As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
PILOT REPORTED INSTRUMENT AIR PRESSURE WAS LOW AT 1700 RPM. UP ON TROUBLESHOOTING THE MECHANIC NOTICED ON INITIAL RUN UP PRESSURES WERE WITHIN LIMITS, AFTER ENGINE STARTED TO WARM UP THE PRESSURE STARTED TO DROP BELOW LIMITS. INSTALLED NEW PUMP, DURING GROUND RUN MECHANIC NOTICED AFTER ENGINE STARTED TO WARM UP OUTPUT PRESSURE STARTED TO DROP. INSTALLED ANOTHER AIR PUMP SYSTEM WORKED NORMAL. NO PROBABLE CAUSE OR RECOMMENDATIONS AT THIS TIME.