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  #13  
Old 04-16-2014, 07:27 PM
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You said it happens after 50mph. So I am assuming the engine is warmed up and the issue presents itself on a warm engine versus a cold one.
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Old 04-16-2014, 07:29 PM
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Re: P0300, P0301, P0306 codes

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Does it blow smoke at all whether its blue or white?
No it does not even when I got the system cleaned out.
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Old 04-16-2014, 07:33 PM
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Originally Posted by vlilley74 View Post

No it does not even when I got the system cleaned out.
I see. That rules out a few things. Have you checked you vacuum lines? Maybe one is dry rotted or split.
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Old 04-16-2014, 07:34 PM
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Re: P0300, P0301, P0306 codes

I have been checking those as well
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Old 04-17-2014, 02:18 AM
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Re: P0300, P0301, P0306 codes

There is a TSB regarding multiple cylinder misfires due to sticking valves. The valves can stick due to carbon buildup on the valve stems. Can not attach anything now, but have a look at the TSB's at WJJeeps.com - Jeep Grand Cherokee WJ 1999-2004.
They use some mopar cleaner, but seafoam or alike could help.
If that doesn't help, i would swap the injectors from cylinders 1 and 6 with an other position and see if the misfire follows. Worst case could be the PCM.
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Old 04-17-2014, 04:50 AM
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Re: P0300, P0301, P0306 codes

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You said it happens after 50mph. So I am assuming the engine is warmed up and the issue presents itself on a warm engine versus a cold one.
yes your assumption is correct
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Old 11-27-2014, 07:48 AM
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Re: P0300, P0301, P0306 codes

I am having this same issue on my '04 4.0. I am getting the misfire in cylinder #1. Changed plugs, injectors, and coil pack. At 45-50 mph when I touch the gas it acts up, can feel the misfire. Running out of other things to try short of taking it to a shop. Any ideas?
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Old 11-27-2014, 07:53 AM
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Re: P0300, P0301, P0306 codes

Welcome to the garage.
Did you already try a seafoam treatment? Sticking valves due to carbon buildup can be your problem.
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  #21  
Old 12-10-2014, 09:40 AM
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Re: P0300, P0301, P0306 codes

I fought this same war all summer. Had a professional mechanic working on it with me. Tried EVERYTHING...no dice. Even tried a new ECU. My problem ended up being the valvetrain. I had the head sent to a machine shop and gone over and not a single problem since. My symptoms were identical to yours. I went over ignition, fuel injection, ECU, spark plugs, coil, etc. etc. etc. even had compression checked, etc. Nothing solved the issue so I finally pulled the head and BINGO the valves needed work.

Good luck.
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