As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
ON DESCENT AT 75 PERCENT N1 GET L BLEED & L DUCT PRESSURE OSCILLATING 25-45 PSI. REPLACED FAN AIR MODULATING VALVE PER MM. PERFORM HIGH POWER RUN, STILL HAVE FLUCTUATING BLEED PRESSURE ON L ENG. REPLACED PRSOV LT ENGINE, COMPLETED POWER RUN BLEED SHIFT CHECKS NORMAL.