As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
BOTH ENGINES SLOW TO START DUE LOW PRESSURE. APU DUCT PRESSURE 20 PSIG MAX DURING ENGINE START. AIRFLOW AUDIBLE IN FLIGHT DECK WITH PACKS OFF & NR 1 ENGINE BLEED ON. ACFT GROUNDED. LEFT PACK FLOW CONTROL & SHUTOFF VALVE BYPASSING AIR. REMOVED & REPLACED THE LEFT PACK FLOW CONTROL & SHUTOFF VALVE IAW AMM 21-51-01. OPS & LEAK CHECKED GOOD. BOTH ENGINES NOW START NORMAL IAW AMM 71-00-00-800-808-F00.