What was found
ON CLIMBOUT, DUCT PRESSURE DIFFERENTIAL NOTED AT GREATER THAN 20PSI (R 42PSI / L 45PSI). ON LEVEL OFF AT FL340 DUCT PRESSURE NOTED AT R 43PSI / L 26PSI. GROUNDED - YES. ACCOMPLISHED #1 ENG BLEED AIR SYSTEM HEALTH CHECK TASK CARD NG-36WC-00001 & FOUND PRECOOLER VALVE FAILED TEST. REMOVED #1 ENG PRECOOLER VALVE REF B737-900 AMM 36-12-02-000-201 & INSTALLED SERVICEABLE PRECOOLER VALVE REF AMM 36-12-02-400-801. LEAK & OPERATIONAL TEST GOOD. REF AMM 36-11-00-710-801 & TASK CARD NG-36WC-00001 FOR ENGINE HIGH PWR RUN & HEALTH CHECK TASK CARD NG-36WC-00001. DUCT PRESSURE WITHIN LIMITS NOW.