Alternator diagnosis help (long)

Face · 08:15 AM

I've read most of the archived posts and still can't seem to find one specific to my problem! Battery died last week (89 3.2L Carrera) for no known reason, replaced it with a fresh DieHard. Initial assumption was that I had an old battery - easy fix. Not so fast...
Drive to work (short trip) two days later in the rain and the car doesn't even have enough V to turn the starter by lunchtime. I get a jump and head to Sears where they do the battery tester - it says BAD BATTERY - so we replace it (for free w/ 18 month warranty). I'm starting to think Voltage Regulator frying batteries at this point. I get the old Digital Voltmeter out and start my testing (the same day I have the second battery installed).
Battery reads 12.2V.
Reads 13.8V at idle, no accessories on.
Reads 13.9V at 2K with nothing on.
Reads 13.4V at 2K with brights, radio, and rear defroster on.

These all look pretty normal to me - maybe I really did have a bad lot of batteries. Well, this morning I go out to double check the readings - battery at 11.9 w/ engine off, idle at 13.7, looking good, then I see the voltage drop to 12.2, 11.8 while still at idle.
Oh boy, alternator is erratic. The weird thing is, when the alternator stops producing juice, the engine tone changes slightly. With the DV connected, I noticed while the engine made its usual whining/whirring sound, the readings were normal, this whining sound goes away and no charge coming from the alternator! The idle speed stays constant around 900, its just the sound that differs.
I'm at a loss here, fellas, help me out!
It cycled a bit between the two but spent more time at idle w/o this noise - therefore draining the battery slowly. Anyone have any ideas? Time to rebuild the alternator? I could buy a battery charger but that isn't really fixing anything!
BTW- The Idiot Light only lights up at the normal times. I.e. When the ignition is switched to on, then it stays lit while the starter engages, and then goes out when the engine gets to idle.

Put a chip in about a month ago (probably unrelated but I'll throw it out there), which I may switch today just to be sure.

Early S Man, John Walker, you guys know this stuff!?

Rot 911 · 08-30-2002, 08:55 AM

Todd I suspect a bad voltage regulator.

Face · 09:47 AM

Kurt,
I was under the assumption that I would see high numbers coming to the battery if the voltage regulator was bad. Like 16-18V, causing the battery to boil over due to overcharging. Can regulator problems also cause the alternator to charge intermittently? Thanks again.

Edit: Could the whine mean that is when it is producing current? It used to have this whine all the time I think, and now it's only occasionally.
The alternator light comes on only when I actually crank the car, not in the "on" position as it has before (with the oil light), then goes out when the motor starts. Arrgggh! So, I know the bulb works at least... points to a bad altenator I suppose.

Wil Ferch · 08-30-2002, 09:59 AM

Guys:
Look at the original post, and now chew on this:
- normal "full" charge of battery should be 12.6 volts.
- at 12.4 volts..you're at 3/4 charge
- at 12.2 volts, you're likely at 50% or less than full charge.
- battery is between 0 and 25% charge at high 11 volts.

Yep...the profile drops THAT fast !

This should be a hint of what's going on...

-- Wil Ferch

Face · 08-30-2002, 02:01 PM

bump... sorry, I need some help

john walker's workshop · 08-30-2002, 04:41 PM

sounds like the alt/reg unit is used up. charging 17 volts isn't the only reason they're replaced. the brushes on the reg, which is mounted on the rear of the alt, wear down, and in the process, wear deep grooves in the alternator's commutator, which is too thin to machine true again. then the brushes touch the comm sometimes, and sometimes not. if there's an auto electric rebuilder near you, they usually can glue on a new commutator, and rebuild the rest, often in the $100 range. i've had good luck with the PBR brand, which is a OEM rebuilder. better prices than bosch, or buying a new one. i assume the battery connections are clean and tight.

Face · 08-30-2002, 05:10 PM

Thanks John, yup the battery connections are clean and tightened down.

Face · 09:48 AM

Here's the latest alternator/regulator project update. I received the rebuilt unit from Alternator Express (w/ rebuilt voltage regulator) and installed it last weekend. Fire her up and see good numbers on the VM initially and then spikes up to 17-18V. Sh$t! The whole bright/dim light drill complete with seatbelt light is flashing before me. The idiot light flashes intermittently every minute or so.
Now I'm thinking, why did I go for the $158 alternator?! Anyway, after driving a bit with the VM hooked up I decide it has to be a bad Voltage Regulator. So, I order a fresh NEW one from Pelican, install is this morning and put everything back together.
Now she's running like a champ!

I also adjusted my throttle linkage to get full throttle (I had about 3/4" to the stop) and can notice a slight improvement there!
Anyway, just wanted to pass the word. "You buy cheapest part on the planet, you may get cheap part, grasshopper!" Not knocking the company, customer service was good and the alternator tests fine. We'll see what they say about the bad VR today.

Cheers,