As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AT APPROXIMATELY 1600 LOCAL FLYING FROM KPDK TO KGSO AT CRUISE DEVELOPED AN ENGINE VIBRATION AND ROUGH RUNNING. DIVERTED INTO KGMU WITH 1 PASSENGER, WITHOUT INCIDENT. AFTER GROUND CHECKS FOUND THAT A SPARK PLUG FIRING SIDE INSULATOR WAS CRACKED CAUSING THE MISS FIRE.