What was found
DUCT PRESSURE SPLIT BETWEEN 15-20 PSI AT HIGH POWER SETTING PRESSURE SPLIT DROPS TO 5 PSI AT LOW POWER SETTING. GROUNDED - YES. RAN BOTH ENGINES AT IDLE. DUCT PRESSURE LOW ON #1 ENG. PERFORMED BLEED AIR HEALTH CHECK ON #1 ENG PER T/C NG-36WC-00001. FOUND CONTROL PRESS SENSE LINE LOOSE AT BLEED AIR REG. RETORQUED LINE AT BAR REF B737-800AMM 36-41-03. OPS CHECK GOOD. REF L/P 60475459 AND 6047560 FOR REPLACEMENT OF HIGH STAGE REG AND PRE COOLER CONTROL VALVE. ENG BLEED AIR CROSS OVER OPS CHECK GOOD. REF AMM 36-11-00.