What was found
AFTER ENGINE START ON MAUI DUCT SPLIT OF 11 PSI WITH LEFT SIDE LOW. ON CLIMBOUT SPLIT TO 19PSI (LEFT LOW). AT CRUISE SPLIT STARTED AT 13 AND DECREASE DURING FLIGHT TO 6 PSI. ON DESCENT NEEDLES WERE MATCHED. MINIMUM PRESSURE 25 PSI ON LEFT 45 PSI ON RIGHT. ON DEFERRAL. PERFORMED TROUBLESHOOTING PER T/C NG 36 WC 00001 & FIM TASK 36-10-00-810-80. FOUND NR 1 BAR OUT OF LIMITS PRECOOLER CONTROL VALVE NR 1 ENGINE FAILED. REPLACED PRECOOLER CONTROL VALVE PER AMM 36-12-02. REPLACED BLEED AIR REGULATOR ON NR 1 ENG. PER AMM 36 11 03. BLEED AIR REGULATOR OPS CHECKED GOOD. OPS & LEAK CHECKED GOOD, OK FOR SERVICE. REPAIR CONFIRMATION PERFORMED PER FIM TASK 36-10-00-810-804 & OPS CHECKED GOOD.