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Oil Fouled Plug How to Troubleshoot

alohamonte

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Looking for the procedure to troubleshoot an oil fouled spark plug. I believe it's #4 plug (drivers side front, closest to the radiator).

I found this when changing all plugs today as part of a tuneup. The others all had a bit of dry carbon on the threads.

No CEL but I did feel an intermittent hesitation prior to the work. Running the oem Motorcraft Platinum Finewire. Also replaced the wires and coil pack.

Starts up and runs great now.

Thanks
 






koda2000

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if the oil was only found on the treads of the plug (and not the tip) you probably have a leaky valve cover. no big deal. if there was oil fouling on the tip of the plug, you're looking at either a leaky valve seal or worn piston rings/cylinder walls.
 






alohamonte

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1998 Explorer 4.0 4x4
It was wet on just the threads.

I research the valve cover bit more and looks like a plugged oil drainback hole at the top of the cylinder head can definitely cause this situation.

While the valve covers are off (first time in 180,000 miles) should I do any other recommended preventive maintenance?
 












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