As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AT CRUISE POWER, ENGINE RAN ROUGH AND MISSED. RETURN TO DEPARTURE AND FOUND RT MAGNETO TO BE THE PROBLEM. MAGNETO WAS INSTALLED NEW IN THE ACFT ON 01/28/2014. TOTAL TIME ON MAGNETO WAS 26.0 HOURS UNTIL FAILURE. INSTALLED NEW MAGNETO, CHECKED SATISFACTORY.