Voltage Problems...

[Lockerz]

[Edit: I originally posted this in Electronics and Audio and then realized this is the better section. Sorry, i'm still getting used to everything here. ]

Whenever i'm at a stoplight the voltage meter drops to slightly below the halfway point because of the brake light. Then as I hold the brake, it kind of bounces between the full charge mark and the halfway point; occasionally dropping below the halfway mark making it feel like the car is going to stall.

I just got a new alternator and really don't want to blow it.
Also, I filled the battery with distilled water which solved the problem for a little while. I'm starting to think that it might be because I let the battery water get a little low in the first place which might have damaged the battery internally. (Oops.)

What do you guys think and is there anything else I don't know about that I should check?

[berettaboi]

likely your idle is surging a bit as well when your battery gauge is bouncing a bit... pretty typical of older GM's. start with an idle relearn, it's quick and easy, and also happens to be free.

pull the negative battery terminal off for about 5 mins, longer if you can find something useful to do with your time while waiting... then hook back up start the car and turn on everything that will load the alternator and ultimately the motor down to the lowest idle that it will learn to like. if that doesnt take care of the issue, then keep your eyes open on a few other topics going on, and also typical tuneup style stuff and carbon cleaning.

[scd88ga]

It doesn't sound like anything's wrong with the charging system to me. Electric motors make less voltage when they spin slower. I'm not sure why you had to add water to your battery? I'd get a new one anyway. :/

[Lockerz]

@scd88ga I know I thought it was crazy at first too but it is mentioned in the Chilton's manual. My battery is a maintenance battery and needs to have distilled water added to it every once in awhile to keep up the charge. There are also maintenance free batteries with built in hydrometers but I don't have one of those.

[Money pit Beretta]

That is wild. They don't even sell those batterys around here anymore.
So does the idle go up and down too?
Also what brand is this battey? Hope is not an Interstate. They work fine to a point and then they are junk. Once they start having problems then it's time to get rid of them.

[Lockerz]

@Money pit Beretta Well this is further to my embarrassment but where would I check the idle? Is that the RPM thingy on my dashboard?

The battery is a Duralast Gold.

[Lockerz]

@berettaboi I'll try that tonight...or possibly tomorrow morning, it's a busy day.

[ifixalot]

Note the position of the meter with key on and engine not running. With the engine running, anything above the noted position is charging.
As someone stated, when idling, the alternator is turning slower and will not put out as much. So a lower reading at idle as opposed to cruising is normal. Mine goes into discharge when the AC is on high at a stoplight. I usually apply a little foot to the gas if it's a long light.
I put a little mark on my meter to tell me when it's discharging.

[Money pit Beretta]

You have a GT so you should also have a tach(shows the RPM of the engine). The easy way to find it is to rev the engine(just a little) in park. The tach will be the biggest needle to move. Also if you look close it will say RPM x 1000 to the right.
Duralast? Isn't that a Ford battery? I think it's time to upgrade to a maintenance free battery anyway.
Starting to think you have a lose connection somewhere. You replaced the alt so we can rule out the regulator.

[Lockerz]

@Money pit Beretta @jskiguy I think I should upgrade the battery. I just had her stall on me. I drove a couple blocks and everything seemed okay, parked her at the store, started her back up and then she stalled. I don't know what else it could be really.

I'll check what the idle does too on the way to work now that I know what to look for.

Thanks very much. :B

[ifixalot]

If it started right back up, your battery is OK and not causing the problem.
Re-reading your post it sounds like the engine is going low in idle rpm and thus reducing the alternator voltage.
Your car won't stall due to low voltage unless voltage gets way down under 9 volts.
Your battery being a bit low on water won't hurt it unless the water was below the plates for a long time.
Your idle is surging for some reason causing voltage fluctuations. It's not the voltage causing idle problems.

[Money pit Beretta]

Keep posting what it's doing. The more info the better.
Like the idle goes up and down at spot lights and stalls sometimes. Idle drops very low when in gear(almost stalling) and stays there. Just about anything you can give will help.
I would bet money that the check engine light is not on all the time. Does it come on at all when in gear? Say after driving over 45mph?

[Lockerz]

Ok so when I drove to work yesterday the idle went like this:

In Park: 1
At a stoplight: 1/2
Driving: 1 - 1 1/2
Accelerating: 2

The voltage went down a few times but it didn't stall. When the voltage went down it didn't seem to affect the idle anymore than it did anything else on the dashboard.

@Money pit Beretta The check engine light hasn't come on at all yet but I just really want to figure out why the voltage is doing what it does before it gets worse.

@jskiguy I'm starting to think the plates might have fused. The alternator is brand new so I don't think it has anything to do with that. Otherwise, I don't know what else it might be.

[ifixalot]

I don't know what the numbers you refer to are. My guage has 8 volts at the lowest and 18 volts highest with three marks in between.
Normally, while driving it will be near the middle mark which is about 13 volts. It will drop down at a stoplight to below the first mark depending on
how much stuff I have turned on, (heater, AC, headlights etc.) Less stuff on, the needle will stay higher. It sounds normal to me since you said the alternator is new.
But, there is the heavy thick wire coming off the back of the alternator, if that is hitting metal and shorting, it can cause the engine to die and it will eventually burn through and disconnect. It may also damage the alternator by overloading it. Check that.

[berettaboi]

your normal idle should be around 700-800 rpms, your lights may dim (and battery level slightly lowers) will likely happen from 700-600 rpms if your idle surges a little bit. pretty normal for GM's of the era.

my 95 is usually just above the half way mark at idle... around 15 volts. should be anything around 14 volts when running at idle. with lights and other accessories running, you may drop down 0.5 to 1 volt or so.