blowing steam doesn't necessarily mean the radiator is bad. all that means is the engine is overheating. It could be a bad water pump. Low on coolant. Air pockets vapor locking the coolant flow. a bad thermostat. a blown head gasket will do that too.

as for your injectors, it could be the injectors are bad, but it could also be spark. All pulling the plug off tells you is that, that cylinder is the one not firing. You should pull your full rail off and spray the injectors on a piece of card board or something by turning the engine over. They should all spray pretty much the same. If #3 and/or #4 isn't spraying or not spraying enough, then you know that injector is bad. If all of them do spray, then you know it is spark related and not the injectors. Start with the spark plugs, then wires, then cap and rotor, then a different (known to be good) coil, then a different (known to be good) distributor. One at a time til the problem is fixed.