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4 Wheel Drive/SUVs/98 Jeep Cherokee runs rough at idle

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Expert: - 8/17/2009


Question
I have a 98 jeep Cherokee that had a bad water pump and overheated.  After replacing the pump, it runs rough at idle.  I did replace the o2 sensor during a muffler change but that didn't fix the idle.  It runs fine at higher rpm but at idle it runs very rough and sometimes cuts off.

Answer
John,

You said that you over heated the engine.  Did you change the plugs, and give it a good tune up.  If you did this, and it still runs rough, I would run a compression test to see if you may have scored a cylinder wall, ruined some valves, or did other damage to the engine.  Depending on how hot it got, you may have warped a head, or ruined a head gasket.

You should consider having an electronic diagnostics on the engine to see if any sensors or other engine components may have been damaged from the heat.

Other components to check are the throttle position sensor, crank position sensor, along with checking all wiring to see if there was enough heat generated to ruin some insulation causing a short.

Carl

4 Wheel Drive/SUVs

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Carl Brandt

Expertise

Will discuss suspensions, lifts, lockers along with tire suggestions. Trail ratings and possible requirements needed for specific type of trails. Safety equipment and what you should carry with you. Certified off-road instructor. I am not a mechanic, and 4-Wheeling is a hobby, so if I can't answer a technical question it is due to my mechanical knowledge being related to vehicles that I have owned, or have worked on. I do not have manuals on all vehicles.

Experience

40 plus years of 4 wheeling in a variety of vehicles. At the present time, my major off-road rig is a 94 Jeep Wrangler with a spring over and a 1 1/2" suspension lift. This gives me a total lift of 7" or so. I have lockers front and rear. I have removed the track bars, and sway bar for maximum articulation. I am running a stock 2.5 ltr 4 cylinder with a Jacobs ignition along with a cold air high flow filter. It has 4.56:1 gears with a Dodge NV4500 transmission along with a 3.8:1 Atlas II transfer case. This gives me a final ratio of 105:1 in low gear/low range. Other vehicles I own, are a 96 Ford F-250 with a 6" lift, posi rear end, 36" Hummer tires, 5 speed with a fuel injected 460 ci engine, an 87 Samurai with an 8" lift, Ford 9" rear end with a spool, Chevy Dana 44 front end with an electric locker, 5.88 gears, 16% reduction in high range and a 6.5:1 low range with 35" Baja Claws, and a stock 2003 Grand Cherokee Overland. Trails I have run are the Rubicon (10 times), Dusey Ershim, Fordyce Creek trail, McGrew trail, several trails in Moab, Utah along with local monthly runs.

Organizations
Lost Coast 4x4's Cal 4-Wheel Corva UFWDA Blue Ribbon Coalition

Education/Credentials
Certified off-road instructor - Certificates in engineering/electronics

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