Mechanics

BATTERY WONT CHARGE

1992 Cadillac Deville • V8 FWD Automatic • 75,000 miles

I have a '92 Cadillac Deville. I got a new battery in January. One day I tried to start it and it wouldnt turn over I let it sit and it started up. I took it to two mechanics but they couldnt find an issue. It ran great until it happened again this november, I figured it was the starter. Today it seemed like the battery was dead so we tried to jump it. The first time the lights came on. Gave it about half an hour and no lights. I reconnected the cables and it sparked on the negative and pulled down on the other car. Let it sit and again nothing. Is this the alternator or what?
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Bgirl107
December 1, 2010.




"Let it sit and again nothing."

What does "nothing" mean? Everything is dead on your car? Everything works normally with no problem?

When you jump-started your car, were the jumper cables connected positive to positive and negative to negative? It's normal for the good car to load the engine down a little and its head lights will dim a little as it works to charge your dead battery, but it shouldn't stall the engine.

If everything was still dead on your car while the jumper cables were connected, there was probably a bad connection on one of them. GM side post battery terminals are REAL hard to get a good connection through. Also, GM went from the second best generator to the world's worst pile starting with the 1987 model year. There's no way to sugar-coat it, it's a very poor design and causes a lot of trouble. It is common to need four to six replacement generators in the life of the car. One way to prevent repeat failures is to replace the perfectly good battery at the same time. The old battery will work fine in older cars, but as they age, they lose their ability to absorb voltage spikes produced by these generators.

You can do the first test yourself. When the engine is running, use an inexpensive digital voltmeter to measure battery voltage. It must be between 13.75 and 14.75 volts. That applies to any car, any brand. In addition, due to their design, GM generators develop a lot of voltage spikes that interfere with the signals going to all of the complicated, unreliable computers on the car. Those spikes have been known to cause engine running problems. To test for spikes, you will have to visit a mechanic with specialized equipment, but that is not the problem with your car now.

If you measure battery voltage with the engine not running, you should find very near 12.6 volts if it is fully charged. If you do and everything on the car is still dead, suspect a bad connection on one of the cables. If you find closer to 12.0 volts, the battery is good but discharged. That is a sign of potential generator trouble. The dome and head lights will work but might be dim. If you should find less than 11 volts, that suggests a shorted cell in the battery. That isn't likely in your case since it's less than a year old.

Caradiodoc

Caradiodoc
Dec 1, 2010.
Thank you for taking the time to answer. When I say nothing I mean the lights wont come on. I know that I had the negative to negative and positive to positive and the connections were good. It did load the other engine down and it made the lights come on the first time but I tried to start it and it totally killed it again. Do you think there is anything besides the battery that could cause this?

Tiny
Bgirl107
Dec 1, 2010.
Measure the battery voltage while a helper tries to start the engine. If it stays up over, ... Oh, ... 11 volts or so, move the voltmeter probes, one at a time, to the next place down the line. Unfortunately with GM's side post batteries you can't get to the battery cable connection, but you should be able to find where the small black negative wire attaches to the body. Move one meter probe to that point and measure again. There also may be a red positive wire going to the under-hood fuse box. If you have that, check the connection to see if the nut is loose. What you're looking for is the point at which the voltage drops a lot or disappears completely. That will be the point of the bad connection.

Bad connections usually don't show up unless you are trying to pass current through them. That's the reason for taking the readings while a helper tries to crank the engine. You might have the same luck by turning on the head lights. Together they will draw about 15 amps with all of the tail lights turned on at the same time. That should be enough current to make finding the bad connection possible.

Caradiodoc
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Caradiodoc
Dec 1, 2010.

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