Cherokee Owners,...A little help,...pleaze

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jaimus

jaimus

Old School ASE Gold
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Oct 12, 2010
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Hadlyme, CT, USA
Tryin to figure out why my old dependable 99 4.0 Cherokee has a lean dead spot when It goes from closed to open loop,...feels like its goin way lean for about 1/2 mile or 30 seconds or so,(coughs and backfires through the throttle body). Rain or shine. Doesn't stall, but It wants to,..Revs great when I depress the clutch. Put a scanner on It,...No Codes or engine light,....O2 is switching fine,...Distributor pick-ups are intact,...mileage is good,...no black smoke. Has new plugs, Cap,rotor, and wires,...Does It shortly after cold startup, and after sittin for for a short time,...then It runs like a raped ape,...I'm feelin like Its an AIS or TPS issue,...anyone else have this prob,...
 
mine did the same thing (96 XJ 4.0 HO). i took the throttle body off and completely apart, soaked it , and put it back together with a very thin layer of high temp permatex. problem solved. when unplugging any sensor , you have to reset the computer. you do this by taking the positive side of the battery cable off and ground it to the body for at least 10 -30 seconds. this will discharge the capacitors in the computer.you can also get carbon built up in the TPS make sure it is clean and working freely...hope this helps
 
almost sounds like a TPS sensor or coolant temprature sensor, have you checked the coolant temprature sensor?
 
73AbodEE said:
mine did the same thing (96 XJ 4.0 HO). i took the throttle body off and completely apart, soaked it , and put it back together with a very thin layer of high temp permatex. problem solved. when unplugging any sensor , you have to reset the computer. you do this by taking the positive side of the battery cable off and ground it to the body for at least 10 -30 seconds. this will discharge the capacitors in the computer.you can also get carbon built up in the TPS make sure it is clean and working freely...hope this helps
Click to expand...

Headed back out to the barn to poke at it some more,....I've seen dirty throttle bodies (horizontally mounted) cause stalling at stop lights before...
 
I FINALLY FOUND THE PROB,...Front O2 sensor,...after weeks of checking and rechecking, removed and cleaned the Thottle Body, New plugs, hours of running around with a scan tool attached, I called my buddy Tony @ Westbrook Auto,...as it turns out he had a 4.0 Wrangler with the same exact problem. Drove him and his crew nuts. Happiness, Joy and Rapture. New O2 installed and my Cherokee is much happier.
 
I don't understand why a problem like that didn't show up in a code scan.
 
Only thing i can figure is the front O2 has a leetle teeeny tiny dead spot betwixt closed and open loop, just not long enough to register a code.
 
Yes o2 sensors are a common problem for this. The heater cucuit leaks power into the control side and the computer sees a rich condition and commands a lean mixture. Once the o2 gets hot enough it works alright. This can also be caused by a lazy o2 that doesn't start controling right away- same results though.

Garth
 
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