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Have an 02' jeep liberty with a 3.7l v6. Originally received a random misfire code and a code for misfire on cylinder 5. Replaced the coil on cylinder 5 and the random misfire code and misfire for cylinder 5 went away but started receiving a code for misfire on cylinder 6??? Switched a known good coil with the coil that was on cylinder number 6, cleared codes, drove around, code stayed consistent. Removed the fuel rail and injectors, tested and cleaned each fuel injector, reinstalled, cleared codes, went for another test drive, same code cylinder 6.

This thing is running so poorly I find it hard to believe it could just be a single cylinder misfire. After it sits for a bit and you clear the codes you can take it down the road and it will be (barely) drive-able. After about a mile of 60mph up some hills the check engine light will come back on. At this point the vehicle begins to buck, almost like it's trying to die, then picks itself back up. It will do this until you take release the accelerator and let the transmission shift all the way down.

Even after this behavior the only trouble code is P0306 for cylinder 6 misfire. Took a gamble and replaced the camshaft position sensor. Cleared the codes, went for a drive, and the same behavior persists.

What else could be causing this behavior? Ignition control module/Transistor pack (if these engines have one of those)? Open to any suggestions.

  • I assume the filters and spark plugs got checked? – Martin Aug 21 '16 at 18:56
  • Plugs yes. Is there a fuel filter that is serviceable (not in tank)? – nullReference Aug 21 '16 at 19:17
  • How are the spark plugs? – Zaid Aug 21 '16 at 21:07
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From interpreting the question and the comment I would recommend the following:

  1. Change both fuel and air filter. I don't exactly where the fuel filter should be in your vehicle. Normally it is near the tank, jack the vehicle up and follow the fuel line from the engine back to the tank. If changing the fuel-filter is problematic: Start by changing the air-filter and testdrive the car.

  2. If the problem persists: Check the pump/eventual filter in the tank. I have only changed a fuel pump once at a small european car, so I wont be a big help here. Just in case I write how it was done: It was necessary to pump out the fuel with an external pump, open the fuel tank hatch located under the rear seats, open the tank by rotating the circular seal/opening and replace the in-tank module.

Are there any sounds / other observations of something that seems not to be right?

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