Inconsistent voltage, Not very electrifying Options

[iankarr]

Hi Guys,

Trying to sort through a puzzling situation. My car started bucking like a bronco(D-jet) and I noticed that the voltage was super low (like 10). I fortunately made it home. Changed out the voltage regulator with one I had in my bin and everything seemed to be fine. 13.5 when running, no more bucking.

Now I'm seeing that the voltage is inconsistent again. Sometimes it's 13.5 when running, then it dips to around 12, then comes back up. Occasionally the red light will come on for a few seconds, even when running at 3K rpm. When I put the headlights on, the idle drops by 500rpm and stumbles.

The belt is tight and the alternator was (supposedly) rebuilt recently.

Anyway...my thinking is it can only be one of four things:

– Bulb in the cluster (unlikely, but possible). I believe it's stock.

– Voltage regulator

– Alternator

– Battery

Do you guys have any simple tests i can run to eliminate any of the above before I just start throwing parts at this? Other thoughts?

Thanks!

[Superhawk996]

HF battery load testers are dirt cheap and are an easy way to test the battery to verify it supports load. This will help rule out battery as a potential problem.

Beyond that it sounds a lot like a failing alternator given the fact that you have tried two voltage regulators and that your light is illuminating at 3k rpm (verifies bulb is working). Similarly when you add the large load of headlamps, it seems you’re not able to support that load without dropping voltage.

You can full field the alternator to verify output. However if alternator is fluctuating intermittently you probably won’t gain any info unless you can full field it when voltage has already dropped.

Check B+ terminal at the alternator and make sure you have a solid connection. Loose terminal or poor connection will lead to flaky behaviour as SirAndy noted.

Likewise, if you painted or powder coated the fan shroud make sure you have metal to metal contact between alternator bracket and fan shroud as well as clean connection between fan shroud and engine case.