As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
LEFT ENGINE BEGAN CONTINUOUSLY BACKFIRING AFTER LEAVING 2,000 FEET. ALL PRESSURES WERE NORMAL, TORQUE METER FLUCTUATIONS BETWEEN BACKFIRES. ENGINE WAS SHUT DOWN AND SECURED, RETURNED TO AIRPORT. NR 1 CYLINDER WAS FOUND CRACKED AT EXHAUST PORT. CYLINDER REPLACED AND AIRCRAFT RETURNED TO SERVICE.