The Collaborative International Dictionary of English v.0.48:

backfire \backfire\, back fire \back fire\
   1. A fire started ahead of a forest or prairie fire to burn
      only against the wind, so that when the two fires meet
      both must go out for lack of fuel.
      [Webster 1913 Suppl.]

   2.
      (a) A premature explosion in the cylinder of a gas or oil
          engine during the exhaust or the compression stroke,
          tending to drive the piston in a direction reverse to
          that in which it should travel; also called a knock
          or ping.
      (b) an explosion in the exhaust passages of an internal
          combustion engine.
          [Webster 1913 Suppl. +PJC] Backfire

The Collaborative International Dictionary of English v.0.48:

Backfire \Back"fire`\ Back-fire \Back"-fire`\, v. i.
   1. (Engin.) To have or experience a back fire or back fires;
      -- said of an internal-combustion engine.
      [Webster 1913 Suppl.]

   2. Of a Bunsen or similar air-fed burner, to light so that
      the flame proceeds from the internal gas jet instead of
      from the external jet of mixed gas and air. --
      Back"-fir`ing, n.
      [Webster 1913 Suppl.]