What was found
AFTER PUSH BACK & STARTED ALL 3 ENGINES, GOT A LEVEL 3 TANK WING OVERFILL. FOLLOWED QRH & FUEL CONTINUED TO VENT OUT OF THE LEFT WING. STARTED WITH 98,400 LBS FUEL & SHUTDOWN WITH 90.8 BURNED ONLY 610 LBS ON THE ENGINES START LEVEL FUEL TANKS 1. R&R VENT OVERFILL RELIEF VALVE IAW AMM 28-12-05-4. OPS CHECKED IAW AMM 28-12-05-5. OPS CHECKED GOOD. R&R NR 3 TIP TANK CLIMB VENT VALVE IAW AMM 28-12-01-4. AFTER FURTHER INSPECTION, FOUND THE NR 3 TANK INBD CLIMB VENT FLOAT VALVE FLAPPER DOOR BROKEN OFF. R&R INBD CLIMB VENT FLOAT VALVE IAW AMM 28-12-01-4. OPS CHECKED GOOD, XFERED FUEL BETWEEN TANKS NO FUEL FROM VENT BOX.