On October 10, 1998, at 1020 hours Pacific daylight time, a Cessna 190, N1087D, sustained substantial damage during a forced landing after a loss of engine power at the Lost Hills, California, airport. The commercial pilot/owner was conducting the personal flight under the provisions of 14 CFR Part 91. He and his two passengers sustained minor injuries. The aircraft departed from Delano, California, at 0920 for a local flight. Visual meteorological conditions prevailed and no flight plan was filed. The pilot stated the engine began to run rough and that he thought he had lost a cylinder. He elected to land at the nearby Lost Hills airport. On final approach, he noticed a truck parked on the approach end of the runway. He attempted to add power but the engine did not respond. Raising the nose of the aircraft provided enough altitude to clear the truck but forced him to land long. The aircraft exited the end of the runway and went into a ditch that was 15 feet wide and 8 feet deep. No fire occurred and the occupants broke the windshield with the fire extinguisher to egress from the aircraft. Approximately 4 feet of each wing tip was crushed. The landing gear was bent and twisted and the fuselage in the cabin area was buckled. One prop blade was bent aft and the cowling was crushed into the engine. The number 4 cylinder head was cracked from its base through the front spark plug hole. An inspection of the engine was conducted at Aircraft Recovery Services in Compton, California, on October 29, 1998. The engine rotated freely and a finger compression test was conducted. Cylinders 1, 2, 3, 5, 6, and 7 produced compression upon rotation of the crankshaft. Cylinder number 4 produced no compression and its piston did not move upon crankshaft rotation. After removal and disassembly of cylinder number 4, the piston skirt was observed to be damaged and the articulating rod was found in several pieces. Although the piston pin was intact, its bushing was fragmented. Examination by the Safety Board's Materials Laboratory disclosed micro fissuring, indicative of high stress fatigue cracking, on an undamaged area of one fracture surface. The fatigue initiated at the corner of the I-beam section of the connecting rod and propagated through its cross section.