Engine Power Loss
While in cruise flight, the engine oil pressure decreased and the oil temperature increased. The engine lost power rapidly and subsequently quit. The pilot performed a forced landing onto a four-lane highway.
Pilot Actions
According to the pilot, he maneuvered the airplane to avoid a collision with electrical power lines and vehicles. To prevent the landing gear from catching on power lines, it was not extended. After touchdown on the highway, a vehicle backed into the road and was struck by the right wing tip.
Post-Accident Examination
A post-accident examination of the engine revealed that the number 2 piston exhibited signs of pre-ignition/detonation, specifically a hole burned in the piston. Testing of the engine fuel system demonstrated that it was capable of providing the required fuel to the engine. The pilot reported that the airplane was full of 100LL fuel when the flight departed.
Cause Determination
Excessive fuel leaning, during improper usage of the mixture control, will result in engine detonation.