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My Festiva is running a little rough (black spark plug)

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  • My Festiva is running a little rough (black spark plug)

    My 91 fuel injected has been running rough for a few months. Mostly dipping RPMs at idle and during coasting I bit of roughness as well. Never stalls, just a bit rough.

    Pulled the spark plugs and the tip was completely gone on cyl # 3. It was basically disintegrated. I think I heard it happen too.

    Put in all new plugs and new wires. No improvement. Checked the #3 plug after a week and it was already black. The others looked fine.

    I am thinking too much fuel since it's black so soon... maybe a leaky injector? Is that common?

    Any other ideas?

    Thanks!

  • #2
    Could be a burnt valve on that cylinder, can you do a compression test?
    ~Nate

    the keeper of a wonderful lil car, Skeeter.

    Current cars:
    91L "Skeeter" 170k, Aspire brakes, G15, BP, Advancedynamics coil overs, etc. My first love.
    1990 Kawasaki Ninja 250 - my gas saver, 60+mpg - 40k
    2004 MotoGuzzi Breva - my "longer range" bike - 17k

    FOTY 2008 winner!

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    • #3
      Originally posted by skeeters_keeper View Post
      Could be a burnt valve on that cylinder, can you do a compression test?
      Yeah, I have been meaning to do one. Thanks

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      • #4
        You could also remove the valve cover and look around. A leaking exhaust valve will leave black depostis on the underside of the valve cover right above the valve. On mine it was carbon deposits keeping the valve from closing and I was able to use a chemical cleaner to fix it. However black depostis on the spark plug would be incomplete combustion from too much oil or gas in the combustion chamber? I guess the other thing could be timing. I find a cheap vacuum guage or a tachometer shows misses by vibrating.

        PS this sort of question goes in the repair help forum where it's likely to get more respnses.
        Original owner of silver grey carburetted 1989 Festiva. 105k km as of June 2006.

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