What makes a car backfire?

Answer 1

bad ignition timing is correct. The timing gears may have slipped, and if the timing system uses a belt instead of a chain then the belt could have worn. The timing systen keeps the intake, exhaust and cyclinder pistons all in time so the engine will fire correctly. If the belt or chain slips even just a small amount, then the valves let gas in or out before or after the piston is at the point where the cylinder shout fire the spark plug. If the belt or chain slip far enough the engine will not fire at all.

Bad ignition timing or fuel getting to the exhaust.