Electrical Diagnostic Question

I recently picked up a 100A Denso alternator from the junkyard. After replacing the rectifier, brushes, and voltage regulator it works great. The only weird thing about it is when coming to a stop the RPMs drop (almost like it bogs) and the voltage drops for an instant before returning to ~14v. This happens more if the headlights are on or the A/C is running. I'm not sure if it's problematic, but I'd like to troubleshoot it for peace of mind.

My first thought is something with the external lighting circuit is the culprit. Anytime my parking lights or headlights are on the "bulb failure" dash light is illuminated and the voltage drops, but all of the lights work. I've read that checking each bulb circuit for voltage drop will help to diagnose the issue but I've never been able to get clear instructions on how to check that. I've got a power probe (which is a kickass tool for testing relays and individual components) and good DVOM which I've used to wire in headlights on a golf cart, and basic moped/scooter diagnostics. Any tips or methods to narrow down this issue?

Sounds like an engine problem, made worse when more accessories are getting power from belts. voltage drop seems more like symptom of engine bogging than cause

Belt slipping?

I would guess that the TPS is not properly calibrated.

In fact, I would guess that about half of the people on this site have improperly calibrated TPSs.

edit:// Sorry to sound so... IDK. Anyway, here are the steps:

- Make sure the throttle is closed.
- Loosen the screws holding the switch to the throttle body.
- Turn it slightly towards the cylinder head.
- Turn it slowly back towards you until a click is heard.
- Tighten the retaining screws

When you get this right, you'll hear a click every time you open the throttle.

HTH

TPS is set correctly. That was something I made sure off when my idle was high. I'll check the belt, that's a possibility. It's just odd that the problem DOESN'T happen if I come to a stop without my headlights on.

One could put a current clamp on it and see if there is low output.

I would also do a voltage drop test one the positive and ground of your alt cables and also on the battery cables.

That low drop before idle on these engines is almost always a sneaky vacuum leak somewhere. It leans out low rpms and causes too much drop and then it comes up to idle.

Examples I have experienced on B230 type engines are the injector seals, intake manifold gasket under the runners, and the various small hoses that run to stuff like the charcoal canister. Also if any of the turbo air handling hoses have the oily saturated look to them. They will have a vacuum leak affect on the way the engine runs causing the kind of issue you describe. In addition don't forget about the flame trap hoses which also cause a vacuum leak if they are cracked or broken.

I agree that low idle speed/stumbling/stalling could easily be misidentified as a low charging issue.

Make sure t body is setup correctly, no air leaks (smoke test), and TPS is adjusted correctly.

Vacuum hoses should be good as I replaced all of them with silicone when doing stage 0, but I'll double check for any vacuum leaks.