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Old 02-16-2010, 11:15 AM   #1 (permalink)
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Wierd electrical issue...any ideas?

I posted this here since I imagine there are some decent mechanics here and this gets the most traffic. I use this vehicle as a company delivery vehicle. It does have 468K miles on it.

99 XJ 2WD

I had a symptom where the plug in the back of the alternator was jacked up and it caused the battery to die and the jeep to idle sporatically. The symptoms would start and would be noticed by the volt guage moving around erratically. I took it in they determined that the spades on the back of the alternator was the issue so we replaced the alternator. This seemed to fix the issue.

A few weeks later, guages became erratic again, it sputtered and we eventually could not keep it running. I check voltage on the battery and it showed 12v. However, when you would turn the key it would spark at the positive cable connect to the battery, and click. I jumped it off and it started right up but you had to keep pressure on the gas or it would die. The Alt was putting out 14v per my meter. Came back the next day, jumped it off and it ran ok and the voltmeter showed 14v. Drove it about 12 miles to my house so I could work on it. Halfway there, the voltage dropped to 9v, it sputtered but we made it.

I removed the positive cables and replaced the battery clamp and cleaned up the wires. Battery showed 9v. I charged the battery. It showed 12v but it would not crank. The battery must be toast. I replaced the battery and it fired up, had correct voltage sitting 12v and charging 14v. It ran for about 12 hours and the driver got in it at a stop and it would not crank. Voltmeter was erratic. Jumped it off and got it back to the office. It would not run unless kept pressure on the gas pedal. The voltmeter then was pegged at 19v. Cut it off and it would not crank under its own power.

Jumped it and took it back to the shop. They fiddled with it but called and said the battery was toast and they need to replace the battery. Of course they did, everything was fine and they called me to come get it. I know it is not fixed and will happen again. I cannot send my driver out in it until I figure out what the cause is. Any ideas?

I am not an amatuer with vehicles but this has me stumped. It seems there has to be a wiring issue. Something has killed two batteries. When there are no symptoms I am getting the proper voltage from the alt 14v. Once the issues start; erratic guages, bad idle I am still showing correct voltage from Alt but it will not crank under its own power and the battery has been killed. I have not caught the alternator putting out more or less than 14v with my meter?????

Alternator new and putting out 14v
Belts tight
Cables clean
Two batteries killed
Voltmeter on vehicle erratic with other guages when the symptoms start.
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Old 02-16-2010, 11:34 AM   #2 (permalink)
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sounds like bad grounds. You said you installed a new + cable but what about the - cable.
buy a new one and run it directly to the engine block. You will aso need a good ground to the body and frame as well.

Run a voltage drop test. Put your volt meter between the engine block and the - post on the battery. crank the engine, if your meter shows more then a 1 volt, you got problems. Poor cables cause most of the charging and starting problems. Once the engine is running, do the same test from the -battery post to both the body and frame.
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Old 02-17-2010, 07:26 AM   #3 (permalink)
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Thanks, that is the next logical step. I did replace all of the grounds last night. Cable from - to body/frame, cable from - to block and cable from block to body/frame. I did run the test from each cable location and got anywhere from 30mV to 6.1mV. After reading your post again, I will test again but somewhere beside the actual cable mount locations.

Having a brand new Alt and the previous Alt only having an issue with the "plug" I am ruling it out, unless there is something crazy going on with the voltage regulator inside. Since the "plug" was the original issue I may try to replace it using spade connectors. Perhaps the two wires in the plug are crossing or something.

After replacing the cables, it runs fine and the voltages are where they are suppose to be. I guess I can only run it around and wait for the symptoms again, of course it could cost me another battery if I cannot identify the issue.
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Old 02-17-2010, 11:50 AM   #4 (permalink)
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Look in to your PCM as thats where your charging system is controled.
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Old 02-17-2010, 02:04 PM   #5 (permalink)
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Interesting...would the PCM be able to fry the batteries? If it is an intermittent problem are there any suggestions on how to tract the issue down or is it a "replace and hope it fixes it" deal?
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Old 02-17-2010, 04:35 PM   #6 (permalink)
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Find a shop(or your self) that can moniter your charging system and load it up with lights ,A/C, etc. and watch to see if it is being regulated,or just looseing(sp) voltage
And yes it can over charge your battery and fry it.
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