You need compression, spark and fuel. The misfire cylinder is missing one of those. Do a compression test to see if the valves and rings are okay, all cyinders should be within 10% of each other....
Out of gas, blown fuel pump fuse, bad fuel pump, bad fuel pump relay, clogged fuel filter, loose or corroded wiring, defective fuel pressure regulator, or in rare instances a defective computer.
missfiring cylinder possibly due to fouled spark plug, ignition timing incorrect (leads swapped around). The reason for the backfire is unburnt fuel accumulates in the very hot exhaust system and...