What was found
LEVEL 2 FUEL QUANTITY USED CHECK ALERT ILLUMINATED APPROXIMATELY 25 MINUTES INTO FLIGHT. ACCOMPLISHED THE CHECK LIST, THEN RAN FUEL SYSTEM IN MANUAL WITH NO APPARENT LOSS OF FUEL FOR APPROXIMATELY 30 MINUTES. RETURNED SYSTEM TO AUTO AND OBSERVED ABNORMAL DEPLETION OF FUEL. PRIOR TO RUNNING CHECK LIST WE WERE SHORT APPROXIMATELY 3600 TO 4200 LBS OF FUEL. REPLACED THE FUEL QUANTITY DATA CONTROL UNIT.