What was found
NUMBER 1 ENGINE FIRST ATTEMPT ENGINE START HAD WHITE FLASHING BOX EGT. ENGINE SHUTDOWN BY ITSELF. MAX EGT 586C, MAXIMUM N2 GOT TO 455% KALS OAT 39C, POSSIBLE TAILWIND LESS THAN 5KTS. DID QRH PROCEDURE. SECOND ATTEMPT START WAS NORMAL. GROUNDED - YES. ACCOMPLISHED FIM 80-05 TASK 801. NO FAULT HISTORY LOGGED. NO EXCEEDANCES LOGGED. VISUALLY INSPECTED ENGINE INLET + EXHAUST. NO DEFECTS NOTED. REMOVED, INSPECTED + REINSTALLED BLEED AIR CHECK VALVE. NO DEFECTS NOTED FOR VALVE. REF AMM 36-11-02 FOR VALVE REMOVAL AND INSTALLATION. ACCOMPLISHED ENGINE RUN. EGT STABILIZED AT 480C. INPUT MONITORING SHOWED T49.5 S4 OUT OF LIMITS. ACCOMPLISHED EGT CLEANING + ACCOMPLISHED ENGINE RUN. T49.5 VALUES STILL OUT OF RANGE. REF AMM 77-21-01-000-801-F00. REMOVED AND REPLACED ALL 4 T49.5 PROBES S1,S2,S3,S4 PER AMM 77-21-01-000-801-F00/77-221-01-400-801-F00. VALUES ARE NOW WITHIN LIMITS. PERFORMED ENGINE 1 START PROCEDURE PER AMM 71-0-00-800-807-F00, NO DEFECTS NOTED.