Motor only runs when a spark plug is removed

2002 ford explorer 4.6 won't start unless a
spark plug is removed. Coolant busted out
up from behind engine. Started running
terrible now it won't run unless a spark plug
is removed. Why will it only run while a plug
is removed?
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Answers
Coolant "BUSTED" out? Hydro locked? Head gasket? Lots of miles???
I also wonder, if not a head gasket, if the valves are not opening on that cylinder for some reason.