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Oil in plugs and lot of misfires

Discussion in 'Gen 2 Prius Technical Discussion' started by Alexano, May 31, 2019.

  1. Alexano

    Alexano Junior Member

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    From last some months I am experiencing lot of missfires on cylinder 4 and low performance of engine on my Prius 2007 model. In morning there is lot of voice and vibration from engine and after sometime it runs smooth but still performance is low.

    I checked plug of cylinder 4 and found that there is oil on it please see attached image of that plug. I suppose that in morning due to oil in plug one cylinder does not work that's why is lot of vibration.

    I searched on internet and found at it may be due to valve cover gasket and if I will change that gasket its performance will be better and there will be no oil in plugs. What do you recommend will it solved that problem or I will need to replace my engine or there is any other solution?
     

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  2. jb in NE

    jb in NE Senior Member

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    If you are having a misfire on this cylinder (as determined how?), then I would swap the coils on cylinders 3 and 4 and see if the misfire moves to cylinder 3.

    The oil on the outside of the plug indicates an oil leak on the seal around the plug on the valve cover, but should not be causing the misfire.

    Plus - that plug looks pretty old. I would also put a new set of plugs in.
     
  3. Alexano

    Alexano Junior Member

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    There is misfire codes on techstream scanner for cylinder 4. I already swapped coils but still codes are for cylinder 4.

    I also replaced fuel injector but still same thing. Also those plugs are just 4 month old and remaining 3 plugs are in good condition. Only 4th coil is in bad condition. I replaced that coil but still misfire on same cylinder.

    What can be its cause?
     
  4. jb in NE

    jb in NE Senior Member

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    Given that you have checked the coil, I would start moving up the path to the source of the coil signal and ensure the coil is being fired.
     
  5. 69shovlhed

    69shovlhed Surly tree hugger

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    I don't see any oil on the outside of the plug. if there is oil in the combustion chamber, you either have gummed rings, failed rings or bad valve seals. if the oil is on the outside and I just don't see it, then yes, reseal the valve cover and swap the plugs from 3 and 4 to verify its not just a bad spark plug. I have seen spark plugs defective right out of the box.
     
  6. Alexano

    Alexano Junior Member

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    I have tried to replace coil but still same problem.

    Note: it runs smooth when car warms up but in morning engine gives too much noice and viberation until i accelerate for atleast 10 seconds. Also outside temperature is normal in morning like 32 degree. Also i get misfire code just in morning.

    Can it be due to some electric issue like wire connected with coil?
     
  7. jb in NE

    jb in NE Senior Member

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    It could be. Intermittent issues can be tough to diagnose. If you can swap components along the way (with a known good cylinder), that can sometimes speed things up. When the problem moves to another cylinder, you have isolated the component.