What was found
AIRCRAFT WAS GROUNDED: FLIGHT RETURNED TO DFW ON ACCOUNT OF PRESSURIZATION ISSUE. AN EMERGENCY WAS DECLARED. PILOT REPORTS PRESSURIZATION LIGHT CAME ON AT 8000 IN CLIMB. CABIN RATE WAS CLIMBING AND INCREASING. MAINTENANCE REPORTS DURING ENGINE RUN LEAK CHECKS, FOUND FORWARD FUSELAGE PRESSURE RELIEF VALVE OPEN, UNABLE TO PRESSURIZE A/C. REPLACED WITH NEW VALVE IAW JOB CARD 5356. OPS CHECKED GOOD. RAN ENGINES FOR 20 MINUTES AT CRUISE AND ACCOMPLISHED FUSELAGE LEAKAGE CHECK IAW AMM 21-00-00, TEST PASSED.