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Old 07-07-2008, 11:09 AM   #1
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Can anyone confirm its the alternator

Hi

While the evil ones '97 TJ (thats the wifes if you hadn't guessed ) engine is cold everything is just fine but when the engine gets to temperature the check guages light illuminates and the voltage guage goes to 0.

I checked the voltage by placing the voltage meter positive probe on the cable coming out of the back the alternator and the negative probe on earth and I am getting around 11.5 -12V reading. My understanding is it should be kicking out about 15V so i am assuming the alternators soul is on its way to heaven and muggins here is going to have to spend his beer tokens (money) on a new one or is there something else that could be causing this problem that i am not aware of???

Any help appreciated as I am in the dog house because she has been moaning about this for about a month but every time i checked it the engine was cold and i did not see any problems, so when it broke down yesterday on the way to a day of mud plugging lets just say she was not amused when i said dump it, pick it up later and spend the day driving my toy instead which erm isnt as refined as the wrangler

Thanks for any help in advance, Jim

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Old 07-07-2008, 11:20 AM   #2
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I would first check the battery by having a battery shop perform a "load test" on it. A battery with a dead cell can cause all kinds of problems that can appear to be alternator related. But even before doing that, I would remove the battery connectors, clean them thoroughly, and then securely reconnect them and see if that fixes the problem. Way too many problems like yours are caused only by loose/dirty/corroded battery connectors.

I suggest all of the above because the TJ's alternator is actually a very good one and it rarely causes problems. Incidentally, the TJ alternator's voltage regulator is external, it's located inside the engine computer and I haven't ever heard of it ever giving any problems.

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Old 07-07-2008, 12:12 PM   #3
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does it have a battery thermistor? i've seen those cause a similar problem, only after someone replaced the alternator and the computer did they realize it had one.
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Old 07-07-2008, 12:24 PM   #4
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does it have a battery thermistor? i've seen those cause a similar problem, only after someone replaced the alternator and the computer did they realize it had one.
Do you mean a resistor wire? If so, a TJ doesn't use one.
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Old 07-07-2008, 12:36 PM   #5
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the newer grand cherokees have them, its a sensor in the bottom of the battery tray, gm calls it a thermistor, not sure what jeep calls it. the computer uses signal from this as part of its voltage regulating system. i don't think tj has them though.
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Old 07-07-2008, 12:51 PM   #6
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the newer grand cherokees have them, its a sensor in the bottom of the battery tray, gm calls it a thermistor, not sure what jeep calls it. the computer uses signal from this as part of its voltage regulating system. i don't think tj has them though.
That's the temperature sender, it warns the alternator to slow down on the charging if the battery starts getting too hot. Yes it is technically called a thermistor and yes the TJ has one. It won't cause the OP's problem though.
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Old 07-07-2008, 04:50 PM   #7
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i know first hand it can cause a low or no charge condition, like i said i watched a co worker replace the alternator and computer before the thermistor fixed the no charge condition, just a thought on something else to check, i've only seen one go bad in my whole life, but i've also seen them get left unplugged.
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Old 07-07-2008, 05:25 PM   #8
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i know first hand it can cause a low or no charge condition
True but his volt meter also drops down to zero volts when the problem happens which the thermal sensor wouldn't cause.
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Old 07-08-2008, 06:42 AM   #9
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Thanks for all the replies.

I tried a different battery - no change
I cleaned all the connections - no change
I checked there was not a drain on the system
I took the alternator off, gave it a couple of shakes and some twigs, bits of grass, and dried mud came out of just about every oriface.
I then took it to auto electrical shop who spun it up and said it was only producing between 50 and 70 amps, and it was fluctuating quite badly so they said although it is producing charge it is not producing the required 90amps and the fluctuation is not normal
So i have bit the bullet, ordered a new one whilst handing over £237 ($466)

So i am hoping Mr auto electrical is correct and the alternator is the cause of the problem

Jim
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Old 07-08-2008, 07:49 AM   #10
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True but his volt meter also drops down to zero volts when the problem happens which the thermal sensor wouldn't cause.
his volt meter on his dash goes all the way down, but they don't have zero on them, they go down to 10 or 12, and he used a real voltmeter on the alternator to check for voltage, and when his problem occurred he had 11.5 to 12 volts, that can be a symptom of thermistor, acting like a bad alternator, or voltage regulator, causing no charge, although, i already said it is rare, and just something else to think about, sounds like he's got it figured out.

sounds like your alternator, they're not supposed to have a forest in them.
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Old 07-08-2008, 09:48 AM   #11
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Before installing the new alternator, try saving the old one first. When they get packed with mud, dirt, etc., you can often flush all that out with lots of WD-40 which will not harm its electronics. This is done commonly for alternators in Jeeps that see a lot of mud. By a lot of WD-40, I mean a LOT... like one or two can's worth. WD-40 was actually designed to rid electronics of moisture and if you use enough of it, it will do that at the same time it flushes out the contaminating dirt & mud. Shake out the excess WD-40 when you're done flushing it and see how it does.
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Old 07-08-2008, 10:44 AM   #12
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Quote:
Originally Posted by jimbarrettsmith View Post
Thanks for all the replies.

I tried a different battery - no change
I cleaned all the connections - no change
I checked there was not a drain on the system
I took the alternator off, gave it a couple of shakes and some twigs, bits of grass, and dried mud came out of just about every oriface.
I then took it to auto electrical shop who spun it up and said it was only producing between 50 and 70 amps, and it was fluctuating quite badly so they said although it is producing charge it is not producing the required 90amps and the fluctuation is not normal
So i have bit the bullet, ordered a new one whilst handing over £237 ($466)
So i am hoping Mr auto electrical is correct and the alternator is the cause of the problem Jim



$466 for that you could have a Mean Green sitting in there.Is that the price for a replacement stock alternator over there??? Also I had no problems with my stock alt but here recently when I switched it out for the 136amp one from a full size dodge I tested the stock alt and although it never droped below 70amps it did fluctuate from 70-90 amps on the meter.
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Old 07-09-2008, 06:53 AM   #13
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"$466 for that you could have a Mean Green sitting in there.Is that the price for a replacement stock alternator over there??? "


Yep Jeep parts are very expensive in the UK hence my wife drives a wrangler and I drive a suzuki (sorry for swearing ) (oh and I do drive liberty as an every day car ).
In comparison to the 2 vehicles I can buy a complete sidetracker for £200 which is cheaper than most parts for the wrangler hence it really really hurts when the wrangler breaks down. I did search for a different type of alternator and I wish i knew about the mean green one but i wouldnt expect that to be cheap either.

Oh speaking of money i know your Gas prices are rising quite badly but you have a way to go before you catch us up we are currently at $8.95 a US gallon and it is going up weekly
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Old 07-09-2008, 10:33 AM   #14
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Hell with those kinds of prices it would be cheaper to buy a complete "spare" wrangler as your own "Pick & Pull" yard. At least you would have one of everything.
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Old 07-10-2008, 01:52 PM   #15
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Thanks to everyone for your help, the new alternator turned up, it is on and everything is working perfect. And i might be smoking something but I am pretty sure engine is sounding a lot quieter

thanks again for all the help and advise

Jim

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