What was found
DURING CLIMB OUT, CENTER FUEL PRESSURE LOW ILLUMINATE WITH APROXIMATELLY 2000 LBS, IN THE CENTER TANK. WHILE EXECUTING THE QHR PROCEDURE THE CENTER FUEL QUANTITY INITIALLY INCREASED TO 2500 LBS , AT THE POINT THE LOW PRESS LIGHT EXTINGUISHED AND FUEL RETURNED NORMALLY FOR SEVERAL MINUTES. AT THAT POINT THE LIGHT REILLUMINATED. AN EMERGENCY WAS DECLAED AND THE FLIGHT AIR INTERRUPTED BACK TO ORD FOR LANDING WITH NO FURDER INCIDENT. NOTE: WHILE CENTER FUEL QUANTITY WAS INCREASING BOTH MAIN TANK QUANTITIES WERE DECREASING. REPLACED CENTER TANK EXTRACTOR CHECK VALVE PER AMM 28-20-26. NO DISCREPANCIES NOTED. AFTER CLOSE CLEARANCE, PANEL 1436C SEALED AT 2230. OK FOR SERVICE. THE AIRCRAFT WAS GROUNDED.