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1991 Ls 400 - Alternator Problem?


1991LS400
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Hey guys, here's yet another technical question...

The other day, what I THOUGHT to be a starter problem ends up being either a battery and/or an alternator problem. A friend of mine charged up my battery with some cables and after about a minute or two my car turned on with NO problem. I drove it around for a few minutes and then parked it again. The next day, I came out to turn on my car and it was dead again. Same repeated clicking when I turn the key all the way. I can tell the interior lights were dimmer than the day before when my friend charged my battery up.

My battery is only 2-3 years old, at the most. I am NOT running anything in my car that would be taking excessive amounts of juice from my battery. I'm not sure how old my alternator is, it's the same alternator that was in the car back when I bought it in 2003-2004. For all I know, the alternator COULD be as old as the car itself (about 17 years).

For you experts, do the signs seem to be saying it's an alternator problem or a battery problem?

If it's the alternator, would anyone here happen to have any type of manuals or instructions on the easiest way to go about getting to and removing the alternator? I don't think it's as hard as a starter, but I heard you have to go from under the car to get the alternator out, is this 100% the only way?

Thanks in advance for any help! =)

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There are several things you could check to try and diagnose the problem.

First, to determine the health of the battery, you need to check the charge state (specific gravity) of each of the individual cells of the battery (assuming it is not a sealed battery). The thing to look for is differences between the cells. If you have one or more cells that have significantly lower charge states than the others, the battery is dying and should be replaced. Auto parts places have the testers needed to do this. Don't get one of the cheap testers that only show charge state. Get one that actually shows the specific gravity of the battery acid. These are larger and more accurate.

You could also do a load test on the battery. This takes a tester that you hook up to the battery. Flip a switch, and the tester puts a load on the battery. A display will indicate if the battery is bad. Most auto parts places can do this for you, normally at no charge. Load testers are available at places like Harbor Freight for around $25.00.

If you determine that the battery is okay, check the output of the alternator. Using a multimeter, check the battery voltage without the engine running and then again with the car running. The voltage without the engine running should be in the area of 12.6-12.8 volts for a charged battery. When you crank the car, the voltage should go to somewhere in the area of 13.7-14.0 volts. If the voltage does not go up this high, you likely have an alternator problem (or some kind of connection problem).

Given the well-known propensity of the LS models to have PS fluid dripping on the alternator, a look at the alternator might be in order, too.

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There are several things you could check to try and diagnose the problem.

First, to determine the health of the battery, you need to check the charge state (specific gravity) of each of the individual cells of the battery (assuming it is not a sealed battery). The thing to look for is differences between the cells. If you have one or more cells that have significantly lower charge states than the others, the battery is dying and should be replaced. Auto parts places have the testers needed to do this. Don't get one of the cheap testers that only show charge state. Get one that actually shows the specific gravity of the battery acid. These are larger and more accurate.

You could also do a load test on the battery. This takes a tester that you hook up to the battery. Flip a switch, and the tester puts a load on the battery. A display will indicate if the battery is bad. Most auto parts places can do this for you, normally at no charge. Load testers are available at places like Harbor Freight for around $25.00.

If you determine that the battery is okay, check the output of the alternator. Using a multimeter, check the battery voltage without the engine running and then again with the car running. The voltage without the engine running should be in the area of 12.6-12.8 volts for a charged battery. When you crank the car, the voltage should go to somewhere in the area of 13.7-14.0 volts. If the voltage does not go up this high, you likely have an alternator problem (or some kind of connection problem).

Given the well-known propensity of the LS models to have PS fluid dripping on the alternator, a look at the alternator might be in order, too.

That's all fine and dandy. But please, does anyone have any manuals showing how to get to and remove the alternator? I just want assumptions on what the case may be. If the battery is dead, I'll buy a new one. If the alternator is dead, I'll buy a new one. But I'd rather only have to change one thing at a time.

And obviously, between a battery and an alternator, we all know it will take more time to switch out an alternator.

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Calm down. I've had my '94Ls 5 years, and am on my third battery. You're messing around with a possible cheap solution. Install a new battery-gee, maybe 80 bucks and 10 minutes max labor. Then see what happens. If it's the alternator or whatever, I'm wrong, and you'll have a big cost-but at least you'll have a new battery. Bet it's the battery-the clicking is the key.

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Before you start buying replacements, make sure the part is defective. Cheapest first........as cardona says, make sure the battery terminals and connectors are clean and tight. Next check the tension on your serpentine belt. Then, check the ground on your alternator. After load testing the battery and alt, you're ready to buy what you need.

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It is probably your alternator but start with the cheap, routine stuff, like checking the battery and terminals.

Places like Sears will check your alternator for you.

A sure sign of alternator problems are idiot lights being triggered when after checking, there is no fault.

I changed my alternator with a rebuilt and the repair is very routine. A helper comes in handy to start the attaching bolts as you juggle this heavy item into position from below.

glenmore

1990 LS400

1991 300CE

2000 C280

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