Diagnosing Misfire code, advice?

Discussion in 'Renegade Stock Tech' started by Murf, Jan 14, 2020.

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  1. Murf

    Murf New Member

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    I have a 2017 Latitude with 2.4 engine.

    In June 2019 at 50K miles I replaced the spark plugs with "NGK (5018) LFR5AGP" (Platinum plugs).

    In November 2019 while driving on a trip I experience rough engine at 70MPH and then after awhile Service Engine light came on. Went to AutoZone and they pulled a "P0301 Cylinder #1 Misfire" code.
    I pulled the boots off all 4 plugs and added ample amount of dielectric grease (I didn't put much on before). When I started it back up and the Service Engine light and message disappeared all on its own to my amazement. No problems on trip home.

    Everything has been fine until this weekend. While setting in a drive thru I thought I notice the engine did a little rough idle for a brief couple seconds and that was it.
    The next day I went somewhere. When I came back out and started the Jeep the Sevice engine light came on. I pulled the code when I got home and it is the "P0303 Cylinder #3 Misfire" . The engine seems to be running without misfiring as far as I can tell by the feel and sound.

    I now have 62K miles on the Jeep. Can a different plug than the OEM be detected my the "computer"? Is it all that particular about plug brand/type? After all, isn't all that matters is there is a spark.

    I'm trying to think what it could be since it switched cylinders and the plugs is the only thing I can come up with.

    How do I diagnose this. Starting with the simplest things first.

    Thanks for your help,
     
  2. IDoMy0wnRacing

    IDoMy0wnRacing Well-Known Member

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    Dielectric grease. A dab, something the size of a tic-tac is recommended. don't put tooo much.

    Trouble code for the P0303. Swap the coil with the code, cylinder 3 with a coil from a different cylinder, cylinder 2 for example to see if the DTC move to cylinder 2. Drive it around for a while and recheck for codes. If the faults shows up at cylinder 2, the coil is at fault. Replace the coil.
    If the code comes back to cylinder 3, the plug is at fault.

    It sounds like one of your coils is failing. Not uncommon with our 2.4l engines.

    NGK is a very good plug for our 2.4l.
    AVOID Autolight. Autolight has never worked well in Chrysler vehicles.
     
  3. Murf

    Murf New Member

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    Thanks. Good idea on the coil swap. I had the error on cylinder 1 in November. Now it is on cylinder 3. I only felt it briefly and that was all on Cylinder 3. I got to looking on the internet and found this video:
    I didn't realize all the trouble a bad PCV valve can cause. So I ordered a new one and will see if that helps. I believe I still have the original PCV valve with 62K on it - never been changed.
     
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  4. Murf

    Murf New Member

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    So after the PCV valve replacement, I got another P303 error / misfire on clyinder 3. So I swapped coil packs on cylinder 3 and 4. I'm still getting misfires on cylinder 3. Does that mean it is the spark plug? They are NGK platinum and only have 13K miles on them. Can plugs go bad that quick? Is that the next thing to try, buy a new spark plug for Cylinder 3?

    Thanks
     
  5. IDoMy0wnRacing

    IDoMy0wnRacing Well-Known Member

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    I have seen a single plug fail, but I haven't seen it with NGK. NGK's are good plugs.

    Tip: when troubleshooting a misfire. Try moving the component to a cylinder that isn't next to the one in the firing order.

    1-3-4-2 firing order. so move 3 to 2 so to speak.
     
  6. Murf

    Murf New Member

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    Ok, I'll move it to 2. I'm thinking it is the plug because the first time it happened it was back in October and on Cylinder 1. It hasn't happened on cylinder 1 again. Consistently on 3 since then. The NGK are Platinum .047 gap. I'm thinking I'll try the Denso iridian .044 gap and replace them all. Maybe they had a bad run at the plug factory. Thanks
     
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  7. Murf

    Murf New Member

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    I noticed the plugs I originally took out where Champion, not Mopar. Maybe they weren't originals. They were a little longer than the NGKs I took out today. I replaced them today with Denso. Well I know why the cylinder 3 was mis firing. The electrode is completely gone and the "L" thing that goes under it half way gone! See picture. Hopefully the Densos do better.
     

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  8. IDoMy0wnRacing

    IDoMy0wnRacing Well-Known Member

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    That would definitely cause a miss.

    Longer plugs are usually an indicator of a cooler running plug (referring to the insulator end that melted off).

    MOPAR doesn't make spark plugs, OEM are Champion plugs.

    NGK is a good plug, makes me wonder why???

    DENSO is a good plug also.
     
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