1996 Ford Probe GT piston not firing.?

I have a 96 Ford PGT and my sixth piston is not firing. the distributor cap is good, the spark plug wires and spark plugs are brand new and they are all (including the sixth) firing. my fuel pressure is fine, and the chamber is getting fuel. so... help!! i'd really appreciate a walkthrough on how to figure this out and preferably fix it inexpensively..