Figure this alternator problem out

[tunabreath]

95 Subaru Legacy, 2.2L 4 cylinder.

Drive the car last night, turn the wipers on and notice they are going "slow". Do some shopping, get on the highway, turn the headlights on, kinda dim inside...

Pull in a friends house, grab a meter and check batt voltage while running...9v. Charged the battery, drove home, batt voltage down to 11v.

Figured it was the alternator. Took it off, had it tested at both AAP and Autozone. Tested good at both places. Not satisfied and knowing I had checked the power/ground circuits already, I bought a new alternator, got the troubleshooting sheet in the box and did the checks. Voltage at both S and L terminals, however the battery light doesn't come on with the key on, strange.

Out of ideas and not wanting to tear the gauge cluster apart, I put the new alternator on. Voila! Key on the battery light is on. Start her up, 14.2-.3 volts while running.

Is the alternator tester at both APP and AZ flawed? Or is this some freak mishap of circuitry inside the alternator?

 

[Jim]

My guess would be the brushes were about shot and when you removed the alternator you caused the brushes to move a bit allowing it work again. Not very likely that two shops had bad testers.
I have found that most alternators are good for about 150,000 miles.

 

[tunabreath]

I just hooked the old alternator up and with the key on the battery light is now on? Maybe I missed it before and it was on before but I didn't see it because it is hidden in the bottom. Im confused.

 

[tackleberry625]

does the alternator make a humming type sound as it turns?

 

[mechtech2]

It could be that the contacts were faulty.
Cleaning both ends of all you power and ground leads is smart and easy to do.
Also, internal voltage regulators [in the alt.] are solid state, and can come and go as they please.

 

[tunabreath]

I just reinstalled the old alternator.

13.6-13.8v while running. A little low, but it's an old alternator.

This is confusing me. I have the new alternator in the backseat with tools to swap it out. But for now, I am going to run the old one and see what happens.

 

[jnyost]

I would leave the new one in. One simple way to test your alternator without removal is to unhook your battery while your car is running. Your alternator should put out enough to power your engine.

Jared

 

[oilyriser]

I like how easy it is to do alt swap on subarus.

 

[kc8adu]

Originally Posted By: jnyost
I would leave the new one in. One simple way to test your alternator without removal is to unhook your battery while your car is running. Your alternator should put out enough to power your engine.

Jared

this is something to NEVER do on a modern car!
the regulator may not work right without the battery and may overshoot badly.
bye bye electronic$!

 

[dwendt44]

If you have the old alt. on try this:
Turn everything on. headlights(high beam), radio on, rear defrost, A/C and fan on high, hazard lights on, dome light on, lighter pushed in, glove box open.
Check voltage at battery while idling. if less than 12.5, alternator is shot.

 

[artificialist]

That, and the voltage spike can also wreck the voltage regulator on the alternator.

 

[kgb007stb]

Originally Posted By: kc8adu
Originally Posted By: jnyost
I would leave the new one in. One simple way to test your alternator without removal is to unhook your battery while your car is running. Your alternator should put out enough to power your engine.

Jared

this is something to NEVER do on a modern car!
the regulator may not work right without the battery and may overshoot badly.
bye bye electronic$!


Strong 1+, even in older vehicles that have no electronics, the diodes become overloaded with excess voltage and fry or semi fry resulting in immediate or probable down the line alternator failure. Either way, that would be one expensive test.

 

[tunabreath]

Still running with the old one on, checking charging voltage everytime I arrive at my destination. We'll see if I have any more problems.

 

[mechtech2]

Don't disconnect the battery on a running car.
We are not in the 1950s.
With a full load of accessories, your idle voltage may be very low. 12.5V is not a deal killer in that instance.
With a full load, see if it gets u p to 14V or so when you rev it to 1,500 - 2,000.
But that old alternator gave you fair warning - keep an eye on it.

 

[BuzzCut]

I would load bank your charging system There is a tester to put a load on it and measure the current. you can use the electrical accessories and a voltmeter but isn't as accurate or put enough of a real load on it to tell you much.

 

[eljefino]

You need a working battery warning light to energize the field current in your alt.

If that bulb, say burns out, the alt will not work.

If your car has a voltmeter instead, forget everything I say... but know the field circuit is energized somehow... good place for a wiring diagram.

I just brought home a ford contour real cheap with a blown fuse for all the idiot lights... this kept it from charging.

 

[tunabreath]

The battery light is in working order, so I know that is not the problem.

Also voltage drop tested all connections (batt positive to alt pos, alt case to neg post, chassis grounds). All were well within spec.

I'll keep you guys posted.

I'm thinking this is some sort of solid state circuitry problem in the regulator that will come and go as it pleases.

 

[porcupine73]

Hi. Sorry for the late reply. Soobs of that era had a recall for the alternator failing at high rpms. If the recall was never performed, it might still be open and you could get it replaced free at the dealer.

 

[deepsquat]

it s the regulator...just replace the alternator before you get stranded

 

[03cvpi]

I would be wiiling to bet the techs!! at both of those auto stores missed something. I had to work on a friends olds station wagon that had a charging problem. He had taken the alternator off twice to have it tested. They both said it was good. He didn't want to throw 270.00 at the car to replace the alternator. I tested the unit in car and output was at 13.6 volts, which is low when full fielded. I took the unit off and went to Autozone and they said it was good at 15.2 volts output. That was the tip, Yes it was good, but the output was way too high without resistence. On test it should fall between 13.9 to 14.5 volts max output and at or near amp rating. I had Van replace the alternator and the charging problem went away. The machines at the autoparts stores work well for testing, but usually the testor doesn't know what he is doing as in both cases that Van took the alternator in. The same guy tested it when I brought it in and he called it good. I had the same guy test the new unit before we left the store and it hit 14.4 volts, the tech!! actually commented that it was low output and it may be defective. I told him we'd try it anyway. That was 2 years and 30k miles ago.