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Thread: Cylinder 1 misfire

  1. #1
    Fresh Catch capncc's Avatar
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    Cylinder 1 misfire

    2011 Rubicon
    2.5 inch lift
    35x12.50 NITTO ridge grapplers
    5:13 gears
    97500 miles
    Superchips 91 octane tune

    I was accelerating rating up the local toll road hill and she started shutting down , engine light comes on. Nurse it on home and DTC is PO301- cylinder 1 misfire. Replaced plugs, wires and coil pack cleared he code and test drove no problems. Drove to to next day itís ok, heading home got on the same toll road accelerating up the hill she shuts down again same code and now itís knocking and misfiring all the time. Time to get a compression check. Anyone have this problem?

  2. #2
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    Injector issue?

    Do a compression and a leakdown test, but if you replaced all the ignition parts, I'd look at injectors next.

    Also, possibly look at the ignition wiring, trace it back along with the injector wiring. Look for damage.

  3. #3
    Hooked Noble Woodsman's Avatar
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    I haven't had this issue with a jk yet, but there are a few things you can try if the compression looks okay...

    Check vacuum pressure

    Check fuel pressure

    Swap the new coil, spark plug, and spark plug wire with another cylinder, reset codes and check if misfire moves to the new cylinder

    Swap fuel injector with another cylinder and see if misfire moves

    Replace Camshaft position sensor. I would try this last, because it's less likely and it's more of a part swapping approach instead of troubleshooting.

    It may be a good idea to return the programming to stock first. I'm not sure if the 91 octane program would complicate the search.


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  4. #4
    Addict jeeeep's Avatar
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    i'd check the easy stuff 1st - plug, wire, spark from the coil pack

  5. #5
    Fresh Catch capncc's Avatar
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    Thanks for the feedback.


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  6. #6
    Guy with a Red 2-Door cozdude's Avatar
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    Quote Originally Posted by capncc View Post
    2011 Rubicon
    2.5 inch lift
    35x12.50 NITTO ridge grapplers
    5:13 gears
    97500 miles
    Superchips 91 octane tune

    I was accelerating rating up the local toll road hill and she started shutting down , engine light comes on. Nurse it on home and DTC is PO301- cylinder 1 misfire. Replaced plugs, wires and coil pack cleared he code and test drove no problems. Drove to to next day itís ok, heading home got on the same toll road accelerating up the hill she shuts down again same code and now itís knocking and misfiring all the time. Time to get a compression check. Anyone have this problem?
    Easiest thing to do would be to move the plug and wire to 2 different cylinders. If the misfire follows either one of those then thatís your issue. If it stays at cyl 1 then itís going to be an injector issue.

    Do you have any other codes popping up as well?
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  7. #7
    Fresh Catch capncc's Avatar
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    No other codes

  8. #8
    Fresh Catch capncc's Avatar
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    Compression test results

    I did the compression test and here it is:
    Cylinders 1,3,4,5 and 6 are 185 psi
    Cylinder 2 was 30 psi and the plug electrode-had oil on it
    Iím not sure why the code was PO301

  9. #9
    Hooked Noble Woodsman's Avatar
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    Quote Originally Posted by capncc View Post
    I did the compression test and here it is:
    Cylinders 1,3,4,5 and 6 are 185 psi
    Cylinder 2 was 30 psi and the plug electrode-had oil on it
    Iím not sure why the code was PO301
    Wow. Any idea why compression is bad on cylinder 2 only?


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  10. #10
    Nothing but a Thing Snboarder113's Avatar
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    30 psi isnít really enough to run. You sure you got a good seal on the hose?
    If itís actually at 30 you shouldíve had a hell of a lot more codes.


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