Thank you in advance for any help and suggestions. I feel like a dog chasing my own tail at this point. Quick rundown of what is happening. For the last few years I have had an annoying voltage issue where at cold start the alternator bobs back and forth between charging and not charging for a few minutes until it finally decides to charge, also at WOT and only after about 5K RPM my voltage drops significantly. Like below 12 volts. This obviously hurts top end performance. I had contributed this to my alternator being pissed on by my leaky power steering reservoir. I finally got around to replacing my power steering pump and cleaned the hell out of my alternator (truck alt) the car was still having the same issue. So I bought a reman ACDelco truck alt thinking my alt was just toast from the leaking PS pump. I swapped it last night. This morning when I did my first start since replacing it the voltage shot right to 14-15 volts on cold start and didn’t dip. I thought the issue was fixed so I got on the highway to see if the voltage would drop under load and low and behold it’s still there. A couple years ago I replaced the exciter wire but maybe It’s bad and needs replaced again? I have checked all the grounds and everything seems solid. I even added another ground wire to a bolt on the head. I have an upgraded walbro 255 fuel pump with Hotwire kit. I don’t know what is causing this at this point and I need help troubleshooting. I know at this point it’s not the alt. Any help is much appreciated, I feel like whatever the issue is this alternator is on borrowed time. This is the 3rd alt I’ve put in the vehicle in 4 years (all high amp alts) I had contributed this issue to my power steering pump but now I believe this is something else causing my Alts to go bad. I have seen other forum posts on similar issues but nothing exactly like my situation.

Edit: I also put in a new belt tensioner (to rule out belt slippage) and replaced the serpentine belt out to rule out bad belt.

 

Are you sure the gauge isn't bad?

 

I am battling a similar issue.

My voltage drops to 11.25v at WOT.

I upgraded to the 145amp truck alternator and replaced the 4 pin connector, didn't fix it and no improvement

Just finished with the big 3 wiring upgrade(using 2 gauge wire) last night. Didn't fix it and no improvement.

When I installed the dual fuel pump assembly, I ran the power wires to underhood fuse block because the wiring supplied with the kit was no where long enough to get to the battery.

I'm going to run the fuel pump wires to the battery this afternoon. I wouldn't think those pumps could be pulling enough voltage off that junction block to drop the 2 volts, even if that was the problem I think I would see some sort of improvement with the upgrades.

Obviously my problem is elsewhere.

I didn't mean to highjack your thread, just wanted to let you know I am as frustrated as you are.

I'm logging system voltage in HPtuners, BTW. It shows about .5v lower than what the meter shows at the battery.

 

Total shot in the dark, I had an elusive balancer bolt loose on a C6 vette that kinda sounded like this. Had voltage drops (and power steering choppiness etc) only when hot, but also had visible oil drips at balancer.

Since nobody else replying I'll offer this. If you can get to where you dupe the symptoms, try using a scope to watch amp draw (amp clamp probe) and also monitor voltages at all the key points while it's happening, that's probably where I'd go next if it were me. Either the power isn't being provided intermittently or something it eating it all. Figure out what the actual problem is then fix should become obvious.

 

I have a scope and I'm going to testing things.

The wire in the flat 4 pin connector, I "think" it comes from the PCM. Does it just supply 12v to the alternator to excite it?

 

Does it drop voltage on ANY WOT or above a certain RPM. You could be exceeding the rpm rating of the alternator.