On October 9, 2017, about 1616 mountain standard time, an experimental Nanchang China CJ-6, airplane, N8NW, was substantially damaged when it was involved in an accident near Buckeye, Arizona. The pilot sustained serious injuries and the passenger sustained minor injuries. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. The pilot stated that the takeoff, climb, and cruise were uneventful; however, after he initiated a descent toward the destination airport, the engine varied in pitch and rpm. He checked the fuel quantity and both main tanks indicated 60 liters. He enriched the fuel mixture and turned on the auxiliary fuel pump. He stated that the fuel pressure was "good", but as the airplane slowed, the engine eventually lost power. Unable to glide to an airport, the pilot initiated a forced landing to a clearing at a construction site. During the landing, the airplane’s left wing impacted an obstacle, which caused the airplane to veer out of control and resulted in substantial damage to the fuselage and wings. Postaccident examination of the engine revealed that the crankcase sustained impact damage to the lower side. The propeller and spinner were attached to the crankshaft propeller shaft. The crankshaft was rotated by hand and rotational continuity was established throughout the engine. All cylinders exhibited compression and suction in the proper firing order. The left magneto was removed and manually rotated. Spark was observed from the coil lead; however, when rotated, the mechanical advance was sticking. The right magneto was removed and during manual rotation, spark was observed on the coil lead. The forward spark plugs were removed, and the spark plugs electrodes exhibited an oil residue and evidence of normal wear. The engine-driven, rotary gear fuel pump was removed and examined. Examination of the pump’s vanes and drive shaft revealed no anomalies. The pump’s drive shaft rotated freely by hand; however, fuel was noted on the accessory side of the pump. Further examination revealed that the pump’s diaphragm, located on the drive shaft, was ruptured. The diaphragm was designed to prevent fuel system contamination. Remnants of the diaphragm were observed on the accessory side of the pump and the diaphragm was located inward from its original position on the drive shaft. Furthermore, the result of a ruptured diaphragm would/could be consistent with being a potential source of fuel system contamination from air and or oil. The fuel header tank was empty. The fuel line from the gascolator to the engine was intact. The engine accessories mounted to the rear of the engine were intact with the exception of the oil reservoir, which had impact damage. The fuel lines were removed and were clear of debris. The three-bladed propeller was examined. All blades had separated about 1 ft from the hub. The examination of the engine revealed no additional evidence of pre-impact mechanical anomalies.