As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
ROUGH MAGNETO ON RT ENGINE DURING RUN UP. PULLED SPARK PLUGS ON LT MAGNETO SIDE. FOUND ONE SPARK PLUG SHORTED OUT (OUTSIDE ELECTRODE TOUCHING CENTER ELECTRODE). WHEN THE OUTER ELECTRODES WERE TOUCHED THEY WERE FOUND TO BE VERY LOOSE AND FLOATING. SUSPECT THAT SPARK PLUG WAS MANUFACTURED POORLY.