As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING ENGINE RUN UP PRE MAINTENANCE MECHANIC NOTICED AN EXCESSIVE MAG DROP ON RT ENGINE LT MAG. CHECKED PLUGS AND MAG TIMING NO ISSUES NOTED. INSPECTED IGNITION LEADS AND FOUND B4 LEAD OPEN. IGNITION LEAD PHYSICAL INSPECTION IS GOOD. FAILED INTERNALLY AT 243.6 HOURS SINCE NEW