Crackership

Hi all,

I've just gotten my new-to-me 3VZ-E 1995 4Runner back together and, have quickly noticed that the voltage creeps up from a pretty normal ~13V to a rather alarming ~16-17V within seconds of starting up. Before I go replacing an alternator, any ideas of things I should check?

Thanks in advance!

jerry507

Bad voltage regulator inside the alternator. Replacement is basically your only option.

Sturmcrow

Are you basing your reading off of the battery indicator in the cab or a multimeter on the battery? The alternator is supposed to go quite a bit above 12V, usually closer to 14V, as measured at the battery. I would not trust the gauge on the instrument panel as anything other than an estimate.

scope103

The good news is that the voltage regulator kit doesn't cost much more than a whole rebuilt alternator (huh? Hey, I don't set the prices.)

As Jerry507 says, you've got to be measuring it in the right place (I, too, pick "at the battery") with a meter that is correct. But if you've done that, pull the alternator out and have someone put it on a tester. You don't want to drive around like that; high voltage will ruin a battery in short order.

Crackership

I am taking the reading with a multimeter at the battery. I was pretty sure it was the regulaor - seeing as it's job is to regulate voltage - but I was just curious if there were any other magical little gremlins in this particular truck that could cause such things. I guess not. Wishful thinking anyway.

Thanks guys

Robert m

iTrader: (2)

make sure your alt wire isnt toasted after that much voltage. i had my alt wire get burnt at the fuse box right at the 80amp main fuse because my VR went out and was spiking to 18v.
i was loosing over a volt from the back of the alternator to the battery because of the bad wire.

Sdmeitzner

Any satisfaction on this? I've got the same kind of thing happening on my 78 p/u. Voltage starts out normal, but creeps up to 17 volts within a minute or 2 of starting. Also, if i turn blower n headlights on, it'll drop to 12, (lower than the battery voltage to start with). When i turn the accessories off, it takes a couple minutes for the voltage to once again reach unsafe levels.

New batteries, new alternator, new regulator.

Crackership

Sorry I never posted my resolution, I hate reading threads thay describe my exact problem and then never post a solution. Really didn't mean 5o be 'that guy'.

Anyway, shortly after my problem began, my alternator let all of it's smoke out and quit turning etirely. Thankfully, it happened in my driveway and not on the highway or out on a trail. Replaced the alternator and all has been well since.

RAD4Runner

What's unsafe? Normal Alt output ranges from 13.5 to 15.1 VDC depending on battery condition and temperature.

When you see "unsafe" voltage, do you get charge light on?
Does "L" output (yellow wire ) go from 12V to almost if not Zero volt?

Make sure the "S" (white wire from connector, not alternator screw post) wire is making good contact from the fuse block to the alternator terminal. If "S" terminal of alternator sees low voltage because of poor connection to battery, it will think that battery still needs more voltage an will increase it's output.

STILL, if output is still too much, regulator should fault out, bring "L" output low and cause charge light and brake error light to come on. Do you see above symptoms?

scope103

RAD4Runner -

Are you sure that a failed regulator will pull "L" low? It would be a good design if it did.

17v on the battery will quickly boil out the electrolyte and damage the battery ("over-charging"). If a reliable voltmeter on the battery reads anywhere near that high, I'd at least pull the alternator and have it tested, no matter what the "alt" light says.

RustBucket

iTrader: (1)

After I did the GM alt swap my first Advance Auto Parts remanned alternator crapped out 2 months in. First sign was a funny harmonic engine noise. Second was a slight smell of cooking electronics. Third my voltage went low at idle and high at higher engine speeds. Turned out one diode was bad.

RAD4Runner

I would think so. Yep, IF, and only IF, it were a properly designed system it should indicate any charging issue:

• No output,
• Too low an output,
• Too high an output

I'm hoping someone with over-voltage issue could answer the question ^^^ based on their actual first-hand experience. ... Does the Charge light come on when over-voltage is happening? Charge light on means "L" output low, causing negative side of Charge light (and brake light on first-gen 22RE's) to go low, causing charge light to come on.

Agree 110%.

But before doing that, I re-iterate (^^^) that Sdmeitzner should make sure
"S" terminal is getting accurate reading of battery voltage like I mentioned above.
Simple to test before removing the alternator or buying a new one.