Misfire in cylinders three and four

Odd misfire in cylinder three or four. With both spark plug wires on I get a misfire. If I pull number three wire no difference missing. If I pull four no difference it is missing. If I pull both wires I get a double miss. If I put either wire on one at a time that cylinder three or four that I put the wire on will fire, put both back on and it misfires. It will do the same if I pull number three injector wire or number four. Whatever one I put back on without putting the other one back on it will fire.