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Unread 12-09-2009, 10:15 PM   #1
adudenamedsean
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bad alternator vs bad battery..

Hey everyone, sorry if this turns out to be a long post, but I've been running on very little sleep due to exams. haha.

Over the past few days, I've noticed my jeep starting to act funny electrically. It just seemed to have a weak battery. For example, with the Jeep turned off and my dome light on, I could mash the brake pedal and when the brake lights lit up, my interior lights would dim. But it always started fine, never really hesitated or anything.

That was until today. After my exams today, I came out to the Jeep and went to start it and I had no power whatsoever. No dim lights, no clicking when trying to start, nothing. I thought for sure my Jeep had passed away on me Well it finally started after jumping it off for a while. At first, it didn't want to run on its own, I had to keep it idled up or else it would stall. On the way home, I hopped on the interstate, and next thing I know, my voltage on the dash is pegged at 19+ with my warning light yelling at me.

So I limp it home, and shut it off for the night, and try to start it again. same deal. absolutely nothing.


so what do you guys think it is? battery kicked the bucket (Its about 3 years old, so a possibility), or is it a bad voltage regulator in the alternator. I've just never heard of a bad battery spiking with high voltage. Or has my alternator gone bad, in turn, frying my battery?


I'm just confused and I really can't afford to start throwing too much money at the Jeep aimlessly. Thank Y'all!!

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Unread 12-09-2009, 10:25 PM   #2
riscal33
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Check all your contacts.....make sure they are "shiny" clean any corrosion could cause a short.....Mine just did the same thing it was a loose clamp on negative terminal.
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Unread 12-09-2009, 10:25 PM   #3
Jerry Bransford
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Start by removing your battery connections and using a wire battery brush, clean the inside of the connections and battery posts. Then securely reinstall the battery connections. Most problems like yours are caused by nothing more than a bad battery connection. If that doesn't do it, 99% chance it's a bad battery and not a bad alternator.
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Unread 12-10-2009, 05:53 AM   #4
BigRigoTJ
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Clean battery posts and terminals. Get a volt meter and if you can get the motor running, check voltage at the battery while the engine is running. You should see 13.80 to just over 14 volts. if not then bad alternator or bad connections at alternator. If you see good voltage then bad battery.
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Unread 12-10-2009, 05:55 AM   #5
BigRigoTJ
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Oh and if it's cold out side and the batt is old that is a factor as well. Old batteries and cold weather do not go well together. My honda's batt went out because of it.
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Unread 12-10-2009, 06:44 AM   #6
blkbetty02
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Quote:
Originally Posted by Jerry Bransford View Post
Start by removing your battery connections and using a wire battery brush, clean the inside of the connections and battery posts. Then securely reinstall the battery connections. Most problems like yours are caused by nothing more than a bad battery connection. If that doesn't do it, 99% chance it's a bad battery and not a bad alternator.
I agree. It's probably a bad battery. Take your battery out and run it down to any auto parts store (napa, autozone, advance) and they'll test for ya, for free.
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Unread 12-10-2009, 08:17 AM   #7
Max-Q
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Go to Autozone and have them test your battery and altenator. It sounds to me like the voltage regulator in the altenator is bad.
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Unread 12-10-2009, 08:40 AM   #8
TJaefick
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Quote:
Originally Posted by Jerry Bransford View Post
Start by removing your battery connections and using a wire battery brush, clean the inside of the connections and battery posts. Then securely reinstall the battery connections. Most problems like yours are caused by nothing more than a bad battery connection. If that doesn't do it, 99% chance it's a bad battery and not a bad alternator.
Do exactly what he said, but when you have the wires off the battery, it's worth hooking it up to a trickle charger over night. I was having similar problems, and while an alternator does technically charge your battery, that isn't their primary purpose and they aren't very efficient at it. One night on the charger and all of my problems were solved. (Well, not all of my problems, but the ones related to the jeep not starting )
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Unread 12-10-2009, 09:43 AM   #9
Max-Q
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Quote:
Originally Posted by TJaefick View Post
Do exactly what he said, but when you have the wires off the battery, it's worth hooking it up to a trickle charger over night. I was having similar problems, and while an alternator does technically charge your battery, that isn't their primary purpose and they aren't very efficient at it. One night on the charger and all of my problems were solved. (Well, not all of my problems, but the ones related to the jeep not starting )
This all true but why would the voltage spike to 19+? The only time I've ever seen this happen it has been the voltage regulator on the altenator not the battery.
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Unread 12-10-2009, 10:18 AM   #10
Strizzy
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Voltage regulator is part of the PCM on a TJ, not the alternator.
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Unread 12-10-2009, 02:39 PM   #11
adudenamedsean
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thanks for the help everyone! I've cleaned up the battery terminals and everything, and it still won't keep charge, so i think I'm going to try just replacing the battery. Now, as most jeepers would do, I'll use this as a reason to upgrade to either the optima or the die hard platinum. I seem to be leaning toward the die hard per all the great reviews, including yours Jerry. But one question, possibly a stupid one, is the platinum conidered a dry cell battery? I wanna go with tnt tubes in the future and they require a dry cell.
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Unread 12-10-2009, 03:00 PM   #12
diablo_331
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Check you Big 3 wires. alt+ to Batt+,Batt- to engine block-,Batt- to Chassis-.Clean up all of the connections nice and good. If you decide on a new battery that I would highly suggest a Sears Diehard Platinum.
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Unread 12-10-2009, 03:02 PM   #13
freeskier93
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This happend to me when I accidentally drained my battery. Like everyone else said, try cleaning the terminals. Also let it trickle charge. For some reason when the battery gets totally drained it resets the ECU and has to re "learn" how to idle. After about a week it works itself out.

So don't be surprised if it still won't idle after cleaning the terminals or even buying a new battery.

Oops, I guess I should have finished reading all the posts, but still try trickle charging over night before you go buy a new battery.
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Unread 12-10-2009, 03:06 PM   #14
jonnyz123
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sounds like alternator to me. pull it and the batt and have them both tested for free at autozone.
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Unread 12-10-2009, 03:25 PM   #15
w9kh_kevin
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Whichever it is, have each of them tested at whichever your parts store of choice may be. That is the best way to go about it. You could keep guessing, but they will be able to give you an answer.
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