After changing the EGR valve in my 95 Windstar I was able to clear the original set of 4 DTCs. I took the van on a test drive and a new DTC came up, a P0304, misfire on cylinder 4. Which turned out to be accurate. I pulled the #4 sparkplug and it was worn - the electrode was worn beyond recognition.

Question is, what causes the electrode to get so distorted?

Lack of fuel or too much electrical input?