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Unread 10-04-2013, 11:38 AM   #1
daven75
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possible alternator problem

My volt gauge just shot all the way up to 19 multiple times and I got the check gauges light. Any ideas?

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Unread 10-04-2013, 12:16 PM   #2
tjwalker
It's the crank sensor!
 
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What year/engine? There are significant differences along the way so gotta get that information in your thread and also good idea to fill out your profile.

When I see this, first thing I do is to verify with a meter and a simple measurement across pos. and neg. battery cables.

If real, then the problem could be the alternator. On earlier models through 1990, the voltage regulator is not integrated into the computer and is also high on the suspect list.
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Unread 10-04-2013, 01:06 PM   #3
daven75
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Its a 2000. I just had the alternator checked at advanced auto parts and it passed. Battery also checked out fine as well
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Unread 10-04-2013, 01:32 PM   #4
tjwalker
It's the crank sensor!
 
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Passing that test at Advance Auto doesn't guarantee that your alternator is good. Those parts stores testers are famous for "escapes" (testing good when part is bad). I've seen it quite a few times.....
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Unread 10-05-2013, 12:11 AM   #5
daven75
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I'm not sayong that cause it passed that its not the problem, I'm just saying its better than me staring at it going, yea i think its fine.
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Unread 10-06-2013, 01:25 PM   #6
JWELK
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The regulator is in the PCM. When my 99 did that it was the PCM providing a constant ground to the field. However it wasn't intermittent, once it failed it stayed failed. The PCM regulates the negative side of the field, the other side is hot, via the ignition. It is not like the "old days" where the alternator is either on or off, but it is called Pulse Width Modulation. When working properly it charges the battery much more efficiently, it also means you need an oscilloscope to monitor it. For the alternator to be bad, this wire and this wire only must be shorted to ground, internal on the alternator, possible but very unlikely. On my 99, it is the Dark Green wire on the PCM center plug B10. I just looked this up on my FSM and it lists this pin as the Generator Driver+, but two other schematics and memory say that it is in fact the Generator - pin. You can verify it on your generator plug, the other wire will be 12 volts with the ignition on. It is possible the PCM is intermittent, but unlikely, you may have a chafed cable. At any rate, I read on another site the - Battery lead should be disconnected for a moment or so before removing plugs from the PCM. I don't recall if this was for 99 only or all of them. The reasoning was when the battery is disconnected, instructions get written to the uprocessor for retention, when you pull the plug those instructions may get corrupted resulting in an unrecoverable failure.
I would refrain from using the stereo and other "electronical" accessories until you get this resolved, in fact I wouldn't drive it other than to the mechanic. I took out a channel on the stereo and I'm certain it contributed to, if not caused my ignition coil to crack.

Regards,

Jim W
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Unread 10-06-2013, 04:23 PM   #7
Holder350
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Check the harness going to the alternator for chafing and spots where the dark green wire could be shorting to ground.

If you cant find anything wrong, i would replace the alternator.

If the problem persists you'll have to swap the PCM.

Or we can walk you thru installing an external regulator to drive the alternator.
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Unread 10-15-2013, 11:57 PM   #8
jeff540
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Quote:
Originally Posted by Holder350 View Post
Check the harness going to the alternator for chafing and spots where the dark green wire could be shorting to ground.

If you cant find anything wrong, i would replace the alternator.

If the problem persists you'll have to swap the PCM.

Or we can walk you thru installing an external regulator to drive the alternator.
Had my regulator go out years ago,had a shop rebuild and install internal VR.been fine for years now it is out again,would like to know if you can walk me through installing an external VR. what's a good one,adjustable voltage worth the extra bucks or not. found C8313 chrysler from 70's up to 90's may be worth a shot.

sorry for the hijack.
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Unread 10-16-2013, 12:22 AM   #9
Holder350
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http://www.jeepforum.com/forum/f11/e...-asap-1167297/

You can post here, there or PM me with any questions.

Sent from my phone where correct grammar is difficult.
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Unread 10-16-2013, 08:54 AM   #10
jeff540
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Quote:
Originally Posted by Holder350 View Post
http://www.jeepforum.com/forum/f11/e...-asap-1167297/

You can post here, there or PM me with any questions.

Sent from my phone where correct grammar is difficult.

Thank You! when I pick up the regulator,if I have any problems,I will repost.

I posted on another jeep forum,and was told if my alternator is not charging,it is the votage regulator, I always thought that if my gauge was reading high (18/19) THAT was a sign the VR was the problem. now I was told by a very smart person on the subject on the other forum,that low voltage would mean bad VR.If high voltage it is a bad diode or rectifier problem. I did find a bad rectifier in my alt.changed it out,still same low voltage.next step VR.
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Unread 10-17-2013, 10:24 AM   #11
JWELK
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The "very smart person" on the other forum needs to go back to High School basic electricity. If in fact that were true, why would an engineer install extra diodes. The problem can be either the alternator or the VR. I had a similar issue in the my 99 and it was the PCM. Holder 350 is correct. Look for a ground on the Dark Green wire, if it is not shorted there are only 2 possibilities an internal short in the alternator of a defective PCM. As you had the alternator tested and I can only ASSuME they found no internal shorts, that leaves only the PCM.
You can install an external regulator, however, you may find other unexplainable issues. Maybe Que has additional info. With uprocessors, disabling inputs and outputs can lead to mysterious issues. I would lean toward an shorted Dark Green wire as the problem is intermittent, when uprocessors and other electronic components fail, they normally aren't intermittent, but fail permanently. The exception is heat, sometimes connections both on the PCB and internal to the component fail when they expand due to heat. Does this occur only when warm or randomly?

Regards,

Jim W
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Unread 10-17-2013, 01:43 PM   #12
jeff540
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Quote:
Originally Posted by JWELK View Post
The "very smart person" on the other forum needs to go back to High School basic electricity. If in fact that were true, why would an engineer install extra diodes. The problem can be either the alternator or the VR. I had a similar issue in the my 99 and it was the PCM. Holder 350 is correct. Look for a ground on the Dark Green wire, if it is not shorted there are only 2 possibilities an internal short in the alternator of a defective PCM. As you had the alternator tested and I can only ASSuME they found no internal shorts, that leaves only the PCM.
You can install an external regulator, however, you may find other unexplainable issues. Maybe Que has additional info. With uprocessors, disabling inputs and outputs can lead to mysterious issues. I would lean toward an shorted Dark Green wire as the problem is intermittent, when uprocessors and other electronic components fail, they normally aren't intermittent, but fail permanently. The exception is heat, sometimes connections both on the PCB and internal to the component fail when they expand due to heat. Does this occur only when warm or randomly?

Regards,

Jim W
My alternator has an aftermarket VR in it now,which I think is faulty.my PCM voltage Reg quit years ago.so i am not using the Dark Green wire,or pcm wires.

want to add fender mounted or firewall mounted VR,purchased BWD r296p VR last night,was special order should be here sometime today,ordered the plug for it also. 23.00 for both. my question is are the bwd 296p vr's 12V A-circuit or 12V B-circuit. I need 12V A-circuit,the salesperson could not find that info,and google is no help either.
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Unread 10-17-2013, 06:59 PM   #13
daven75
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OK guys, this is a small update, its weird, I dont get it. I replaced grounds, and the battery temp sensor, started with the cheapest things first. Now, it still does it, I was able to rev the engine at 2k rpm's and it triggered the check gauge and the 19V reading BUT I checked the voltage at the cig outlet and it read no more than 15v. It hit that like once but only for less than 1 second.

I'm at a loss.
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