Spark Plug Diagnosis? (Removed After Misfire)

jaymar

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I think its not terrible, but not great.

I agree it looks a bit sooty / carbonised.

Also think it could be a bit of oil being burnt. Are you losing oil? Or seeing any blue smoke in the exhaust.

How many miles on your engine?

Mine was burning oil, and ready for valve stern seals at 200k km (130ish miles)

If it's burning oil, the sooty residue on the plug might have an oily consistency if you rub it
Yeah I'm losing oil, but that is--so far as I know--only b/c of front main seal leak. Will check to see if residue oily.
 

jaymar

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You talking about the stain on the top part? (Upside down).

I was wondering about that too. What's that? Leaking compression through the body of the plug?
Same misfire issue with new plug, so either that's happening with both (could be; same batch, but no misfires on other cylinders), or it's a different issue, or there's an overpressure forcing a leak? Is that possible?
 
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Same misfire issue with new plug, so either that's happening with both (could be; same batch, but no misfires on other cylinders), or it's a different issue, or there's an overpressure forcing a leak? Is that possible?

Have you done a compression test?

I'd be checking
- plug lead is not damaged
- distributor cap and rotor aren't damaged
- injector at that cylinder is working,
- injector harness is in good condition. No damage and no broken clips at the injector
- check for coolant in oil,
- check for combustion gas in coolant
-
 

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