Alternator overcharges, stays hot hours after the car is off

[my126benz]

Hope I’m not out of line posting this in the Camry Forum. Since the Celica and Camry share engines and so many other components, I thought this might be a good place to post my problem since this forum gets more traffic.

Hi Guys

I recently replaced the engine and transmission in my 88 Celica GT convertible. The engine is a JDM 2.2 (virtually the same) instead of the 2.0 that was in the car. The transmission is an auto from a car in the junkyard. The car had been running exceptionally well for almost 900 miles. Then, a couple days ago, My batt light and brake light started coming on as I would approach higher speeds. I also noticed my volt meter pegging, indicating an overcharging alternator. Also the car would not start without a jump. Took the car first to Autozone to have the battery and alt tested. They said it checked out. Then I went to advance and they told me I had a bad battery. I went home and took the battery out and went to another AZ to turn it in (3 year free replacement from AZ) and they tested it and told me it was fine. Next I went to yet another advance and they also to me it was fine. That night I noticed that the alternator was still hot even though the car had been off for several hours. So I took the alternator out (also covered my warranty at AZ) and took it down to have it tested. It all but blew up the second they started the testing machine. Sparks and smoke etc.
So I was issued a new alternator and I installed it. The car continues to have the same problems. I took it to the AZ and the battery, starter, and alternator tested fine. When I give it some gas the volt meter says it is over charging. The car has also been off for several hours and the alternator is hot to the touch. I am about to pull the neg. battery cable.
Does anyone have any ideas on what to check next? Is there a sensor that tells the voltage regulator what to do? Is there any particular thing I should check?

Any help would be very welcomed

Thanks

[lee777]

Buy or borrow a voltmeter to check your charging voltage.
Should be between 13.5 to 15.0 vdc.
A high voltage will soon ruin your battery.(boil it dry)

[my126benz]

Yes, that was my next step. Im away from home at college and I don't have all my tools. Should I check the voltage at the battery posts while the car is running? Also I have let the engine completely cool and yet the alternator is very hot, as if its been running for hours. What would cause the alternator(both old and a new replacement) to draw current while the car is off?

Thanks for getting back to me.

[lee777]

Yes, check at battery posts with engine running.
Next time you park your car, remove negative battery cable to see if alternator is
cooled down in half an hour.
Internal short in 2 alternators is puzzling?

[drugal]

You could also try unplugging the connector on the side of the alternator while leaving the negative battery terminal connected. This plug is what runs the IC Regulator in the alternator.

If the alternator cools down normally with this unplugged, I would suspect that the regulator is being powered at all times and draining the battery, which would explain having to use jumpers to start. The alternator has an internal fan that spins with the pulley while the engine is running. If the regulator is powered while the fan is stopped, it could stay warm.


The regulator should also have a sensing input, and if that connection is bad it'll tell the alternator to run at full-field (~18V or more). Find a wiring diagram manual for your car, or maybe a 5S-FE Camry, and carefully inspect/test all the wires leading to the alternator.

It might be different on a Celica, but here's a description of that connector from a 2.2L Camry:

"S" (Pin 3, white wire) - Sense line. It will eventually make its way back to the battery through several fuses. If this line is bad (corrosion, broken wire, blown ALT-S fuse), the alternator will overcharge, trying to compensate since it is not sensing enough voltage. Disconnect the battery, and check for continuity of this pin to the positive battery terminal and the alternator terminal. Both should be very close to 0 ohms.

"IG" (Pin 2, red-blue wire) - Supplies power for the regulator from the Gauge fuse. Should be 0V when the car is shut off, 13-15V when turned on.

"L" (Pin 1, yellow wire) - Goes to the charge warning light.

[my126benz]

That's such good information. I appreciate it. When I don't have a paper due I'll check that out. It seems to make the most sense. The voltage regulator is pulling power even with the car off.

Thanks for the good info!

[white90dx]

If the car wiring checks out, go get another alternator. Rebuilt alternators have a very high failure rate.

Good luck!

-Charlie

[my126benz]

Does anyone know how the voltage regulator senses that the battery is charged and turns off? Is there a relay that turns it off? I think my problem is that that circuit is staying open and making the volt. reg. stay on all the time.

Thanks

[lee777]

http://www.celicatech.com/imagearchi...20diagrams.pdf

If the wiring diagram in above link applies, alternator should have 2 white wires, one black/yellow
and one yellow wire, a total of 4 wires at alternator.
Blk/Yel is hot in Run and Start, Yellow is hot in Run.
If either is hot (voltage present) with key switch off, could be faulty ignition switch.
Regulator is solid state and appears to be built into alternator.

[my126benz]

Thanks Lee! I'll check it out

[my126benz]

An update.

I switched the alternator out of my gf's 90 Camry DX into the Celica and viola! The problem went away. I took it back to AZ and they would not give me another one because it tested "good". I explained to them what I had done and they told me to go to an electrical shop. I did and it they discovered it was overcharging. I went back to AZ with that info and they still argued with me until I asked "Why would i fight so hard to turn in an alternator I got last week if it was good?" They finally gave me another one and the car runs fine. So apparently my old alternator went bad and started overcharging and I got a new one that had the exact same problem. Go figure

Thanks so much for the help!

Phil

[fredk]

the voltage regulator in the alternator is stuck on, new alt time