I had my car (92 LT1) off the road for a few months for repairs. I changed the opti to an msd, new water pump, wires. When I got her laa done I found the battery was dead. i had disconnected it when the work began in december. I charged it up and she started the first time. Back was that nice loping sound I had missed. Ahhh i wnet. Drove her around town town and the voltage was low. It was varying from 11.2 to 12.4. LAst night I made it to the end of the block and the vlatge dropped and the car quit. I jumped it and with the lights off coasted into the drive way as it had died once again.
With all of the electronic controls I am assuming that the car wont run with a battery as the old V8 non electronic engines would. As the battery was dead does it make sense that its is the problem and will no longer hold a charge to supply the rest of the system or is it it most likely that by fluke the alternator is dead?

 

Sounds like a dead battery to me. The battery was allowed to deep discharge and left in that state for a few months. If your car was charging properly before it sat that also would lead me to suspect the battery. I always use a battery tender when my cars or batteries are not in use. That keeps them stimulated and extends their life. I'd put a new battery in.

 

If it was only registering 11.2-12.4 while driving, it is not charging.

The battery may or may not be bad, but as long as charging voltage is less than 13.2 the alternator is not charging sufficiently and your car was "running" off of the battery only. The battery won't "run" the car any longer than it's reserve voltage will allow it to, which is no different than an OLDER car. In a nutshell, the car actually "runs" off of the alternator. If the alternator is charging, you can actually remove the battery if you wanted to, since it does nothing but START the car. If the alternator isn't charging, and yours isn't, than the car runs on battery only and can only run until the battery is dead.

Is it possible you pulled or broke a wire while doing the repairs you did?
I'd double check battery and alternator connections, then if all looks good, take the battery and alternator to a garage or parts store that has the proper bench testing equipment and verify the condition of both. Obviously, the battery would need to be charged beforehand, in order to load test it. FWIW, 12.6 volts is a fully charged battery, and my car (even with underdrive crank pulley) charges 14.2 volts at idle.

FWIW, a DEAD BATTERY will NOT make a car DIE while RUNNING...a bad alternator WILL...

 

A dead battery can fail in a way that will indeed stop the car while running. When the voltage drops below what the comp needs or too low for the ignition to make spark it will die. Your alternator could be just fine. It is not good for them to charge up fully discharged batteries though. A short anywhere, including inside the battery can easily overwhelm the output of an alternator.

Pull the battery out and charge it on a trickle charger. It should read over 12 volts when it's ready. Take it to your favorite parts store and let them load test it.

When you've replaced the battery, the alternator should output 14+ volts at idle.

 

http://forums.corvetteforum.com/show....php?t=1614075



I had a NEW alternator that tested fine in the car and under load. Since the car continued to die I exchanged it for another new one and it's been fine ever since.

 

You have a defective alternator and your battery symbol light on the dash should have been lit. The alternator attempts to maintain 14.7 volts output (14.3 on your dash voltmeter) when the alternator is cold and the output voltage drops to 13.3 volts (dash reading) when the alternator gets to its operating temperature. Furthermore, you should never let a lead acid battery sit for long periods (4+wks) doing nothing because even disconnected they self discharge up to 1% each day and lead sulphate collects on the plates. A fully sulphated battery is a door stop. You definetely have reduced the amp hour capacity of your battery. Each time you deep discharge a car battery, it loses some amphour capacity.
Buy a battery tender and keep your batteries fully charged when you aren't using them for a normal battery life.
You can tell the state of charge in your battery by measuring its no load battery terminal voltage. 12.9 volts and higher, fully charged. 12.0 volts and lower, discharged and linear in between. Your engine quit because the battery voltage got too low to allow spark and other circuits to work properly. This doesn't happen when the alternator is working properly. Measure the resistance between the alternator output and the positive battery terminal, it should be the same as touching the ohmeter probes together. Anything higher and you likely have a damaged or blown fusible link in the alternator ouput wire. Replace it if the ohmeter tells you its toast.

 

I had that exact thing happen and it was simply a SLIGHTLY loose positive connection at the battery. However best to check both the battery (first) and alternator (second) just to be sure.

 

Change your battery or the low battery will kill your alternator.

 

Note, that after discussing a similar situation, I was informed to never run the car without the battery, you could fry one or more of the computers, same for jump starting.

A dead battery can cause the car to not run, but so can a bad alternator, they usually work hand in hand.

 

Mr. Mojo, you were told wrong! I'm an EE and you can safely jump start your car AND you can safely run your car only on the alternator!

 

I was told that the old fashioned way of removing the battery to see if the car stalls will damage the diode bridge in the alternator.

 

You too were told wrong! The diode bridge doesn't have any more load on it with or without the battery, in fact the alternator has less of a load on it without the battery because you eliminate the battery charging current.

 

What I was told was that when the car is running, alternator charging, that if you remove the battery to test to see if the car stalls, that could/would damage the diode bridge. Are you saying that is NOT correct? (sorry for all the comma's).

 

Removing the battery makes for a sudden drop in current load on the alternator. The only possible way for any damage to the rectifiers is a voltage spike with enough energy to not only exceed the PIV (peak inverse voltage) rating of the diodes, but enough energy to damage one or more rectifiers and that isn't possible. The rectifiers are designed to withstand the normal transients that occur in auto electrical systems. The voltage spike comes from the inductance in the battery cables (very very small inductance) and the high rate of change of current (usually small with a charged battery). The majority of any voltage spike when disconnecting the battery will be dissapated in the small spark that occurs when one battery cable disconnects, not in the alternator rectifiers.

 

Thanks for the Info! Good to know.