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alex673
08-01-2013, 10:18 PM
Hi guys
I have a '95 XJ Classic/Limited with 4.0HO. Over the past week, I have noticed the battery is dead flat after being left overnight.
I first thought it was an electrical drain somewhere, but couldn't find it. Now I think I have found the culprit...
I put my multimeter on the back of the alternator, and with the keys off, it was reading 13v... I was under the impression that voltage was only available at the alternator while the car was running...
Can someone clear this up for me please??? Do I need a new alternator???
Thanks in advance.

Alex

prerunner1982
08-01-2013, 10:54 PM
Was the battery still connected to the alternator when you tested the voltage at the back of the alternator? If it was you were getting the voltage reading for the battery. The alternator will not produce voltage unless it is running. If you can jump start the vehicle and drive it, then the alternator is likely not the culprit. How old is the battery? I would suspect there is a bad cell in the battery.

I had a battery die over night for awhile, and then it would be find for awhile, then it would die overnight again for awhile. Eventually it bit the dust.

alex673
08-01-2013, 10:58 PM
I think it is all pointing to the battery. Thanks very much for your assistance!

xj4life2
08-01-2013, 11:37 PM
quick easy test for that is with the rig running remove the neg cable from the Batt. If the Jeep dies the alt is dead , if it continues to run the Batt is done or you have a bad connection somewhere.

NW99XJ
08-02-2013, 08:43 AM
quick easy test for that is with the rig running remove the neg cable from the Batt. If the Jeep dies the alt is dead , if it continues to run the Batt is done or you have a bad connection somewhere.
This procedure is correct except for one thing....dont remove the negative....that is the vehicle ground (-)....The alternator puts out a positive charge, so you'll want to remove the POSITIVE (+) battery cable....
This will isolate the battery from the charging system. Now even if the alternator is putting out less than the 13-14 volts that it should the jeep will still run....NOW would be the time that you'll want to test the system with your multi-meter. One lead to ground and the other lead to the disconnected battery cable. If you're seeing anything less that 13volts, the alternator is bad.
Your other option? Remove the alternator and take it one of your local parts stores, many of them will do free onsite testing.

ALSO.... one thing to consider looking at..... pop off the vent caps on the battery, and look down into the cells, they should be full of water...if not, top them off would good clean water, (bottled water will do, just dont use hose or tap water)...they shouldn't be full to the brim....just to the bottom of the "lid" of the battery.
Also check all your cables and their ends for signs of corrosion. If they are stiff, brittle, or green/crusty.....its time to upgrade.

nickyg
08-02-2013, 09:08 AM
Check out this video on how to perform a parasitic draw test.
http://www.youtube.com/watch?v=KF1gijj03_0

nickyg
08-02-2013, 09:22 AM
OPPS! I just read your post again, and just saw that you looked for a drain on your battery. Sorry, it's still early here..

alex673
08-03-2013, 08:33 PM
Thanks for your assistance, guys. Turns out it was the battery. Funny thing is I replaced it with a slightly more powerful one, and it works fine. Now I also fully charged the old battery yesterday, and this morning put a volt meter on it, and got 13.8v!
Enough voltage, but won't start the xj!!! Weird, huh?

Mudderoy
08-03-2013, 09:26 PM
Thanks for your assistance, guys. Turns out it was the battery. Funny thing is I replaced it with a slightly more powerful one, and it works fine. Now I also fully charged the old battery yesterday, and this morning put a volt meter on it, and got 13.8v!
Enough voltage, but won't start the xj!!! Weird, huh?

Electric has two important parts. Voltage and current. Voltage is the force and current is the capacity. Think of it like this. You have a small syringe full of water. You can press the water out of the syringe with a great force, but the water is gone very quickly.

Now think of a 5 gallon tank full of water. If you are able to push the water out at the same force as you did the syringe, you would have the same pressure coming out, but it would go for a much longer time before the 5 gallon tank was empty.

So you battery may have had the right force (13.8 vdc) but it probably didn't have the capacity of a fully functional battery.

NW99XJ
08-03-2013, 09:41 PM
Good Analogy!!!!