P0303 #3 cylinder misfire

Hey guys,
My 99 Explorer (4.0 106,000 miles) had the check engine light come on after mechanics replaced plugs. The code was P0303. The mechanic replaced the
plug and spark plug wire saying the plug wire was causing an arc to the spark plug. Well, the light came back on, for the same cylinder. Is there any other things that I should look for that would cause a cylinder misfire?
Thanks in advance.
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I have a 98 Explorer 5.0 and had the same problem(s). I first got a tuneup and/or 90,000 mile service. That fixed it for awhile (new plugs, fuel filter, timing adj.etc.). After a week, the CEL came back on, took to AZone had them check, found out it was Cyl. 5 & 7. Drove next day and CEL went off. The next week it came on, took it to Advance Auto to check, found out to be Cyl 5 & 7 again. Told the guy what had been done to car, service etc. and he said it may be the wires. Replaced wires. Problem went away for another week. These were all short drives, around town and back and forth to work. Drove Explorer to mountains, 3 hour drive. No CEL. drove home, still no CEL. Drove to work and around town, CEL came back on. So the On then Off syndrome still lasted for a week until yesterday, the CEL came on, engine was idling bad, really moving and grooving under the hood. Took it to Ford Dealership today. Still waiting for results.
Lance wrote:

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Thanks for the reply. Mine is in the shop now. They(mechanic) thought it may be a intake issue, but after speaking with them, they are looking into a head issue now. Will post the results when I find out what they are. This may sound odd, but I do not recall any symptoms before I had the tune-up(plugs, fuel filter). Since the tune up, at least once every couple weeks, it has been in to get repaired. The CEL never came on until after it left the mechanic the first time. Second time it went in, was for a coolant flush and CEL was on. It came up with cylinder 3 misfire. Now after a day or so of driving around town the same code comes back. I never had to replace much coolant, just add a little to the reservoir once every six months. Nothing that seemed out of the ordinary.
Lance

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Well,
The problem seems to have been both heads were cracked. Ordered new ones. Should be in after a couple days. I cannot wait to get it up and running. Its surprising how much you miss driving a vehicle when you are without it.

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