As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
PILOT REPORTED THE LEFT ENGINE WOULD NOT DEVELOP FULL POWER, STOPPED AT 26 INCHES MAP AND VIBRATION. INSPECTION OF THE LEFT ENGINE REVEALED A PREIGNITION EVENT IN THE NR 3 CYLINDER WHICH CAUSED SIGNIFICANT DAMAGE TO THE PISTON HEAD. THE CYLINDER IS IN THE PROCESS OF BEING REPLACED. SUSPECT SPARK PLUG INSULATOR FAILURE TO BE THE CAUSE OF THIS EVENT. FURTHER DETAILS WILL BE PROVIDED UPON DETERMINATION OF THE SPARK PLUG PERFORMANCE.