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One spark plug fouling over time

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I have a 1995 K1500 W/T with the 4.3 V6 and 5-spd. About a year ago it started hesitating during low-speed acceleration. I changed the plugs and wires, and one of the plugs was covered in gray/tan crusty ash, enough to ground the electrode. All the other plugs were fine. Now, a year later, the same problem is happening with the same plug. I replaced the plug again and it's better, but I pulled it out again last night and it was starting to collect crud again.


The Haynes manual says it's likely due to valve guide seals, but I don't use any more oil than I ever did (<1 qt between changes) and it doesn't smoke at startup. It's only this plug, all the others are perfect.


Any ideas? I was thinking fuel injectors, but it's TBI, so wouldn't that affect other cylinders too?


Thanks in advance.

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How is the sparkplug wire going to that plug? Maybe the wire is bad causing the plug to miss-fire at times.





Well, I replaced the wires after the first time the plug fouled, and it didn't seem to help. Does seem ignition related though. I also replaced the cap and rotor last year too...

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  • 2 months later...
  • 2 weeks later...

oil fouled plugs are usually black so that doesn't sound like the problem.


TBI has 2 injectors, it is kind of a Y system that feeds 2 outside cyl's on one head and 1 middle cyl on other head with fuel. generaaly if injector problem on TBI you lose 3 cycls on the V6. so that aint the problem either.


that leaves you with ignition problem on one particular cylinder or vacuum/compression leak at the offending cylinder.


did it actually foul the plug this time or it was just ash coated?


maybe you can try a hotter plug on that cylinder

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