Okay. I I've been recently having some problems with my car's battery dying. It seems that it'll just die off. I replaced the battery a few months ago. I replaced the battery terminals also. I figured I had to check the alternator next. I pulled out my alternator/battery tester and before I started the car the battery was showing up as "very strong" on the tester meter. I turned on the car and it started right up. I checked the meter again and it gave a "very low (13 volts or less)" output on the meter. However, when I turned off the A/C, the meter shot up to a "very strong (14 volts or higher)" output. I turned the A/C on again and the meter fell back to "very low." It's been hot recently down here so I've been running the A/C most of the time except at night for the first time in weeks. Shouldn't the alternator pump out nearly the same amount of juice with the A/C on as with the A/C off? I would've assumed that worst case the car running with the A/C on would've dropped the meter down to "Strong/normal" from "very strong" as opposed to "very low" output. Am I right here guys?

Sounds like a bad voltage regulator in the alternator .

So, replace the alternator then right?

yep your next step is replacing the alternator

Are you running reduction pulleys?

Nope! Just the stock stuff. I thought reduced weight pulleys were a good thing?

"Under drive pulley systems increase engine horsepower by reducing the amount of power required to drive external accessories. For example, the alternator, power steering, water pump and air conditioner all rob horsepower from the engine. By replacing factory-sized crank and accessory drive pulleys with a resized pulley, the accessories are slowed, resulting in more horsepower available to drive the rear wheels."

If I had to replace the alternator I was going to take advantage of the timing and go with underdrive pulleys.

Underdrive pulleys will not help the a/c or alt. perform well at an idle.

True if you just normal drive your car you don't need underdrive pulleys for your car now if you were running a alt. only on a street strip car that might be something to get .

I run a high amp alternator with a overdrive pulley, because I want my amps low on the rpm. Underdrive pulleys are usually not worth the time and $$$ compared to other performance options unless you have a honda.

So I shouldn't even waste my time and money then?

Pulleys are kind of like octane booster, sounds like a good thing but don't help much!

I know, I just got around to doing this but I finally took the alternator out and went over to Autozone and had them test it with their fancy-schmancy alternator tester.

Their tester passed the alternator in every phase. I told her my alternator tester (which is a cheap one from Harbor Freight) tested it fine with just the engine running but with all electronics on it was showing a low output. She said that their tester tests everything including the voltage regulator. She said she'll run it again just to be on the safe side.

On the second run, it still passed all three of their alternator tests. I'm confused now. The battery is new. The battery terminals are new. The alternator is working properly according to Autozone's tester, so wtf?

Not sure what your tester looks like but could you possibly hook it up to the alternator? Negative on the casing and positive on the big red wire. If it shows better results, I would suspect a problem in battery cables or other wiring.

Lou

also try checking for parasitic draw

Not the cables. Cables are new. As I stated I already replaced them along with the battery as well. I'm going to try the test you suggested also just for kicks and see what it says. My tester is like a simple light tester that has six lights on it. Three lights for battery and three lights for alternator. It goes from low to average to good.

The only time it drops to low is whenever I turn on all the electronics. If it's just the engine running it displays good.

How?

Ok, well we're back here. Reason being is this.

I've had the alternator tested at Autozone twice and Advance Auto once. Both places testers say it's good. I noticed that when I'm idling, even though it's not idling rough unless I'm running the A/C, the needle on the voltage jumps up and down. It sits at slightly over 13 volts and then it slips down to about 12 and slowly creeps back up to 13. It'll repeat this until the light turns green and you step on the gas and go forward.

Any thoughts? Voltage regulator maybe?

This article might be an interesting read for you.

http://www.autospeed.com.au/cms/A_111306/article.html

my car does the same exact thing! if it idles and i put the a/c on it will get low to maybe 13 volts, then when i put the car in gear it idles at 500 rpm and has 10 volts and wants to stall out... so i just need a new alternater?? also sometimes when i start it up the belt will squeal for 10 seconds or less, i know its the alternator belt because my batt voltaget is low, and sometimes when i drive the car with the high beams on it will be fine then when i let off the gas, down goes the volts, down goes my rpms to the point where it just barely stays running and the belt squeals untill it press on the gas again..... please tell me what y'all think, do you think it could just be a bad alternator maybe a bad bearing thats holding it up?

i had the same problem ,,got caught driving in the rain ,,turned on the fan and lights and wipers,,,the idle started to go down and almost die ...i noticed that if i drive with no options on except maybe the radio it runs great ..but with a load it wants to die ,,the alternator pumps 14.6 volts at idle but with a load it goes down to 10-11 volts ,,,i verified this with my multimeter.,,but i also brought the alt to a place where it shall remain nameless and they told it's fine ,,,i bought a new one -100 amp and for about $75 ...it stopped doing the problem and runs fine with or without load...these people working at these places are mostly unexperienced kids ..no offense ,,but i woudn't trust the alternator tests they do ...

Yea, I hate the punk kids that work at them places like pepboys and such, everytime i go in to get a part they think its a joke, and or they don't know what im talking about, im young myself and i know more than some of them do, But anyways, you said you got a higher output alternator?? and it fixed the problem? do you know how many amps the stock one is??? and do you know if it matters that i have a ribbed v-belt for my alternator, I didn't know if this is the cause of the squealing,(hell it may even be the cause of the low voltage..) but it did it before i changed the belt, but does it matter if its a ribbed v belt for my alternator, the one before it was not ribbed it was just flat to fit in the pullley. thanks

well , i didn't want to insult anyone , but your right !...i got an alternator which is 100amp..i don't have a/c and this alternator would be appropriate for a car equipped with a/c..but the place where i bought it made it at the same price,,i think a regular alternator would be 65-75 amps ..but not sure...mine has the regular v-belt.
it is great now on idle with any option on like the fan or lights or fog lights -wipers etc...it keeps the charge.

They make several alternators for our cars. Is there anyway to tell them apart by looking at them? Any of them fit from a fourthgen?

my alternator is the older style gm type , it is bigger and has the regular one v/belt pulley ..i think the 4th gen ones are smaller and have a bigger serpentine belt pulley ...you can tell them appart...i don't think the 4th gen alternators would be a direct fit on the older camaro/firebirds like mine...but verify,not sure

No, you'd have to at least change out the pulleys. I was just wondering if anyone has done it.

Is there anyway to tell the alternators apart amperage wise just by looking at them in thirdgens?