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Discussion Starter #1
hey guys got a question for you's
Ok. Sounds decent. Has been used off road. Has a pretty nasty bend in the leaf spring and mud caked underneath. But that is not the problem. The jeep will run perfectly for about 10 minutes then start to bog down and back fire pretty bad.I originally thought it was running hot and that was causing it but the thermostat fan and radiator are doing their job. It did have a cracked valve cover and thought it mighta been bringing air in through there.did a temporary fix with some rtv silicone til i find the new valve cover.But it is still doing the same thing. Also it should idle at 850-900 but it keeps bumping back up to 1200-1500. It's an 89 YJ with a 2.5 litre in it. Any suggestions??
 

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The same thing happened to my 89, 4.2. after approx. 10-15 minutes. I had a bad Ignition Control Unit. I replaced it and that solved the problem. It now runs great. Some say it either works or doesn't work, but that wasn't the case with mine.
 

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Discussion Starter #3
heres a list of some of the stuff that was replaced on my jeep before i bought it
new radiator,water pump,160 thermostat,new fuel tank,fuel pump,strainer,plugs,wires,distributor,new wiring for ignition,exhaust manifold and studs,new shocks all around,new air filter,if and when it act's up,i shut it off,leave it sit for 5 minutes and its fine for about another 20-30 min?it sure has me stumped,but im thinkin either fuel filter or 02 sensor
 

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I'm not sure if the 4 cyl. has one, but it probably does, so check under the coolant expansion tank for the box. It's held on with 3 10mm bolts and easy to replace. Most auto stores stock them. I bet that is your problem. Age and heat causes them to fail, that's why you're o'k when cold. Probably not fuel filter or O2 sensor, although the O2 sensor should be replaced after 88,500 miles, as per the manual. I really believe that if you replace the Ignition Control Module you will solve your problem.
 

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Discussion Starter #5
any other suggestions anyone??possibly a computer?also would the catalytic converter cause this??
 

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so when its running fine, where does it idle at before it go's bad? I think your on the right track with the o2 sensor or fuel filter..
 

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Discussion Starter #7
fuel filter was just replaced...it idles around 1300 at all times,i turned the screw to lower it,it lowers if i floor it but goes right back up to 1300 sometimes higher as soon as i move it or it idles for over a minute
 

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one good place to check is your spark plugs take them out and see if there misfiring. i see that you just replaced it but it be good to just check them , also did you ever do a engine flush?when was you last oil change and what vesocity?
 

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Discussion Starter #9
plugs looked good when we checked them last week,no build up or anything,although i didnt check the gap to make sure its correct,oil was changed right before i got it with 10w30,but another thing that kinda has me confused,is when its cool out like in the morning,truck runs great no matter how long i drive it,it seems to act up when its around 80 outside with humidity
 

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I was havong the same trouble, I replaced the map sensor, and just about everything else. Then I replaced the computer, bought the new one for $90 at Advance Auto Parts. and now it runs great. BTW, sometimes you get a bad computer from the store, I know becuase I put it in and it did the same thing. Took it back and got a replacement, and it is perfect. Hope this helps.
 

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Discussion Starter #11
ill have to call autozone tomorrow and see how much they are there,i need to go there anyway to get some stuff for my explorer
 

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Not to beat it to death, but if you replace the Ignition Control Module (spark box,computer, etc.) whatever you want to call it your problem will be solved.
 

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hey i had the same problem check out my thread [EXPERIENCED TPS ADJUSTMENT] i think you will find it helpfull:punk:
 

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Its in the dist .Im not sure thats it, with in the last 6 mos Ive touched every part on my 2.5 at least 3 times (3 engine changes ) all for different reasons.This sounds like a slight vacume leak.Check your intake bolts The last eng. i put in ,for some reason I missed the last bolt .started engine and it reved to [email protected] If it detects any sort of lean burn (to much Air) It will automaticly shoot more fuel.
I took aprt the the 3 rd eng. and found the int/exst.gasket blowed between 3rd 4th cyl .the exst can burn up the gasket and the chambers are so close together it can affect the intake.In my short time of being a frustrated jeep owner Ive seen alot .
F-dup wristpins ,cam ground up lifters ,wipedout main bearings.different year plugs not compatable with ignitions.and all in our beloved 2.5
It reminds me or the AMF Iron heads and shovel head Harley engines (good but cantankeruss)
 

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Mine just got out of the shop and was doing the same thing. On the 2.5 there is a crank sensor that sends a signal to the TBI unit (your injector) that tells it when to release fuel. If it is bad- it will still run but will cough and sputter when it cannot read the signal. After they pulled mine it was covered in oil and gunk and was hard as a rock. They replaced it and wallaaa.. it is running like a champ! I even have more power now and can actually use 5th gear again on the highway. -- used to bog down..
 

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I agree with crtaylor, its sounds like a vacuum leak if you cannot adjust the idle and it gets worse as the engine gets warmer. If all bolts and hoses are secure, try some carb cleaner and spray it around all the possible places you could have a leak, if you find the leak, the RPM will change.
 
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