On August 20, 2009, about 1600 eastern daylight time, a Cessna A188B, N4842R, sustained substantial damage when it impacted a field during a forced landing in McRae, Georgia. The certificated commercial pilot was not injured. Visual meteorological conditions prevailed and no flight plan was filed for the local aerial application flight. The flight was operated under the provisions of 14 Code of Federal Regulations Part 137. The flight originated at Telfair-Wheeler Airport (MQW) McRae, Georgia, at 1545. According to the pilot, while spraying chemicals on a field, the engine oil temperature started rising while the oil pressure was dropping. He exited the field and noticed the engine was losing power rapidly. The oil pressure went to zero and the engine then lost all power. The pilot initiated an emergency dump of the spray solution and attempted to climb, but was unable to do so because of low airspeed. He initiated a forced landing into a soybean field. The nose and engine compartment came to rest in the dirt and the landing gear collapsed. The pilot stated that fuel leaked from the right fuel tank. Examination of the airplane by a Federal Aviation Administration (FAA) inspector found the airplane on its belly with substantial damage to the firewall, engine mounts, fuselage attachments, and the left wing. The airplane was recovered for further examination. Examination of the engine revealed that the engine remained attached to the airframe, and had light impact damage on the front of the oil sump. Some heat damage was observed on the crankcase vent tube. The top spark plugs were removed and the crankshaft was rotated using the propeller. Compression was confirmed on all of the cylinders, and continuity was confirmed to the rear of the engine and the magneto drives. Both magnetos were in place and not damaged. The magnetos were rotated at high speed and no spark was observed on any of the magneto terminals on either magneto. They were both disassembled and the points on both magnetos had severe wear and burning damage. The points would not separate when the drive shafts were rotated. Evidence of arcing was observed in the interiors of both magnetos. The top spark plugs had normal wear when compared to the Champion Check A Plug comparison chart. They all had dark deposits in the electrode areas. The oil filter had light impact damage. It was opened and metallic particulates were observed in the filter element. The engine was prepared for an attempted engine run. Both magnetos were replaced with operational Slick-6310 magnetos. Both sets of ignition harnesses were replaced and the spark plugs were replaced on the right side with Champion RHB-32E spark plugs. The oil filter was replaced with a champion oil filter, and after several start attempts the starter was replaced. The airplane battery was replaced for the run attempts. Numerous attempts were made to start the engine using two different starters and several different batteries. All of the attempts failed, and the engine was sent to the manufacturer for further examination. The examination found the throttle body and mixture control assembly was tested and found to have abnormal flow through the return fitting at full rich with a leak at the mixture shaft. The unit was disassembled and scoring was found on the interface surfaces of the mixture control shaft and fuel metering plug. Disassembly of the engine showed the numbers 1 and 4 piston heads exhibited thermal erosion consistent with a pre-ignition/detonation event. A review of the engine logbooks found that the engine was overhauled on May 3, 2006. The last 100 hour inspection was completed on October 3, 2008.The airplane flew 105 flight hours since this inspection.