97, bouncing battery gauge. Alternator? (1 Viewer)

[ramblinman]

Hey folks,
Got an electrical issue that I’m diagnosing and it’ll probably be a simple one to you old heads who’ve seen it all.

Tried to crank up my LC the other day and it was dead. I assumed someone didn’t close door all the way so put a charger on it, and cranked up after 10m. Ran my son around to the library close by but waited in the truck with it running. On the way home I noticed the battery gauge was a little bouncy, especially with the turn signal on.

Get back home and checked the voltage across the battery, reading anywhere from 12.5v to 14.2v with truck running. I disconnect the positive terminal, thinking that’s a good way to see if alternator is working and see around the same.

Leaving the battery disconnected I turn on the emergency blinkers and the truck turns off.

Seems like that means I’ve got a bad alternator. Could that also drain the battery when it’s turned off?

 

[LandCruiser65]

Have an auto parts store nearby? I would have them test your charging system. Definitely sounds like an alternator tho. Stick with OEM too.

 

[gummycarbs]

I disconnect the positive terminal, thinking that’s a good way to see if alternator is working

It's not, and that's a bad idea.

Don't Disconnect the Battery with the Engine Running

Never disconnect the battery when the engine is running

www.troubleshooters.com

Get back home and checked the voltage across the battery, reading anywhere from 12.5v to 14.2v with truck running

The stock charging system isn't ideal, but I don't think it should be as low as 12.5V at idle. Most likely your alternator is bad. I would order a remanufactured Denso from RockAuto. Or, if your alternator is original *and* you happen to be lucky enough to have a local rebuilder, get yours rebuilt.

The stock setup will show some bounce with the headlights and turn signals on, but I don't believe it should go as low as 12.5V.

I suppose it's also possible that your battery is bad, pulling the voltage exceptionally low at idle. Auto stores can load-test your battery. You'll need to know the amp-hour rating of your battery.

 

[robnicko]

it could just be the brushes that are worn down and maybe sticking. your reading anywhere from 12.5v to 14.2v with truck running is a good indication that they may be worn and intermittently not making contact causing the vast fluctuation. did you not get any red lights on your dash when this happened?
Mine played up a few weeks back and I replaced the brushes and all is good now. The old ones were the original and over 500,000km so definitely in need of replacing as they were very worn down

this vid is excellent and shows how easy it is to do once the alternator off

 

[jonheld]

If the battery is a standard led/acid unit and you ran it flat, it's done now. A severely discharged battery will not recover.
And 10 minutes on a charger along with running some local errands will not charge a depleted battery even if the battery is in good shape.

 

[ramblinman]

It's not, and that's a bad idea.

Don't Disconnect the Battery with the Engine Running

Never disconnect the battery when the engine is running

www.troubleshooters.com

The stock charging system isn't ideal, but I don't think it should be as low as 12.5V at idle. Most likely your alternator is bad. I would order a remanufactured Denso from RockAuto. Or, if your alternator is original *and* you happen to be lucky enough to have a local rebuilder, get yours rebuilt.

The stock setup will show some bounce with the headlights and turn signals on, but I don't believe it should go as low as 12.5V.

I suppose it's also possible that your battery is bad, pulling the voltage exceptionally low at idle. Auto stores can load-test your battery. You'll need to know the amp-hour rating of your battery.

Wow, I had no idea about pulling battery connection being so bad. Thanks for that!