Do you know how many miles are on this engine? Usually a backfire is related to timing, either in the valve train or ignition timing. A worn or flat cam can run rough and maybe cause a backfire. Sticking valves won't open and close as they should and cause a backfire that might clear up when warm... I'd check all the basics, and then look deeper. A vacuum gauge on the intake will tell you all about the status of the valve train. Good luck.
86 ranger 4x4 2.3l efi gas non turbo 5 speed. Small lift. 2.25 in exh w/turbo muffler, no cat or egr. New cam, lifters, rocker arms (stock grind). New fuel pump in tank.