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avanti plug fouling

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  • avanti plug fouling

    My R2# 1 plug fouls frequently.When removed it's all black& sooty.
    The threads on block have oil on them as well.Top of piston is
    also foul looking.the area below the plug [ while installed]
    is oil soaked. Could oil be forced out the plug threads to cause
    this? The car doe's run strong,however.Thanks JNP


  • #2
    How are your valve seals? that would be my first suspect, and while you have the valve covers off check your oil return passages.

    good luck,


    55 Commander Starlight
    55 Commander Starlight


    • #3
      First of all, oil isn't being forced out past the plug threads. If the plug is that loose, you'd hear compression popping past it when the engine's running. Oil on the outside is usually valve cover gaskets leaking. You say the plug is black and sooty. If it's dry soot, that too rich of a fuel mixture, if it's oily or crunchy, it's oil.

      A good way to figure out what's going on is to get the car warmed up and put a clean or new plug into that cylinder and take it for a drive. Take the plug out and see how it looks. See if it's black and dry (rub your finger across it), black and wet or just fine. If it's ok, put a clean plug in and later start the car up cold. Run it for a few minutes and pull the plug. Black and wetness that dries is fuel, black and oily is oil.

      It'd be pretty hard for one cylinder alone to be running too rich and the rest be ok. If one side of the carb is screwed up, the four cylinders fed by that side would be over fueled but not just one. If it's actually dry soot on the plug and it is being over fueled, is there a vacuum/pressure line plumbed into the intake manifold near that cylinder? I believe the supercharged engines used boost pressure to assist the fuel pump. I don't know where that line gets it pressure from, but is it plumbed into the manifold any where close to #1? If the fuel pump diaphram is leaking, engine vacuum could be sucking fuel from the fuel pump through that line.

      If the plug is oily and the car runs good, it's probably the valce setm seal as nate said.


      • #4
        Most likely, it is a valve stem seal, scored cylinder wall, broken ring or other mechanical problem causing oil to be admitted into that cylinder. However, do the following checks:

        1. Put a new spark plug in the #1 cylinder and pull each plug wire in turn and note the RPM and vacuum drop. Do all eight cause the same drop? If #1 does not drop the RPM/vacuum at all, check the following
        2. It is possible for a distributor cap to have a carbon track down from just one terminal. Try a new cap
        2. Bad plug wire. Try a new wire
        3. Sticking valve. Do a compression check of all eight cylinders. They should be within 10# of each other
        4. Intake gaskets. Squirt oil around each intake port. If it is leaking, the oil will be sucked in and smoke will come out the exhaust. You can use an unlit propane torch. The engine will speed up if propane is being sucked in. On a supposedly pro-rebuilt engine, I found two intake leaks.
        5. Exhaust heat riser valve stuck closed. Even though this affects four cylinders, a weak cylinder will be affected more.
        6. Plugged PCV valve or plugged oil drains in the head. Again all cylinders would be affected, but a bad cylinder or missing valve stem seal is affected more.

        thnx, jv.



        • #5
          Thanks much guys!Ill'explore afer the holidays.

          63R2AVANTI JOHN