Toyota: 89 GTS Overvoltage when RPM exceeds 4000

Salutations,

Today on the hiway my little GTS had problem. Without warning, my
voltage meter suddenly pegged to the high end of the scale. The "Brake"
light came on as well.

Almost immediately I could smell the battery boiling over. But as soon
as the RPM dropped below 2000, it was like a switch closing; the
voltmeter returned normal and the "Brake" light turned off. For the
rest of the trip home whenever the RPM rose above 4000, the condition
would return like the flick of switch.

I managed to ease her down the highway a few miles to a gas station.
Under the hood, I could see that the battery had indeed boiled over
some. But it didn't look too badly damaged and was still holding a
charge. Nothing else seemed out of place or damaged. I revved the
engine high enough to cause the condition, but did not hear or see
anything in the engine compartment to indicate what might be causing.

A multimeter will should tell me what my alternator output is. But I'm
wondering where else I should look in case it's something else.

This is also supposed to be a "new" alternator. Is the AE86 predisposed
to this kind of electrical problem? Is this a textbook voltage
regulator failure scenario for this model?

Any assistance greatly appreciated!


Cheers,

Lucius

I think it's dead Jim,

My over voltage problem has now progressed to a non-starting problem.
Although, I believe I'm responsible for that.

Checking the battery with a voltmeter showed that even without the
engine running, the battery voltage was 13.5V Quite high. Running at
idle, the voltage was 13.9V and would spike to nearly 19V when the RPM
was over 4000.

Thinking of eliminating the possibility of a bad battery cell, I
disconnected the negative terminal of the battery while the engine was
running. The voltage on the leads did not change. But when the engine
RPM was brought up over 4000, bad things happened.

The voltage spiked somewhere around 22V. The windshield wipers toggled,
one headlamp flipped up....and I think there was an arc in the vicinity
of the alternator. The engine stalled, and would not re-start when the
battery was connected.

I replaced several fuses that had apparently blown. But still, the
engine will not start. It turns over fine, but doesn't seem to be
getting any spark at all.

It's now parked and waiting to be towed to the shop on Monday.



Lucius