Ford Repair: ford explorer #3 cylinder spark plug fowls out, xls model, ford dealer

Question
QUESTION: I have had this repaired by both ford dealer and indepedant mechanics only for problem to return within 3,000 miles....the problem is that the number 3 cylind spark plug fowls out. The car runs fines until I get around 3,000 miles on it after thr replacement of the spark plugs. The explorer is a 2000 XLS model with 146879 miles on it. Any ideas....?

ANSWER: Is it gas fouling, oil fouling, or what?

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QUESTION: I have not been told...never thought about that aspect of it...give both scenario's

Answer
We need to find out to make a proper adjustment. If it is gas fouling, try replacing the injector. If it is oil fouling, run a compression test. You might try using a fouler tip for the plug in the time being. Is there any rust or corrosion on or around the outside of the spark plug?