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Old 12-03-2011, 09:54 AM   #1
Join Date: Dec 2011
Location: Falcon, CO
Posts: 2
2002 Wrangler Misfire problem solved!!!!!!

All, there have been varying degrees of success solving the misfire problem from what I can see. Here are my notes on how we solved in my Wrangler.

I have 2002 Wrangler Sport 4.0 stock engine with 141,000 miles.

Here Is what I gave my mechanic when I gave up throwing random parts at the problem.

  • Oil Guage has been reading high pressure – I felt Sending unit bad – It has been that way for 90 days or so. Problem is intermittent
  • Check engine light came on a couple times, but did not flash did not stay on
  • Jeep has been running fine
  • A year ago, I had the engine very hot climbing a pass, with low coolant. Got into red, but did not peg the temp guage

Misfire Information
  • Drove the Jeep about 30 miles, ran fine stopped at the store and restarted
  • restart, it started running really rough, I do not recall any noises
  • Started driving and as I accelerated Engine cuts out, low RPM fine, Flashing check engine light comes on
  • Stop, listen, look, no evidence of any problems, idle a bit rough, still around 800 rpm
  • Start driving, still cutting out and flashing check engine. The problem occurs at about 2800 RPMs, engine cuts out. Low RPM’s things run ok, still rough
  • Codes are P0306 and P0303 – I believe misfire on cylinders 3 and 6
  • After internet research, replace Cam Position Sensor, disconnect battery to clear codes run again. Runs fine for 10 min, still a little rough. After 10 min, flashing check engine light and 2800 RPM cutout comes back
  • Code P0303 this time
  • More research, replace spark plugs. Old plugs were very worn, installed Bosch Platinum gapped to .035. Cleared codes by pulling battery cable
  • Start run, a little rough, but accelerating fine. After 10 of driving 2800 rpm problem returns. Code P0303 back.
  • At this point I’m convinced #3 cylinder has some issue
  • Concede to experts
  • Drove the Jeep to the store in very cold temps. Ran rougher than before and got a new code P0135 02 Sensor error, P0300, P0304, P0303, P0305, P0306
  • also noted at idle exaust seems to have a strong puff and chugging noise.
  • Now we are going to the mechanic

What the Mechanic did -- $822 in the end
  • Clean Fuel Injection system
  • Computer Flow Chart/Repair - Cylinders look fine, O2 Sensor heater circuit is no good.
  • Seafoam Clean done
  • p0303 still there
  • compression good on #3 cylinder
  • some sort of carbon test was done with #3 fuel injector disconnected. When connected, readings bad, clean when disconnected. This told mechanic likely spark problem.
  • replaced coil rail and all problems disappeared.
  • He also tighted the valve cover gasket to fix leak, but that was unrelated.

I've only driven about 50 miles of far, but no sign of any problem and the Jeep is running way stronger than it has in a couple months.

It was expensive, but I talked to the mechanic and agreed to all work, based on his opinion and what I saw in my own internet research. Hopefully, this will help you lower total cost to fix

One More Note: Mechanic referred to Chrysler Service Bulletin 09-003-03 dated Aug 1, 2003. The recommended approach looked like a valve job without really getting one. It was a disassemble and clean job on the lifters. My mechanic suggested we try Seafoam, before going to the extent of this bulletin. Thankfully, that would have been hours and lots of $$$$$$

Follow me, I'll be right behind you
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Old 12-03-2011, 10:04 AM   #2
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Join Date: Jan 2011
Location: Cape may NJ
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i just got mine fixed.. they charged me 200$ for 4 spark plugs.

I brought it in strictly for a diagnostic so i could fix it and they went ahead and did it.

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Old 06-06-2013, 07:53 PM   #3
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Join Date: Apr 2013
Posts: 2
Ive done everything you did but went farther. Eventually I replaced the fuel pump and found both filters clogged almost completely. Run almost 3 tanks of gas through it in all road conditions, even some extreme angles at a local clay pit and I haven't had one problem..... yet
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Old 06-06-2013, 07:57 PM   #4
Knows a couple things...

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Originally Posted by Achilles-tj View Post
Ive done everything you did but went farther. Eventually I replaced the fuel pump and found both filters clogged almost completely.
Exactly how did you determine both filters were clogged? How did you determine the primary filter was clogged? Do you live outside of the U.S.?
When you have a choice, buy American.

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Old 06-06-2013, 08:36 PM   #5
Join Date: May 2013
Posts: 35
Thanks so much for posting this... I am experiencing some of the very same problems you outline above... Today I noticed that at idle the motor seem to run a little rougher than I noticed before. THen on the way home from work the engine light came on but seem to be running fine at speed. I looked over the gauges and noticed the oil pressure gauge was running a little higher than normal (almost halfway between the center dot and the next dot). I haven't pulled the codes yet but was initially thinking a coil issue as well. My jeep has 87k on it... I will post more later...
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