On April 3, 2003, at 1822 Pacific standard time, an experimental Vortec 99, N6052T, collided with obstacles during a forced landing at Gillespie Field, El Cajon, California. The forced landing was precipitated by a loss of engine power while operating above the airfield. The flight was operated by the pilot/owner under the provisions of 14 CFR Part 91. The private pilot was not injured and the airplane was substantially damaged. Visual meteorological conditions prevailed. The flight originated at Gillespie Field about 1800, and no flight plan had been filed. The pilot reported to the National Transportation Safety Board investigator that he had been working on the airplane engine, and was performing a test flight at pattern altitude over the airfield when the engine began to "run rough and quit." The airplane landed short of the runway, struck a fence post, and came to rest in the threshold area of the approach end of runway 17. The engine was a Chevrolet, 4.3L, V6. The pilot reported that the cause of engine failure was unknown.