What was found
(CAN) AFTER TAKEOFF WHILE CLIMBING THROUGH 8000 FT, CREW REPORTED LOW MOP WARNING LIGHT ANNUNCIATED IN COCKPIT. CREW PULLED POWER BACK TO IDLE BUT MOP CONTINUED TO DROP TO ZERO. CREW SHUTDOWN ENGINE AND RETURNED TO FIELD WITHOUT INCIDENT. PRESSURE ADJUSTING VALVE WAS ADJUSTED DUE TO LOW OIL PRESSURE READING. GROUND RUNS WERE COMPLETED AND MAP READINGS WERE NORMAL. THE AIRCRAFT RETURNS TO SERVICE.