As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
PUMP OUTPUT DECREASED AS ENGINE WARMED UP UNTIL IT BECAME UNACCEPTABLE AT LOWER RPM. AT 1000 RPM PRESSURE DROPPED BELOW 3 INCHES ON INDICATOR. TESTED AIR SYSTEM FOR LEAKS AND FOUND NONE. CHECKED REGULATOR AND MANIFOLD VALVE, REPLACED BOTH THE SYSTEM STILL FAILED TO MAINTAIN PROPER PRESSURE. SO REPLACED ENGINE DRIVEN AIR PUMP AND SYSTEM PASSED.