You either a have a really bad intake manifold gasket (on cyl # 4 where the coolant can pour directly into the cylinder via intake runners) Or you have a crack in a coolant passage in the head(or on spark plug tube I have seen them fill a cylinder this way). Or you can have a severely blown headgasket. Or you may have cracked a sleeve. Depending on tuning, boost pressures would help narrow some of those out.