As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING A ROUTINE TRAINING FLIGHT, THE ENGINE BEGAN TO RUN ROUGH AND, INTERMITTENTLY, STOP RUNNING. THE ENGINE LOST POWER AND THE CFI WAS FORCED TO LAND IN A SOFT FIELD. AFTER THE ACFT WAS RECOVERED, THE ENGINE WAS TEST RUN. THE LEFT MAG WAS INOPERATIVE. THE LEFT MAG WAS REMOVED AND INSPECTED. THE CONTACTOR IN THE DISTRIBUTER GEAR HAD BECOME DISLODGED FROM THE GEAR. THE LOOSE CONTACTOR WOULD INTERMITTENTLY CAUSE IGNITION CROSSFIRE.