Sorry, this is a long post. If you want to skip i have added cliffnotes before my questions, or you can read the whole story. Thanks in advance.

My volt gage has always been around ~12v, well last week i was driving and i noticed my gage in the top of the red at about 10v. I was about 20 miles from home and kept going. By the time i got home it was only at 8-9v (just above the bottom mark). The car ran fine, no hesitations or anything. It was daylight so i didn't have any lights on and i shut my radio off once i noticed the gage in the red.

Well i got home, car still running fine, gage at 8-9v. I got out and checked the battery and alt with a multimeter. The terminals across the battery were only showing between 10 and 11 volts (Can't remember exactly) and the altenator was at 13.5 volts (touched the terminal on the back and the ground on the wheelwell.
I shut the car off and it wouldn't restart. It cranked slowly for a second then stopped. Just like a dead battery would. I got out a battery charger and let it charge for about 20 minutes, still acted like a dead battery, used the 12v start option on the charger, didn't help.
*The battery is only 6 weeks old, die hard gold, and the alternator is a new ac delco as off last fall*
I took the charger off the battery, waited 30 mins, car started, still low voltage. I shut it off and it wouldn't restart, dead battery symptom again. No clicking as if a bad starter either. Tried a few more times that night, random starting but mostly no start and always low voltage. Checked voltage of battery alone and it was ~12v even. Thinking maybe a dead cell.
Pulled the battery, charged it and put it in an 86 firebird. Same symptom, wouldn't start, slow crank and stop. ( I wanted to try the battery from the firebird in the camaro, but it was dead because i never drive the firebird)

Went back to sears, they gave me new battery. Went home, put the battery in and it fired up. 13 volts, great. But as the car warmed up it dropped back down to 11-12, but never in the red. I cleaned up the grounds on the frame and engine. Last fall i did the same to the positive junction block and ground block on the inside of the fender.
This didn't make any noticible difference with the gage.
BTW the readings while engine running across the battery terminals are 13.1V and the alternator post to ground is ~14.3V. The battery is ~12.6 volts when shut off.

*CLIFFNOTES:
Driving, volt gage ~8-9 volts, running fine. Batt ~ 10-11V, alt ~13.5v. Shut off, wont restart, acts like a dead battery. Recharge battery, still no start. 6 week old battery, ac delco alt. last fall. Get new battery, starts fine. Voltage not in red but still only 11-12volts.

My questions are: Is it normal for the gage to be at 13v on startup then drop to 11-12. I know the gage isn't the best to judge by, just gives me an idea.
And how can the gage be showing 8-9v and the car be running fine? Will a bad battery cause this, or is there another problem?
Could this have all been caused by a dead cell in the battery?

Thank you,
-Greg

 

it could be your running lights come on when you release the E-brake. my voltage moves when I have a turn signal on because it flashes off and on again... just a thought.

 

The alternator is connected directly to the battery on the positive side. The ground however has to rely on the frame of the alternator being grounded to the engine. The engine is grounded to the body and the battery is grounded to the body.

The only thing that could account for the drop in voltage from the battery to the alternator is a poor connection.

Since you checked and cleaned all the grounds, it would appear that the alternator does not have a good clean connection to the engine. Perhaps it's mounting bolts are loose or corroded???????

You can also check for high resistance with an ohm meter. Be sure to disconnect any wires from any voltage source that you wish to measure for continuity. You can check from the case of the alternator to the negative battery terminal.

 

Thank you for the responses.

Mortify: If you mean daytime running lights, I don't have them on the 94.

Speedy: Since the battery is hooked directly to the alternator on the positive side, the voltages should be close correct? The connections between the two are tight, however, I did touch the cable between the two and it was significantly warmer than the rest of the wires. I am thinking that the wiring might be corroded inside and causing a greater resistance which is why it is getting so warm. I have ordered some new thicker battery cables.

Are you saying to disconnect the positive battery terminal while checking ohms from the alternator case to negative terminal? To check the ohms across the positive wire to alternator, do i disconnect both battery and alternator?

i did drive the car some this weekend and my volt gage never dipped in the red, so maybe it was the battery. But i still don't understand how the volt gage could have been so low while the alternator was working fine and the car was running good?

Thank you,
-Greg

 

Take it to Sears and they will check it for free and tell you what it is. Sounds like the bat.

 

Thats what i did. I got it replaced for free and i haven't had the problem again but i am just trying to see if it could have been anything else. Allthough, the guy only checked it with a multimeter, I should have had him load test it. I didn't think of it at the time.

 

 

Quote:
i still don't understand how the volt gage could have been so low while the alternator was working fine and the car was running good?
************************************************** *************************

The motor was running off of the alternator but your volt gage reading
was off of your dying battery.



Checking your battery:

This is verbatim out of my Haynes manual.

"Using a voltmeter, check the battery voltage with the
engine off. It should be approximately 12 volts.

Start the engine and check the battery voltage again. It
should now be approximately 14 to 15 volts."

93Z,383,Vortech,NOS,h2o/methanol

 

I would check the voltage across the battery terminals. Sometimes those dash gauges malfunction or are not always terribly accurate either.

 

After reading your post I 'm thinking you should check your battery cables.
If you have 13.5 volts at the back of your alt.than you should have the same at the battery. The alt. is connected to the battery first than it goes on .
Just an ideal.

 

Okay, that is good to know. The gage was reading off the low battery while the car was running off the altenator. I just wasn't sure why it dropped so much. I only had my radio on, no lights. But over 30 minutes the radio could drain a weak battery.

2000GTP: I did check the voltage across the terminals at the time and it was 10.X volts. Now with the new battery i am getting 13.1 volts while running. And yea, the gage is usually lower than the battery.

Ayers: I did check my battery cables, they are all tight and clean. I have ordered some new cables. The voltage at the back of the altenator is 14.5 V.

-Greg

 

UPDATE:

Since the new battery, May 28th, the car had been fine ~150 miles.
Yesterday the gage seemed to slowly drop closer to the red. I got where i was going and shut it off for a couple of hours. It started up fine then the gage went in the red ~10 volts and stayed there. I drove through the parking lot and it stayed in the red. Pulled out on the street and ran the car up to 4000 rpm through 1st and 2nd and the gage jumped up to ~12.5 volts and stayed there all the way home.
I didn't have my multimeter with me to check under the hood. I shut it off and started it back up, no problem.
I am very confused. I am going to have the alternator tested.
Can the alternator work intermittently? I just don't understand why the volt gage went so low again and then came back and stayed.
I am also going to replace the belt tensioner and belt thinking maybe the belt is slipping and possibly the high rpm run got the alternator charging?
Any other ideas?

Thank you,
-Greg

 

Thats very possible. Did you ever check the line running from the alternator to the battery and saw what the voltage read?

 

Yes, I have checked it. Everytime i check across the positive cable bolt on the back of the alternator and the ground block on the fender i get ~14.4 volts. From the positive battery terminal to the ground block i was getting ~13.1 while running. This was before yesterday though, i didn't have a multimeter to check with when i got home. I will have to check again.

 

with it running, put the positive lead of the multimeter on the alternator stud, and the negative cable of the meter on the positive terminal of the battery, tell us the reading (ps, this is know as a voltage drop test)

same can be done on the ground side, put the leads on the alternator case and the neg batt terminal