What was found
LEFT ENG OFF LIGHT ON & LT ENG BLEED OFF EICAS MSG, WITH ENG RUNNING, ENG BLEED SWITCH ON, LT & RT ISOLATION VALVES CLOSED, AC PACK SELECTED TO ON, & PSI IS NORMAL. LT & RT PSI ARE DURING CRUISE. BITE CHECK OF AIR SUPPLY MODULE FAULTS "PRSOV". 1 EA 641-9276 VALVE. REPLACED PRV CONTROLLER & AIR SUPPLY CONTROL CARD. BOTH, NO HELP. REPLACED PRSOV, OPS GOOD.