P0308 Misfire? Could've been a valve cover oil leak.

Discussion in '2nd Gen DIY' started by bluwarguy, Feb 15, 2017.

  1. bluwarguy

    bluwarguy Member

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    So, ever since december my truck began to misfire. Specifically the 8th cylinder. Looking at a bunch of things online, I arrived to the conclusion that it must be the plenum. Boy was I wrong.

    While I was saving up money to get a plenum repair kit, I decided it was about time to change my spark plugs and finally fix the valve cover gasket leaks that were going on. Well, upon removing the 8th cylinder spark plug, this is what I found:
    [​IMG]

    It's entirely caked in oil. No wonder it was misfiring!

    So, after replacing it with Champions, it ran just like the day I bought it.
    The moral of the story is to always keep your valve covers from leaking.
     
  2. MCIntoDarkness

    MCIntoDarkness Member

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    This has got me thinking that this might be the cause of my misfire on cylinder 6 on my 3.9L. I always get it if I push the truck about 70-75mph. :roflsquared:
     
  3. bluwarguy

    bluwarguy Member

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    mine was always around 45mph and above

    turning overdrive off helped it stop, but I figured out the permanent solution thank god
     
  4. dodge dude94

    dodge dude94 Senior Member

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    A leaky valve cover won't cause that fouling, that's a bad plug or excessive oil dump from the valves.
     
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  5. dapepper9

    dapepper9 Senior Member

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    ^^^valve cover leak can't get into the cylinders
     
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  6. Gr8bawana

    Gr8bawana Senior Member

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    If it was a valve cover leak there would be nasty oil residue all over the outside of the plug. Oil can't seep into the cylinder.
     
  7. dudeman2009

    dudeman2009 Senior Member

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    If it did, you have worse problems than a miss at certain speeds :roflsquared:
     
  8. Yeret

    Yeret The Village Drunk

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    Wow, that is probably the worst fouling that I've ever seen on a spark plug. Even when my plenum was leaking, my #8 plug wouldn't foul that bad.

    Pepper's right. Leaky valve covers at worst will coat the outside of the spark plug, but a leak there won't find it's way into the cylinders unless maybe the intake manifold gaskets are also toast.

    If you're using oil, knowing that it's a Magnum engine, I'd plan on doing the plenum repair. If money's tight, people have had success with simply using a revised Fel-Pro plenum gasket for 20 odd bucks rather than shelling out the 160 for the kit.
     
  9. Shadow_Death

    Shadow_Death Senior Member

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    Plenum plate would be my guess as well. I recently bought a 96 off my niece which I know needs the fix. No vacuum, misfire on #8, oil consumption and leak down the back of the block, as well as if I let it idle long enough the miss gets slightly worse.
     

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