The aircraft was in the maintenance shop for correction of a rough running engine at climb power, with accompanying fuel flow fluctuations. The maintenance department replaced the fuel pump, flow divider and the engine spark plugs. The accident flight was a post maintenance test flight to approve the aircraft for return to service. The airplane was on the second touch and go departure when the engine quit and aircraft collided with the ground during the attempted forced landing. The engine was test run using the components in the aircraft and would only run very rough at no higher than 1400 RPM. An obstruction was found in the fuel control unit. Optical examination of the foreign object revealed that it was similar in composure, color and texture to fuel system seal material. The engine was manufactured in July of 1990 and installed in the airframe on August 14, 1990. The fuel control unit was supplied by Continental already installed on the engine. As of the accident, the engine had accrued a total time of 256 hours.