3.4 auto voltage drop when shifting into reverse/drive.

Installed the John Deere Denso 150 amp alternator. It’s new and not a reman Denso or Chinese reman. Truck seems to be operating similar to before.

This all makes no sense to me and this thread has just turned into rambling from myself. Truck is charging at 14v once it warms up with the HKB voltage regulator installed. ~13.6v with it not. It drops to 13.9v if I have my headlights and AC at max and shift into gear.

Not in range for my AGM battery. And maybe after all of this I don’t even care.

 

I feel your pain and frustration strange intermittent electrical problems get to all of us.

I can only hope the problem opens completely and is simple to find.

We do the best we can!

 

I’ve been driving the truck all afternoon at 13.9-14.1v. Stoplights at ~550rpm it goes to 13.8v but the computer was just reset and it’s not running normally yet.

I’m running the upgraded battery cables and separate 150amp alternator fuse with no issues. Wish I could bump the voltage up a bit for the AGM but this is fine.

 

Glad you're making progress.

Thats about where mine (2nd gen) settles out once warmed up and running a while. A bit low for AGM yes, but IMO thats better than being too high during a cold start. May not be an issue for you in TX, but worth keeping in mind

 

Maybe I missed it, but have you tried swapping out to a different battery to see what happens? Just looking for things that may not have been tried.

 

many things have been swapped batteries, alternators and cables

 

Yeah, I saw where cables and alternators were swapped, just didn't go back and search for whether a different battery was tried. This one is a booger, but seems related to the AT circuit somehow. My first thoughts were just that the drop in engine speed caused the alternator output to drop, or maybe something in the reverse/brake light circuit. The spike to 16V makes no sense if it happens on different alternators, which is why I was wondering about the battery, although even that would seem odd.

Anyway, hoping OP gets it sorted. It was 90 degrees here at 9:30AM, not good troubleshooting weather.

 

Troubleshooting this shirtless in my garage in the 105-115 degree heat has been less than ideal. Truck seems fine now with this Denso John Deere unit and I've determined the OEM and the Mean Green are bad. They both show signs of a failed voltage regulator somehow. The OEM just sat at 15v+ while the Mean Green fluctuated a ton and occasionally shot up high too.

I'm going to just assume the Denso Suzuki alternator from my other truck acting strange (voltage fluctuations) was a fluke between swapping cables, batteries, and changing out alternators like 5 times the day I tested it.

 

Good luck moving forward .

You just have very poor luck with alternators .

Why they all seemed to fail in a short time.

Planning to make them work again?

 

I could try Chinese voltage regulators from Amazon. Toyota ones are like $100+

 

I have a Good source for Electrical Parts I need to find it.

 

After all the issues you had in this thread you're considering using cheap junk parts?? Good luck

 

Just listing out my options. Both alternators are in the scrap pile in my backyard. No sense in fixing them when an OEM Toyota alternator is almost the same price as a regulator.

 

I know you seem to be getting closer with this, but I have two thoughts I’ll share anyway.

First, the odd and intermittent nature makes me think that there is a connector with no / low pin tension, AKA pin drag. I’m thinking mainly of the connector onto the regulator, and to check it, you need a male connector pin the same dimensions as the ones in the regulator. You should feel a definite drag pushing the into / pulling them out of the female terminals in the harness connector. Now get your mind out of the gutter so we can move on to the second idea.

This would apply more to the low voltage part of the issue, but lets be sure that the belt is in good condition, not oily, is routed correctly, and tensioned correctly. And be sure the idle speed is in spec.

 

I'm going to just call this one solved. I appreciate all the input but I don't see the belts or belt routing being an issue. Nothing is oily/dirty on this engine because I just had it pulled for corrosion causing 4-5 small head gasket leaks at 140K. Engine rpms look perfectly normal now that I have some miles on the truck post-computer reset.

If the voltage issues returned I'd definitely look at the alternator connector.