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1993 xj idles down after being at high rpm for too long

Old 04-16-2019, 09:02 PM
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Default 1993 xj idles down after being at high rpm for too long

I have a 1993 Jeep Cherokee country edition that I use as a mud bogger, itís completely stock other than lift, tires and snorkel. The problem is that we race in 200 foot long pits and after about 150 feet at about 3500rpms it idles down to about 900rpms for about 5 seconds before I can rev it back up. To me it seems like computer issues but if anyone else has any ideas let me know!
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Old 04-17-2019, 11:17 AM
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How wet is the engine getting? The TPS, for example, can go bad when it gets wet. Mud getting into the alternator is another problem. Could the belt be slipping a bit if its getting showered with mud? I dont take mine mudding, so i dont know how the belt gets affected by it. But the TPS and alternator could be an issue. Or perhaps its just got so much mud around it, its getting bogged down. It is a mud "bog", afterall..

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Old 04-17-2019, 11:21 AM
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Default Water proofing

Originally Posted by fb97xj1 View Post
How wet is the engine getting? The TPS, for example, can go bad when it gets wet. Mud getting into the alternator is another problem. They dont like it.
I do have the entire underside of the engine bay coated with bailer belt so nothing much gets in there and itís more mud than water. To me itís really like the computer tells it that itís been at those rpms too long and sends it back to an idle.. I will look into the tps sensor though. Maybe do some more water proofing.
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Old 04-17-2019, 11:41 AM
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Originally Posted by Mudbogger#5 View Post
I have a 1993 Jeep Cherokee country edition that I use as a mud bogger, itís completely stock other than lift, tires and snorkel. The problem is that we race in 200 foot long pits and after about 150 feet at about 3500rpms it idles down to about 900rpms for about 5 seconds before I can rev it back up. To me it seems like computer issues but if anyone else has any ideas let me know!
By "idles down", do you mean that while you are still on the gas pedal, desiring around 3500 rpm, it only produces around 900rpm?

I ask because that isn't idling, and your engines RPM is primarily commanded by you and the gas pedal - not the computer. If your foot is pressing the pedal, the computer can not override your control of the air entering the combustion chamber, it can only decide to not add fuel or to turn of the ignition.
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Old 04-17-2019, 11:45 AM
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Default Idling down

Originally Posted by jordan96xj View Post
By "idles down", do you mean that while you are still on the gas pedal, desiring around 3500 rpm, it only produces around 900rpm?

I ask because that isn't idling, and your engines RPM is primarily commanded by you and the gas pedal - not the computer. If your foot is pressing the pedal, the computer can not override your control of the air entering the combustion chamber, it can only decide to not add fuel or to turn of the ignition.
Thats what Iím not understanding because when it decides to do this I can have my foot to the floor and still it sits at about 900rpms for a little bit then after a few kicks of the gas pedal it decides to go again. And it isnít like itís running rough when it idles down either, it just sits there running nicely.
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Old 04-17-2019, 11:59 AM
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Check to ensure that your gas pedal cable is free and clear, and clean. Because it sounds like your throttle plate is closing, even though you are on the pedal (because you say it is still running nicely). Because if it was cutting fuel on you, I would think you would get stalls, misfires, etc (due to lots of air, and very little fuel).

To summarize, the running RPM of the motor is primarily controlled mechanically, by the amount of air being allowed through the throttle body. When not idling, this is purely mechanical, and is between the gas pedal and the throttle body. It is not computer controlled, unless your foot is entirely off the pedal, then the computer will start adjusting the IAC to let a small amount of air in and maintain idle RPM (around 750-850-ish).
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Old 04-17-2019, 12:02 PM
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Originally Posted by jordan96xj View Post
Check to ensure that your gas pedal cable is free and clear, and clean. Because it sounds like your throttle plate is closing, even though you are on the pedal (because you say it is still running nicely). Because if it was cutting fuel on you, I would think you would get stalls, misfires, etc (due to lots of air, and very little fuel).

To summarize, the running RPM of the motor is primarily controlled mechanically, by the amount of air being allowed through the throttle body. When not idling, this is purely mechanical, and is between the gas pedal and the throttle body. It is not computer controlled, unless your foot is entirely off the pedal, then the computer will start adjusting the IAC to let a small amount of air in and maintain idle RPM (around 750-850-ish).
that makes sense! Iíll look into that! Thanks for your input
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