What was found
DIFF PRESSURE EXCEEDED LIMITATION. 8.5 AT FL380CREW FL380 DIFFERENTIAL PRESS WAS 8.5 AND RISING. WENT TO 8.9. M AX WAS 8.3 OPERATING LIMIT. DESCENDED DOWN TO FL 240. WENT DOWN TO 7.8 AND AND BACK UP TO 8.5 . AT 20000 WENT TO 8.0 AT 20000 C ABIN ALT WAS AT 0 AND SHOULD HAVE BEEN AROUND 3000FT. NEEDLE NEV ER WENT BELOW THE DIFFERENTIAL PRESSURE LIMITATION UNTIL THEY W ERE AT FL140. DIDN'T NOTICE ANY CHANGES WITH POWER SETTING AND 0 2 MASKS DID NOT DEPLOY. CA BELIEVES IT TO BE AN OVER PRESSURE. PRESSURIZED AIRCRAFT REF AMM 21-00-05-780-801 TO 4 PSID. NO HULL LEAKS FOUND. AFTER 4 PSID CLOSED OUTFLOW VALVE COMPLETLY AND TURNED BOTH PACKS OFF. AFTER 2 MINUTES PRESSURE WAS AT 2.5 AND RATE OF CHANGE NEVER EXCEEDED 1.5. ROTABLE PARTS CHANG ROTABLE PARTS CHANGE WAS INDICATED - TT # 1369988 SN OFF 9763 IPC REFERENCE # 21-31-00 VALVE, AIR, CAB OFF 29-2131-9-0007 0524 ON 29-2131-9-0007 9763 REMOVED AND REPLACED AFT OUTFLOW ASSEMBLY REF AMM 21-31-03-000/400-801. OUTFLOW VALVE ASSEMBLY FAILED PRESSURIZATION GROUND TEST REF AMM 21-31-00-700-802.SUSPECT OUTFLOW VALVE ASSEMBLY BAD FROM STOCK STILL REQUIRES REPLACEMENT.