On July 3, 2007, about 1500 eastern daylight time, a Mooney M20E, N7837V, was substantially damaged during a forced landing, following a loss of engine power while in cruise flight, near Winnsboro, South Carolina. The certificated flight instructor (CFI), and the certificated commercial pilot were not injured. Visual meteorological conditions prevailed and no flight plan had been filed for the flight that departed Columbia Metropolitan Airport (CAE), Columbia, South Carolina, about 1445, destined for the Fairfield County Airport (FDW). The instructional flight was conducted under 14 Code of Federal Regulations Part 91. The CFI reported that the commercial pilot was receiving dual flight instruction towards a flight instructor certificate. They had completed a simulated engine failure and were in cruise flight at an altitude of 2,200 feet mean sea level, when the engine rpm suddenly dropped to 800 rpm. The CFI was not able to restore engine power, and performed a forced landing to a field. During the landing, the airplane's left wing struck a tree stump, and was substantially damaged. Examination of the airplane was conducted by a Federal Aviation Administration (FAA) inspector. The engine was removed and subsequently test run on July 27, 2007. After some initial troubleshooting, the engine was started. It ran rough, with intermittent surges and exhibited characteristics of running with a lean mixture. After the fuel injector servo was removed and a replacement installed, another test run was attempted. The engine started and ran smoothly through 2,500 rpm. In addition, all temperatures and pressures were within their normal operating limits. The fuel injector servo was subsequently examined at it's manufacturer, under the supervision of an FAA inspector. The examination revealed that the fuel inlet screen had more than 50 percent of its exterior surface covered in light brown corrosion/contamination, and two-thirds of the inlet fitting was blocked by debris. In addition, contamination was noted throughout the fuel injector servo. The engine and fuel injector servo were both overhauled in July 1993, and had accumulated about 690 hours of operation. The airplane had been operated for about 5 hours since its most recent annual inspection, which was performed on April 1, 2007. The airplane manufacturer's annual inspection guidelines included inspecting the fuel injection system, and cleaning the screens per the engine manufacturer's recommendations.