What was found
HAD PACK 2 MEL. FOLLOWED MEL PROCEDURE FOR THAT WITH ECS OFF AND APU ON. ON TAKEOFF 1000-1500 AGL, BLEED 2 OVERPRESSURE EICAS. ECS PAGE SHOWED 150 PSI AND AMBER CROSS OVER BLEED 2. RAN QRH AND TRIED TO RESET BUT REMAINED ANNUNCIATED. WE LEVELED OFF AT 10,000 FT WHICH REDUCED THRUST WHICH THEN REDUCED THE PSI AND MESSAGE EXTINGUISHED. BUT AFTER REAPPLYING POWER, PSI INCREASED TO OVER 100 PSI AND MESSAGE CAME BACK ON. CONTINUED QRH TO HAVE ENGINE 2 AT IDLE THEN BLEED 2 PSI WAS AROUND 13 REST OF THE FLIGHT. THEN RETURNED TO DFW SINGLE ENGINE. (EMERGENCY DECLARED). NO RECENT HISTORY NOTED. ENERGIZED AIRCRAFT IAW AMM 24-42-02 AND INTERROGTED CMC, FOUND RH BLEED 2 PRSOV OPEN. TROUBLESHOT IAW FIM 36-11-00 AND PERFORMED BLEED 2 CH 1 IBIT TEST, TEST PASSED. NO RELATED MESSAGES ON EICAS.