What was found
DURING CLIMB-OUT, THE CREW REDUCED POWER TO 92% AND NOTICED THAT "L ECU A" AND "L ECU B" FAIL WARNINGS APPEARED, ACCOMPANIED BY A LOSS OF POWER. THE CREW CONTINUED THE CLIMB, AND BOTH "L ECU A" AND "L ECU B" FAIL WARNINGS CLEARED, ALTHOUGH OIL WAS OBSERVED LEAKING FROM THE LEFT-HAND ENGINE. THE CREW PROCEEDED TO LAND AND SHUT DOWN THE ENGINE UPON EXITING THE RUNWAY. A BORESCOPE INSPECTION REVEALED THAT THE LEFT ENGINE #4 CYLINDER HAD A HOLE BURNED THROUGH THE TOP OF THE PISTON.