What was found
RT DUCT PRESSURE 10 PSI BLEEDS ON PACKS AUTO ISO VALVE AUTO TRIM AIR ON LEFT DUCT PRESSURE 20 PSI. GROUNDED - YES. PERFORMED FIM 36-10 TASK 804 PARA G FOR LOW DUCT PRESSURE DURING GND IDLE/TAXI. TESTED HIGH STAGE VALVE & REGULATOR PER AMM 36-11-00 AND BOTH FAILED. REMOVED AND REPLACED HIGH STAGE REGULATOR PER AMM 36-11-07. REMOVED AND REPLACED HIGH STAGE VALVE PER AMM 36-11-06. LEAK AND OPS CK GOOD. PERFORMED CONFIRMATION ENGINE RUN AND NR 2 ENG DUCT PRESS WAS 21 PSI, ALL INDICATIONS NORMAL.