What was found
AFTER ENGINE STARTS, L BLEED AIR DUCT PRESSURE @ 10 PSI (R@20). WITH #2 BLEED AIR SWITCH OFF, AND ISOLATION VALVE OPEN, BOTH DUCT PRESSURES DROP TO 10 PSI. GROUNDED - YES. TROUBLESHOT LH ENG BLEED SYS PER B737-900 AMM 36-00-00. FOUND PRSOV LEAKING AT DIAPHRAGM AND SENSE LINE BOSS ATTACHMENT. REMOVED AND REPLACED PRSOV, HIGH STAGE VALVE AND HIGH STAGE REGULATOR AFTER PERFORMING B737-900 FIM TASK 36-10-810. REF AMM 36-11-04, 36-11-06 & 36-11-07. PERFORMED GROUND VERIFICATION TEST 36-11-00-710-801 TEST PASSED.