No start

Working on my dads vehicle, it started a few weeks back with his car not starting in a store parking lot. Got him towed back to the house and I checked for spark first. All his points where burnt and corroded. So I replaced cap and rotor, ignition coil and all spark plugs and wires. The car finally started and ran fine for a week or so, then it happened again. So I replaced the ignition module and it started up ran fine now it happened again. On further inspection the ignition lock cylinder was alittle lose and faulty, so we replaced that the car started right up and then died. The fuel pump and relays are in good shape, no bad fuses. Just looking for further advice not the best auto mechanic but as far as I can tell I have fuel and spark. The engine does crank but intermittently starts. Thanks.