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Unread 07-29-2013, 06:37 PM   #1
maroon87xj
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87 4.0 auto problems

hey guys and gals, i have owned this cherokee now for 3 months. first time jeeper on ur hands here... i call my jeep the p. s the p ran fine but had a rough idle so i went ahead and did a tune up. cap rotar plugs wires oil filter and change. in doing that i found a vaccum leak and fixed. i was all excited cause i did my first tune up on the ol p... so then the problems start. my fuel gauge gets tapped out over full. then my alternator ges out so i get a new one and replaced it. ooh and a new fuel filter. nw the jeep has left me stranded 4 times with dead batterys but the alt tests fine. i have cleaned all the grounds i can. switched batterys in it and does the same thing.this jeep has got me stumped and i know little to nothing about working on cars. i have looked on here for weeks and done a few things here and there. sorry to babble on any help would be great

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Unread 07-31-2013, 10:37 AM   #2
psychoteen101
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Quite possible the voltage regulator in the jeeps computer went bad. Try swapping in a new computer to varify to save you from buying a new one if its not at fault
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Unread 07-31-2013, 12:53 PM   #3
maroon87xj
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ok great thank you for the advice. i will look around and see if i can find one for cheap or if a buddy has one i can use for a day... would a bad brain cause the jeep t drain the battery?
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Unread 07-31-2013, 02:05 PM   #4
psychoteen101
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drain the battery from just sitting? it shouldnt. you might have some sort of a draw on the battery that causes it to drain. you can do a parasitic drain test if you have a multimeter. go on youtube and search how to do it, will give you a tutorial on how to check it yourself.
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Unread 07-31-2013, 03:01 PM   #5
maroon87xj
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yea i put a new alternator in the jeep and had it tested b4 i left the parts store also paid more for a lifetime warrenty. and its like the alt isnt charging when i drive. cause after a couple days of driving it will be at like 11 volts and wont crank over. i charge the batt for a while and its good for a couple more days. i cant see no bad wires or bare. iv cleaned all the grounds and replaced the main one from the motar to the chassis. i thought it was maybe the stereo i had instaled draining the juice so i took that out and the problem still lingers on.. it has got me stumped
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Unread 07-31-2013, 05:08 PM   #6
psychoteen101
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Does the guage on the cluster show that its charging? Is the battery light on while running? Check voltage at the battery while its running to make sure the alternator is puting out the correct charge. It sounds like you possibly have something thats draining your battery. If the alternator is sending good voltage to the battery, do a parasitic drain test to see if something is drawing amperage while the jeep is shut off.
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Unread 07-31-2013, 07:32 PM   #7
maroon87xj
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none of my lights in the cluster are working atm. my tach does and thats it. fuel gauge is tapped out past full and when i start her up no lights cycle. i have load checked the battery its fine. and the volts while alt is charging are normal.. i will look into that test over the weekend when i got some time hopefuly
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Unread 08-05-2013, 04:07 PM   #8
psychoteen101
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Could be a wiring issue lingering as well if a majority of the cluster isn't working. But either way, check the parasitic draw and try and swap ECU's to see if the voltage regulator is at fault.
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Unread 08-05-2013, 04:59 PM   #9
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Quote:
Originally Posted by psychoteen101 View Post
Quite possible the voltage regulator in the jeeps computer went bad. Try swapping in a new computer to varify to save you from buying a new one if its not at fault
In 1987, the regulator is inside the alternator, and does not rely on the ECU. Don't change the eCU. .
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If you own a Renix Jeep, you'll want to check this out. >

An index to over 25 write-ups can be found in Post #1.

Cruiser's Mostly Renix Tips
Refresh*Connections*Before*Replacing*Components
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Unread 08-05-2013, 05:25 PM   #10
psychoteen101
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^ wasnt sure if it was or not, thanks for the confirmation.
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Unread 08-05-2013, 05:31 PM   #11
cruiser54
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Quote:
Originally Posted by psychoteen101 View Post
^ wasnt sure if it was or not, thanks for the confirmation.
91 went PCM. His alternator could have a bad diode pack/bridge.
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Quote:
Originally Posted by chris87xj View Post
If you own a Renix Jeep, you'll want to check this out. >

An index to over 25 write-ups can be found in Post #1.

Cruiser's Mostly Renix Tips
Refresh*Connections*Before*Replacing*Components
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Unread 08-06-2013, 11:52 AM   #12
psychoteen101
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Im still curious as to if its a charging system issue or if hes just having problems with the battery draining after the jeep is shut off.
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Unread 08-12-2013, 01:02 AM   #13
maroon87xj
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I have been busy with work lately, been using a spare vehicle for work. I looked up how to do the parasitic test and plan on doing it soon. I will let you all know the results. Thank you for all the help!!
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