On July 28, 2024, about 1130 central daylight time, a Piper PA-46-310P airplane, N4646G, sustained substantial damage when it was involved in an accident near Radisson, Wisconsin. The commercial pilot sustained no injury. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal cross-country flight. The airplane departed from the Lake in the Hills Airport (3CK), Lake in the Hills, Illinois, about 0930. Before departure from 3CK, the pilot reported the airplane had 85 gallons of 100 low-lead fuel onboard. The airplane, operating on an instrument flight rules flight plan, traveled to the northwest, toward the destination of the Sawyer County Airport (HYR), Hayward, Wisconsin. About 25 miles southeast of HYR, the reciprocating engine sustained a total loss of power, and the pilot declared an emergency to air traffic control. The pilot performed a forced landing to a rural grass field containing trees. The airplane came to rest upright, and the pilot was able to egress from the airplane without further incident. The airplane sustained substantial damage to the fuselage and the empennage. An on-site examination of the engine by the FAA found that a cap was missing from the fuel pressure test port (a 90° brass elbow port) near the front top of the engine. The test port had blue staining present, and the exposed threading was found intact. The test port is where a gauge would connect during maintenance work to test the fuel pressure. The aluminum housing that the port connects to also had blue staining present. The missing cap was not recovered. A J.P. Instruments Engine Data Monitor 900 unit was removed from the airframe and the engine performance data was downloaded and reviewed. The engine performance data showed that the fuel flow rate had increased up to the maximum reading, about 80 gallons per hour, at the time the total loss of engine power occurred. Per the engine manufacturer the fuel system is a closed system. With the test port cap off, it becomes an open system, as shown with the blue staining in the two areas. As fuel is lost, fuel pressure is lost, and the engine then quits. A review of the most recent airplane maintenance records showed than an annual inspection was performed on the airframe, engine, and propeller on June 14, 2024, about 6 weeks before the accident. The records reflected work completed on the fuel injection system, including the installation of new fuel injectors. The entries for the annual inspections stated that the airplane was found in to be in an airworthy condition and the airplane was returned to service. According to the Continental Motors Standard Practice Maintenance Manual M-0, a fuel system operational check is required if fuel injectors are replaced. Test equipment is connected to the fuel pressure test port and a test is performed. Once the test work is completed, a cap (Continental Motors part number 639494) is required to be tightened and torqued on the test port. Continental Motors Standard Practice Maintenance Manual M-0 includes a warning that states: Failure to connect and torque fuel system fittings to the proper specification will result in a fuel leak and potential fire hazard. The individual who performed the most recent annual inspections on the airplane did not hold an airframe and powerplant certificate, nor did he hold inspection authorization. The non-certificated mechanic signed off the annual inspections and returned the airplane to service using the airframe and powerplant mechanic certificate number of his deceased father, who held inspection authorization. The father passed away on June 25, 2007.