Compression buildup in sump

I have a 1992 Toyota Corolla 1.6 with a 4AF engine. On a trip last week it lost power and built up compression in the sump, and missing on no 2 piston. We have checked to make sure all 4 plugs are firing, and replaced cylinder head gasket. Have also check to make sure all the valves are ok. Can anyone perhaps give us any suggestions as to what can be wrong.