What was found
AIR TURN BACK. DURING CLIMB BOTH LT AND RT MANIFOLD PRESSURE WAS FLUCTUATING. DURING TROUBLESHOOTING AFTER CRUISE POWER SET 103.4, THE NR 1,3, AND 4 PYLONS VALVES WOULD NOT CLOSE. WITH LT AND RT ISOLATION VALVES CLOSED, IT WAS DETERMINED THAT THE NR 1 PYLON VALVE WAS PARTIALLY OPEN WITH 8 PSI. THE NR 3 AND NR 4 INDICATED STUCK FULL OPEN WITH 38 PSI. APPROX 76.0 KG OF FUEL JETTISONED. NR 1,NR 3 AND NR 4 PYLON VALVES REPLACED AND ALL OPERATIONS NORMAL. ALSO NR 3 PRESSURE REGULATING VALVE REPLACED AND OPS CHECKED OK. WIRING CHECKS ALSO ACCOMPLISHED AND CHECKED OK. (K)