The factory alternator guag eon my dash is behaving oddly. THe needle always reads above the middle line and wiggles around. The needle also goes higher as the RPMs increase. THis started about a week ago. One alternator already burned out a field so it only made 12 volts at idle, and I don't want to burn out the new alternator I just put on. THe voltage regulator is a known good unit.

Does anyone have any idea what this might be? The new alternator puts out 14 volts at idle, but hat is what it is supposed to do right?

Battery with bad cell.........

Try another battery and see what happens.

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Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

If your cranking speed is notably slow and you get severe dimming of lights at idle, then yes, a dead cell in the battery is probably the cause. But, your symptom is also exhibited where the voltage regulator is faulty or has lost its ground.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

No, the lights stay nice and bright and cranking is no problem. I wil double check the voltage regulator ground and try a different voltage regulator.

Would the fact that the van no longer has the lean burn computer effect this issue?

Do you have good connections, esp. at the battery terminals. Terminals that look fine may be bad. This problem drove me nuts on our old Ford farm truck until I finally traced it down to a bad terminal.

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82 D150-225/727
02 Dakota-3.9/5 speed
87 GMC C7000-8.2 Detroit Diesel/5+2

Lean burn computer's absence will have no effect here.

Is it a new or used alternator you installed...?

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Both alternators I have installed have been used.

Blown diode(s)?

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82 D150-225/727
02 Dakota-3.9/5 speed
87 GMC C7000-8.2 Detroit Diesel/5+2

Yep, a shorted diode can also cause these symptoms, but usually it is accompanied by a very audible electrical whine from the alternator, especially above idle.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

I've had diodes both short and open, brushes wear and chip, and field windings go partially bad - all left the alternator partially working, but not well. None of the problems made any noise I could hear. Bearings going bad made a lot of noise.

Many places offer free alternator testing, but when I took mine to Advance Auto parts they had no idea what they were doing. The Mopar alternators are easy to take apart and fix.

Here's more grist for the mill: the guage on the dash seems to have settled down a bit. THis morning on the way to work it would still bounce a little at idle, but one the RPMs increased it would hold steady slightly above the middle line on the guage.

I still have the two other alternators I tried before and I might try rebuilding them in the (distant) future.

You can remove the alternator and test it on one of those machines at autozone or any other part store.

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82 D150-225/727
02 Dakota-3.9/5 speed
87 GMC C7000-8.2 Detroit Diesel/5+2

You might want to recheck that regulator while your at it. Spikes from the alternator can make them go wonky.