4.0 still having power issues, battery gauge moving up and down.. - JeepForum.com
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Unread 02-04-2013, 01:30 PM   #1
Candymancan
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1998 ZJ 
 
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4.0 still having power issues, battery gauge moving up and down..

So the 4.0 has been having issues for awhile now where the battery voltage would go from say 14 to 0 and it would say check gauges.... Then eventually it start up at 12v and then slowely drop to 0.. I swapped batterys drove it to advance auto and my old alternator was putting out no power... So i got a new alternator and boom worked like a charm..

Now tho aparently the voltage is playing tricks again except this time its going from 14v when its started and shooting up to 19v.. then dropping back down and saying check gauges.. Im at my wits end here.. what is the problem... Is the voltage regulator in the PCM going bad or something ???..

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Unread 02-04-2013, 01:45 PM   #2
massarosareloud
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Just a thought, there is a battery temperature gauge. It sits directly underneath the battery and regulates the voltage for recharging based on temperature. I wonder if it isn't reading correctly anymore and causing the PCM to throw crazy amounts of power back at the battery to try to charge it. I would wait for a more experienced Jeeper to voice their opinion, but it is something to look into.
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Unread 02-05-2013, 01:54 PM   #3
Candymancan
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can someone please help me... If the voltage is going from 14 to 19v then dropping to 0 and making the dashlights flicker... what is the problem ??? Is it the regulator in the PCM ??

Shall I go to a JY and pull a PCM off a 4.0 ? Which years would be compatible with my 98 ? Im guessing 96-97-98 right ? any OBD2 from a 4.0 ?
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Unread 02-05-2013, 02:26 PM   #4
um7267
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not to sure about the temp sensor, but did you try checking your main lines to the alternator? mines all gummed up with crap and needs cleaned so maybe so some oil got down there on you
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Unread 02-05-2013, 02:34 PM   #5
Candymancan
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Cables to the battery and from the alternator look fine.. In fact i cut off the old connectors to the battery and cleaned up the cable and put new connectors on.. It has a brand new alternator as well... Can a bad battery cause the voltage to go from 14-19 ?? The battery is about 3-4 years old, and was being charged with a dying/bad alternator for quite some time... I also noticed it leaking Juices out of the plugs up top last year almost like it was being overcharged..
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Unread 02-05-2013, 05:38 PM   #6
herqulees
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ECM voltage regulator has nothing to do with the Jeep's power at all, all it does is turn the 12volts from that battery to 5volts for the ECM to run on.
The battery temp sensor I know very little about... how a tiny sensor barely touching the bottom of a huge car battery can give the Jeep even a tiny hint to what it's temp is is beyond me, but after some Googling it looks like that when that sensor starts going bad some weird voltage issues can arise.
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Unread 02-05-2013, 06:00 PM   #7
Candymancan
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I know you are completetly wrong on the PCM.. The PCM has the voltage regulator built into it for the alternator.. Most car alternators have regulators built into them.. The PCM on Jeeps have it built into the computer... When the Regulator goes bad the voltages on the alternator go crazy and can overvolt the system.. You are right in the sense that the PCM has a 5v regulator in it, but it also has the alternator's regulator in it as well, the PCM regulates the alternator to charge the battery... If it goes bad it starts to overvolt everything

Look it up if you dont believe me...


Anyway since no one on this forum can help me i found a fix on google after searching all day.. Im going to install a external regulator to the alternator and battery and disconnect the pcm from the alternator in short im going to bypass my PCM's regulator this way I dont have to look for a junkyard PCM and hope it works, or buy a $250-300 new pcm.
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Unread 02-05-2013, 06:16 PM   #8
herqulees
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Quote:
Originally Posted by Candymancan View Post
I know you are completetly wrong on the PCM.. The PCM has the voltage regulator built into it for the alternator.. Most car alternators have regulators built into them.. The PCM on Jeeps have it built into the computer... When the Regulator goes bad the voltages on the alternator go crazy and can overvolt the system.. You are right in the sense that the PCM has a 5v regulator in it, but it also has the alternator's regulator in it as well, the PCM regulates the alternator to charge the battery... If it goes bad it starts to overvolt everything

Look it up if you dont believe me...


Anyway since no one on this forum can help me i found a fix on google after searching all day.. Im going to install a external regulator to the alternator and battery and disconnect the pcm from the alternator in short im going to bypass my PCM's regulator this way I dont have to look for a junkyard PCM and hope it works, or buy a $250-300 new pcm.
Well I learned something new about my Jeep.
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Unread 02-05-2013, 06:37 PM   #9
ZeeJay1997
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Quote:
Originally Posted by Candymancan View Post
can someone please help me...
If you can find a friend that will let you put a different battery in it to see if you get different results, you'll be way ahead. Click green link below. Go to #4. Click blue link.
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Unread 02-05-2013, 07:03 PM   #10
ZeeJay1997
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Quote:
Originally Posted by massarosareloud View Post
Just a thought, there is a battery temperature gauge. It sits directly underneath the battery and regulates the voltage for recharging based on temperature. I wonder if it isn't reading correctly anymore and causing the PCM to throw crazy amounts of power back at the battery to try to charge it. I would wait for a more experienced Jeeper to voice their opinion, but it is something to look into.
This shouldn't cause the gauge to drop to 0, but you want to eliminate it as a cause, unplug it.
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Unread 02-05-2013, 09:17 PM   #11
Candymancan
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Yea we have three cars.. 2 ZJ's in the sig and a 2013 camaro SS.. I'll just swap batteries from my 5.9 over to it then. The thing is its so random.. It doesnt just happen right awya one day its ok the next its not
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Unread 02-06-2013, 08:32 AM   #12
massarosareloud
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Maybe some broken solder points somewhere? Maybe in the PCM?
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Unread 02-06-2013, 09:11 AM   #13
McCloudsZJ
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Quote:
Originally Posted by Candymancan View Post
I know you are completetly wrong on the PCM.. The PCM has the voltage regulator built into it for the alternator.. Most car alternators have regulators built into them.. The PCM on Jeeps have it built into the computer... When the Regulator goes bad the voltages on the alternator go crazy and can overvolt the system.. You are right in the sense that the PCM has a 5v regulator in it, but it also has the alternator's regulator in it as well, the PCM regulates the alternator to charge the battery... If it goes bad it starts to overvolt everything

Look it up if you dont believe me...


Anyway since no one on this forum can help me i found a fix on google after searching all day.. Im going to install a external regulator to the alternator and battery and disconnect the pcm from the alternator in short im going to bypass my PCM's regulator this way I dont have to look for a junkyard PCM and hope it works, or buy a $250-300 new pcm.
I'm a little sorry I didn't see this thread sooner. It definitely sounds like a bad regulator, and you're right, it's in the PCM and NOT in the alternator. I was talking to a fellow who owned a shop that rebuilt alternators about getting a 150A alternator for my 5.9 rebuilt. He said that he'd owned 9 Grand Cherokees (all ZJs and WJs), and had put external regulators on all of them. I'm thinking about getting it done preemptively. It'd be the fastest and easiest way to fix your problem.
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Unread 02-06-2013, 05:48 PM   #14
Candymancan
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Thats what im gonna do... Im buying a $20 regulator from autozone, some 14gauge wire, and ring terminals and butt plugs, and a wire harness and im gonna do exactly what its in this thread. Not just fastest and easiest, but also cheapest way should only cost like $60 for all the parts i need, vs $150 for the computers in local junkyards that arent even garunteed to work.. and $250 for a new one.. Only downside is the check engine light it will cause


http://dodgeforum.com/forum/2nd-gen-...onversion.html
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