Alternator diagnosis help (1 Viewer)

[MastiffDad14]

Factory alternator just failed last week. Driving home battery light illuminated voltage dropped from 14.4v to 13.2 volts when I pulled in the driveway. Checked it out the next day turned on the truck voltage was showing 13.8 when cold and hovered just above 13v when warmed up.

I ordered a denso reman, installed it Friday evening. Fired up voltage was back to 14.6v problem solved or so I thought, as it warmed up it would drop to 14.2v still great. While on a 1 hour trip I noticed the voltage went down to 13.5v battery light illuminated then a moment later my scan gauge is reading 16.9 volts! I pulled over stopped before it caused any damage, waited 10 minutes fired it back up and it's showing 14.3v. I proceeded with the drive and it went back to 13.5v with the battery light illuminated.

Turned the car on today and its back to normal again but if I drive for a bit it drops to 13.5v then periodically will jump to 16.9v. Did I get a dud?

I checked the wiring and alt s fuse. Put a multi meter on the alt a pin from the alternator and moved the wiring harness around expecting a possible short (voltage would drop or show 0v) but no dice. Any ideas are welcome.

 

[nissanh]

If you have the old alternator, replace its brush kit anf drive. Most remanufactured units are garbage.

 

[abuck99]

A legit DENSO reman (sold through a Denso authorized distributor, not Amazon) is basically all new components, its possible the VR was a dud but not likely. But your 16v+ is overcharging ( shouldn't ever go over 15v) so you might try what nissah suggested by replacing brushes in old alt and reinstalling it to see if your overcharging goes away. Did you buy Denso 210-0607 and from where?

As for the voltage charging range, normal voltage output 13.2~14.2. On the 130A alternator it starts higher and as the battery is topped up and electrical system is balanced, the voltage output will adjust downward towards low 13's. The fact that your battery light came on and you're showing higher than average voltages could also point to a bad battery, bad cell etc. Have you tested the battery for CCA?

 

[badlander]

I would check the connector plug on the alternator. It needs to be pushed on very hard to lock in place and if it wasn't it may have worked out and you are getting intermittant connections on the sense and or light terminals.

 

[atnolan94]

Voltage dropping to 13s when warm isn't that odd. I don't know that the alternator is your issue here. My truck at idle and warm sits at 13.4-13.5v with no issues at all. When your alt dies it will not read any voltage beyond the static battery.

As for the overcharge, again, not sure alt is your issue.

 

[nitteo]

i would check the connector plug or replace it entirely, just to eliminate that possibility

 

[MastiffDad14]

I wanted to add, I have a voltage booster so all of my voltage readings are really approximately 0.5v higher than a truck with out. I have replaced the booster with a regular fuse and the problem persists as stated readings are just 0.5v lower.

 

[atnolan94]

Ok so really you're high 12's. Yes I'd say that's concerning. I have heard like 1 in 4 or so denso remans is no good. I bought from toyota (which is basically a denso reman) and luckily no issues. Was like $120.

 

[94SRUNNER]

Have you taken it to get the battery and alternator tested?

 

[abuck99]

I wanted to add, I have a voltage booster so all of my voltage readings are really approximately 0.5v higher than a truck with out. I have replaced the booster with a regular fuse and the problem persists as stated readings are just 0.5v lower.

Remove this and see where you end up. It's probably causing the issue. I wouldn't recommend adding this to the electrical system; the charging system is regulated by the ECU which works with the alternator VR to compensate charging requirement based on load/drain, rpm, heat etc. Putting something inline to fool the ECU to signal the VR to output more charge is probably negatively impacting your charging system. (Just a guess)