Contour Enthusiasts Group Archives Forums General Troubleshooting intermittent excessively high voltage from alt

My alternator has been putting out an excessive amount of voltage intermittently the last couple of days. I just installed a 200 or 250 amp (I can't remember which) alternator from excessive amperage 2 weeks ago. The 3 wire harness was the typical ford alt harness and did not fit with my stock wiring, so I bought a new connector and wired it in. I don't believe this is part of the problem, but 2 of the wire colors were different, so I just matched up the wires location with respect to the factory wire harness.

My alternator seemed to work good for a couple weeks, but recently it started giving way too much voltage. My stereo measured 15+ volts (only measures up to 15v max) but it seems like it was more than that. It was enough to blow my head lights and a small 12v inverter. It also caused my gauges to stop working/go crazy during the over voltage situation. The problem seems to only happen at low rpm around town driving. If I keep the rpm's above 3,000 it never happens.

I was convinced it was a short somewhere. I thought that one of the sensing wires off of the 3-wire connector had been rubbing up against some metal somewhere. I took off the wheel last night and played around with some of the alt wires. I couldn't see anything wrong, but I couldn't see in there very well either. After moving those wires around last night and driving today, the over voltage problem hasn't happened sice (yet).

I have already performed the Ford TSB for the "flickering lights" problem. (relocating the voltage sense wire directly to the positive output terminal of the alternator)

Does anyone have any ideas about what I should check?

My car has been driving bad too (revving to 3,000 rpm in neutral while slowing down), but I imagine that is probably related to the voltage problem as it seems not to happen anymore when the alternator problem subsides for a while.

Thanks for the help

Maybe defective Voltage regulator or maybe the "flickering lights" TSB is only for stock amp (130) alternators.

thanks for the suggestions. The TSB remark gave me an idea to check the connection where I tapped into the alt output wire. I just cut the sense wire and relocated it to a better place that makes a much better connection.

The problem didn't come back for a while so I thought that it did the trick, but to my surprise it started doing it again yesterday while I was idling for about 15 minutes.

When the problem is happening it seems to be directly related to the engine RPM. It happens the most at idle. If I drive on the highway and keep the RPM's above 3K it never happens. Also, if the problem is happening, it stops immediately when I rev above 3K RPM.

Does it make sense that it happens only at low RPM?

as a side note, when the alternator is not giving excessive voltage it does not stay at a constant 14V. Sometimes it only gives 12.2, sometimes 13, sometimes 14. Shouldn't the output voltage stay close to 13.8 or 14 all the time?


I'm wondering if I might have wired the voltage regulator wires wrong, although I called the guy that built the alternator and he seems to think that if it was wired wrong, the problem would be constant and not intermittent.

The only other thing I can think is the defective voltage regulator as Tony said.


Anyone want to give some advice? Is there any reason to think it might be something else? I really don't want to pull out the alternator again if I don't have to.
Thanks

If you do end up taking it out, you may want to do a modification of the TSB wiring fix as was done in our Duratec Maintenance FAQ

I'm not seeing a modification of the TSB, I only see the original one. What modification was done to the TSB?