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Unread 06-15-2008, 12:42 AM   #1
compfreak530
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1988 XJ Cherokee 
 
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90 XJ runs rough

I just got a 1990 jeep cherokee limited 4.0 and it runs really rough. when i drove it home it ran great, but the next day it ran like crap. i found the fuel filter was fully clogged and replaced that with only a little improvement in performance.at first i thought it was a clogged injector so i ran some chevron with techron fuel cleaner through it and nothing. iv checked all the vacuum hoses and they all appear in good shape. as a random boredom test i unplugged each injector while running and found that the front 2 changed nothing, when i unplugged the back 4 the engine almost died. what can i do to test the front 2 injectors? how many volts should be coming out of the injector plugs? it idle`s rough and acceleration is also just as rough. i did a compression test and found that all 6 cylinders were at 125-130 psi.


Last edited by compfreak530; 06-15-2008 at 06:02 PM..
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Unread 06-15-2008, 01:29 AM   #2
littleblackXj
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How long has its been since you replaced the spark plug, wires and distributor? I would start there.
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Unread 06-15-2008, 01:38 AM   #3
compfreak530
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i just it last week, i checked the spark plugs and they all appear to be clean burning. the truck did sit for about a year before i got it. iv herd you guys talk about sea foam. should i try that?
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Unread 06-15-2008, 02:03 AM   #4
littleblackXj
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I would. It costs about $10. Let your engine warm up and leave it running. Then pull off the intake tube and pour it directly into your throttle body. Just make sure to do it slowly and not let the jeep die. Then once you pour in about 1/3 of the bottle turn off the engine and let it sit for 5-10 minutes. Then when you start it up it will burn off all the carbon. Tack it up a bit for a few minutes then drive it around town like you stole it to burn off the carbon diposits.
It produces enough smoke to hide a tank, lol. I took a video of my jeep when i did it: http://youtube.com/watch?v=fwlgjOOl45E (back when it wasnt lifted ).
If you do kill it when pouring it into the throttle body, wait 5 minutes then start it up and then tack it up.
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Unread 06-15-2008, 02:38 AM   #5
compfreak530
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when you say about 1/3 into the engine. do you mean in the oil. or gas. or both?
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Unread 06-15-2008, 10:45 AM   #6
littleblackXj
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I mean pour 1/3 into the throttle body. Don't put it into your oil though. I would put the rest of the can into your gas tank.
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Unread 06-15-2008, 04:33 PM   #7
compfreak530
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I did as you said and got white smoke. not as much as your jeep but still alot. it still idles rough and hesitates on acceleration. after about 3k rpm it smooths out, could it be a vacuum leak?

Last edited by compfreak530; 06-15-2008 at 05:38 PM..
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Unread 06-17-2008, 01:34 AM   #8
littleblackXj
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I am not sure what it could be but ill bump your thread for you
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Unread 06-17-2008, 07:14 AM   #9
balloo93
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How much gas was in it while it sat for a year? The gas more than likley went bad and you should go ahead and drop the tank and replace the fuel pump. Then run some seafoam in the gas to clean the fuel lines and injectors.

After that, I'd replace the plugs.
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