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Old 06-19-2016, 06:06 PM
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4.0 jerking proble

My girlfriends 2003 wj 4.0 has been jerking during acceleration right after launch, occasionally at idle, and cruse. She had the codes pulled and they poited at the #5 spark plug saying it has been fouled and a bad IAT sensor (I had recently replaced the sensor about 3 months ago).


After that her father bought her 6 new plugs and I installed them all at the same time with a gap of .035.

I drove it and noticed no issues with acceleration and no jerking. After that I took it back to autozone to get the codes pulled again and just as I expected the IAT sensor code was thrown once again. I got a new sensor and got my money back from the old one as I was hoping it was faulty. Afterwards I replaced the old sensor and the jerking proplem resumed during acceleration. At which point it was taken back to autozone and now the code for low power to the IAT sensor has been thrown.

I know I can get a pigtail from a junk yard which I will do soon but I wanna know if anyone has had this particular problem before. Can low imput from the IAT sensor cause this jerking or does the coul packs need to be replaced? Should the ignition rail be replaced all together? This is the 3rd set of pluds in this 187,000 mile jeep. My girlfriend's father told her that the ignition rail is the same one from the factory and the coil packs were last replaced long ago however they do still look great.

Any imput would be much appreciated and thanks for reading.

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  #2  
Old 06-20-2016, 07:05 AM
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Re: 4.0 jerking proble

Can you give the exact fault code(s)?
I would not expect the coil pack yet, as it doesn´t show a misfire now.
A wrong inlet temperature input will mess with the calculations for the injector pulse, so could be the problem. I would measure the wires from the IAT sensor to the PCM. Check for continuity while wiggling the wires. If ok, check both wires for short to ground, also while wiggling the wires.
Also check the PCM connector pins for moisture and/or corrosion.
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Old 06-20-2016, 07:30 PM
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Re: 4.0 jerking proble

Thanks for the input, I'll check those wires and connectioms promptly. I belive the code was a P0112 if my memory serves correctly? I'll pull the code again in about an hour and tell ya for sure.
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Old 06-26-2016, 06:19 PM
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Re: 4.0 jerking proble

Sorry i didnt get that code to you but i did check the wires and one of the wires to the IAT sensor got smashed which I expect is the problem, it will be replaced soon.
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Old 06-29-2016, 03:17 PM
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Re: 4.0 jerking proble

I changed the wires that were crimped and there were a few that were nicked too but the jeep is still jerking. I guess its onto the pigtail now.

Any thoughts?
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Old 07-06-2016, 09:14 PM
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Re: 4.0 jerking proble

I haven't yet replaced the pigtail to the IAT sensor but I think that isn't the cause of the excessive jerking. I belive it's the transmission slipping and badly too. It slips in all gears and when I checked the fluid it was at the bottom of the dipstick. I made sure it was at operating temp by driving it for a few miles, and followed the steps i found on a forum, setting it on a level surface, putting the parking break on, shifting the transmission from park, reverse, nuetral, drive, and, and 1st, then back to nuetral. Turns out the fluid was about a quart and a quater low. I added a quart of oil with no resolve to the slipping.

Any more help would be greatly appreciated.
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Old 07-07-2016, 11:48 PM
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Re: 4.0 jerking proble

Are you sure that the transmission is slipping and that it is not the torque converter?
If it really slips in all gears, then it could be due to a too low line pressure. Only by measuring this pressure you will know more.
If the transmission really slips, then you need to be carefull to not burn the clutches. How does the fluid color look like and how does it smell? Black fluid or a burning smell to it is a sign of burned clutch(es)/bands.
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