Battery Charging Issue

[BucksCo]

I replaced the alternator brush holder on my '99 the other day after a few weeks of the battery light lighting up then going away. The brushes were in bad shape, gunked up and replaced. Everything has been fine until this morning when I started up and my battery voltage was at 11.9v and the light came on again.

I turned my obdII app to monitor the volts and a funny thing happened when I stopped for a traffic light. I was waiting for the light to change and it felt like something kicked on and the battery voltage went from 11.5 up to 14.2 quickly. The 4runner kinda vibrated a little bit (I'm not sure if that's really a good description, but it reminded me of when a house heater kicks on).

Any ideas on what's going on? The battery is about 2 months old and I believe the alternator is original. It's a Denso unit.

 

[LittleCaesar]

Check you wiring to the alternator but if the voltage regulator is toast, then you many want to look for a Denso remanned or one from the dealer.

 

[gamefreakgc]

I'd also check the ground wires. There's a few to check, engine block to firewall on the back of the passenger's side cylinder head, battery ground to fender (negative battery terminal) and if you can reach it, there's also a ground wire to the engine block on the lower engine harness that also connects to the alternator. I think the alternator uses that shared ground.

Anyway those are three to check. Look for firm connections with no movement and no corrosion or grime. If yes then remove, clean, and tighten.

 

[BucksCo]

I'd also check the ground wires. There's a few to check, engine block to firewall on the back of the passenger's side cylinder head, battery ground to fender (negative battery terminal) and if you can reach it, there's also a ground wire to the engine block on the lower engine harness that also connects to the alternator. I think the alternator uses that shared ground.

Anyway those are three to check. Look for firm connections with no movement and no corrosion or grime. If yes then remove, clean, and tighten.

Thanks. I replaced the battery ground when I replaced the battery a few months back. I wasn't aware of the other 2 grounds. I'll take a look at those.

 

[TheDurk]

Thanks. I replaced the battery ground when I replaced the battery a few months back. I wasn't aware of the other 2 grounds. I'll take a look at those.

Also take a close look at the plug connector on the alt. Those wires are thin and break easily. You may have killed a weak one while working on it. To me, it sounds like a connection issue somewhere. I have never seen a regulator die and then come back to life periodically. They die, they die, I think.

Don't forget to check the Alt-S fuse, but I doubt that one because those don't come back to life, either, except in rare cases where they are semi-burnt. Still worth checking. Me, I'd just swap it for fun. It may be 18 years old.

In fact, best practice is to check for battery voltage on the red/blue and white wires at that alt plug (key on). Don't worry about the yellow-green as that is the dash light and that seems to be working.

 

[SaulG]

Brushes may have bedded in , what shape was commutator in?

 

[DaMonkey]

I have never seen a regulator die and then come back to life periodically. They die, they die, I think.

YouTube

 

[Kanoe]

That sounds like the symptoms of worn out brushes, but I know you just replaced them. I wonder if one of the new brushes is somehow hung up in it's groove and not advancing properly. Try tapping the alt. when it happens again to see if it kicks back in.

 

[WWRD99]

I rebuilt mine a couple times until the comutator...the spot the brushes ride on looked like the grand canyon...the first set of brushes I put in didn't work so I got another and it worked for about 3 years..maybe you got a bad set??...got 18 years out of mine though...did the gm swap since.