member
Mar 6, 2013
93
I had an alternator on my s10 blazer that was working fine. One day I floored it and at like 5000 rpm the alternator took a dump.
 

jeffro312

Original poster
Member
Oct 4, 2012
442
East Haven,Ct
Well new alternator and all is well. The battery light finally came on and stayed on battery voltage dropped to 6.2 volts truck still ran but nothing else worked. Once I out it in park couldn't get it out until hooked up my jump box. Had to change alternator in parking lot I got stuck in. Took 35 minutes in 20 degree weather tools needed a 10mm socket and a long and short 15mm socket and strong fingers on left hand for that bottom bolt. And the shop wanted to charge me almost two hours hahaha. In there warm garage with every tool you could possibly need
 

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