As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
LT DUCT PRESSURE FLUCTUATES DURING TAKEOFF OR CLIMB, WITH L & R ISOL VLVS CLOSED, & BLEED SW ON. DUCT PSI FLUCTUATES BETWEEN. CREW COMMENTS: SPLIT DURING CLIMB. NO SPLIT AT CRUISE. PRESSURES: L-20 R-3. REPLACED PRESSURE REGULATING VALVE CONTROLLER.