Definitions of backfire:

• noun:   a miscalculation that recoils on its maker
• noun:   a loud noise made by the explosion of fuel in the manifold or exhaust of an internal combustion engine
• verb:   emit a loud noise as a result of undergoing a backfire

  Example: "My old car backfires all the time"

• verb:   have an unexpected and undesired effect

  Example: "Your comments may backfire and cause you a lot of trouble"

• verb:   set a controlled fire to halt an advancing forest to prairie fire