What was found
RIGHT & LEFT BLEED DUCT PRESSURES SPLIT BY GREATER THAN 20 PSI IN CRUISE. RIGHT = 44 LEFT = 22 AT FL 340/ .79M, ENGINE BLEEDS ON, APU BLEED OFF, TAI OFF, PACKS AUTO. ACFT GROUNDED. PERFORMED BLEED SYSTEM HEALTH CHECK IAW TC NG-36WC-00001. FOUND BLEED AIR REGULATOR AND PRECOOLER CONTROL VALVE BAD. REPLACED BLEED AIR REGULATOR IAW AMM 36-11-03. REPLACED PRECOOLER CONTROL VALVE IAW AMM 36-12-02. ACCOMPLISHED ENGINE BLEED CROSSOVER OPS TEST WITH NO PRESSURE SPLIT NOTED IAW AMM 36-11-00-710-801.