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Read my plug

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What would cause this?


In case you can't see it well in the pics, it looks like a well used wire feed welding tip. I know the huge crack doesn't show at all on it. Lastly, the ground, instead of curving over, just kind of leans inward.


The plug is my #2 cylinder plug and has bout 3000 miles on it. #1, 3 and 4 all show a lean condition. This is my brand new motor that started rod knocking in the third cylinder so I pulled it to have it re-rebuilt.

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That looks to be running RICH, really, really RICH.


The only other time I saw a plug looking anywhere close to that was a race motor that overheated, and it was experiencing uncontrolled combustion.

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my guess is its getting very hot in that cyl. only guess with TBI would be that the cyl isnt being lubricated completely, making extra heat, explosions are stronger, and melted the ground?


I'm probably way wrong, but it's an idea, a possibility. Seems logical, but out there.



Pull the head, and check what the cyl walls and the head looks like. also, maybe an ignition problem, for some reason getting stronger sparks, acting like a plasma cutter?

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I don't know much about spark plugs, but it looks like you had some nasty pre-ignition or perhaps FOD, which obliderated the plug and then it was followed by carbon fouling as that cylinder wouldn't run worth $#!& (probably didn't even fire half the time). The lean condition on the other plugs is possibly related because a cylinder not firing messes with the O2 sensor readings.



While it doesn't matter as much on water cooled engines, any chance the plug was dropped/smacked before install? If you break the insulator they don't shed heat correctly and can cook themselves... It's more apparent in an air cooled engine.

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K, what I think it might be is:

Motor was running lean.

Vacuum leak on the motor faulted the timing.

Cracked plug couldn't cool.

Cracked plug burnt up.

Other cylinders stayed lean.

Cylinder 2 couldn't fire many, if any, times.

Extra fuel in cylinder makes plug show rich.


That's kind of what I gathered from what everyone says and put together as pretty logical.

I can't try another plug right now because the motor's out of the truck to be rebuilt, again, but I'll make sure that the new set of plugs don't get dropped. The old ones might've; it happens.


Thank you, guys!

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