On October 27, 1993, at 1845 central daylight time, a Beech F33A, N6333Y, registered to James B. Griebel Farms of Fridley, Minnesota, and operated by an instrument rated private pilot, experienced a loss of engine power. A night forced landing was initiated and on landing the airplane impacted a fence and guard rail posts alongside a highway. The airplane sustained substantial damage. The pilot and one passenger reported no injuries. A second passenger reported minor injuries. The business 14 CFR Part 91 flight was operating in visual meteorological conditions. An IFR flight plan was on file with the intended destination of Saint Louis, Missouri. The flight departed Anoka, Minnesota, at 1820. Prior to departure the mechanical fuel pump had been removed and replaced to comply with an Airworthiness Directive. The accident flight was the first flight after the maintenance. The pilot stated that while the airplane was in cruise flight he noticed a drop in fuel pressure. The pressure drop continued until power was lost and it became necessary for him to make a forced landing. On examination it was found that the fuel line "B" nut had backed all the way off the flare nut fitting at the mechanical fuel pump. During the examination the nut was hand threaded onto the fitting and no other discrepancies were noted.