Po 300 misfire

Discussion in 'KJ General Discussion' started by Cooker69, Sep 20, 2020.

  1. Cooker69

    Cooker69 New Member

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    Having po 300 misfire code. Also had po 306 as well. Replaced #6 coil pack. Still getting po 300. Seems to run good but gets a little shaky at idle. I replaced all spark plugs. Noticed today a bit of white smoke at start up then went away? O2 sensor perhaps or a possible head gasket going? Any advice , comments or suggestions would be greatly appreciated, Dean.
     
  2. Cooker69

    Cooker69 New Member

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    Forgot to mention that its a 05 liberty with the 3.7
     
  3. tommudd

    tommudd Moderator Staff Member Moderator

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    What plugs did you use NGK coppers I hope
    Have you swapped the coils around to see if it moves with them and why just change number 6 ?
    does it hesitate any starting up a grade ?
    Have you done a pressure check yet on all cylinders ?
    Checking compression is way to easy,pull all the spark plugs,remove ASD relay,screw in a compression tester(found at most auto parts places ),crank the engine for 2-3 seconds,then read what that cylinder is reading and do the same for all 6 cylinders.Do this test once cold(all cylinders) then do another when the engine is warm.The cold cylinder psi should be 170-225psi for your 3.7 with no more then about 25% difference between the cylinders,warm test should be closer to the max spec then the cold test.
     
  4. Cooker69

    Cooker69 New Member

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    Thanks for the reply tommud. I just moved #6 to #1 cylinder that was it. Still getting random misfire. I was getting #6 before and now in 1 position it seems to be fine so old coil should be good? It actually seems to have lots of power up a hill. Rough idle on idle but smooths right out on acceleration. I have not done compression checks or cylinder checks yet.
     
  5. Cooker69

    Cooker69 New Member

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    I couldn't get ngk so I had to buy champion plugs. Are they garbage? These were the old plugs
     

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