AN MD80 PILOT REPORTS A FUEL BOOST PUMP FAILED IN A TANK WITH AN OPERATING QTY GAUGE WHILE THE TANK WITH THE INOP QTY GAUGE IS FUELING BOTH ENGS. EMER DECLARED WITH A DIVERSION TO THE NEAREST ARPT.

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TOOK OFF WITH MEL: RIGHT FUEL QUANTITY INOP. AT CRUISE AFTER FUEL IN CENTER TANK DEPLETED; CROSSED CHECKED FUEL BURN AND QUANTITY IN LEFT TANK; READ 9300 LBS. WHEN LEFT TANK GETS TO 8000 LBS; THE QUANTITY INDICATOR STOPS BUT THE FUEL USED CONTINUE. INDICATING THAT WE WERE BURNING FROM THE RIGHT TANK AND THAT GAUGE IS INOP. CALCULATING THE FUEL BURNED AGAINST THE FUEL USED MINUS THE LEFT TANK FUEL THAT WE COULD NOT GET; IT WAS ESTIMATED THAT WE HAD ABOUT 40 MINUTES OF USEABLE FUEL. ACTIONS TAKEN: CHECKED THE BOOST PUMPS ON -FUEL HEAT -CHECKLIST FOR FUEL QUANTITY INDICATOR -ABNORMAL TEST -CHECKLIST FOR FUEL LEAK/ABNORMAL FUEL USAGE. HERE THE CHECKLIST CALLS FOR TURNING OFF THE BOOST PUMPS ON THE RIGHT ENGINE. I CHOSE NOT TO EXERCISE THIS BECAUSE OF THE WEATHER; TURB; CLOUDS; AND NOT WANTING TO BE IN A POSITION OF A FLAMEOUT. HAD DISPATCH ON THE RADIO. EVERYONE AGREES WE NEED TO LAND AS SOON AS POSSIBLE. ZZZ WAS THE CLOSEST AND BEST AIRFIELD. DECLARED THE EMERGENCY WITH ATC. PROCEED TO ZZZ. IT TOOK 4 1/2 DEGREES ON RIGHT AILERON TRIM TO HOLD HEADING. UNEVENTFUL OTHERWISE. WE DID NOT GET A FUEL LEVEL LOW LIGHT BUT MAINT CONFIRMED THAT WE WERE BELOW 2500 LBS IN THE RIGHT TANK. NOT SURE. WOULD LIKE TO KNOW WHAT MAINT FINDS WITH AIRCRAFT AND A LOOK AT THE FUEL LEAK/ABNORMAL FUEL USAGE CHECKLIST WHICH CALL FOR TURNING OFF THE BOOST PUMPS ON WHAT COULD BE YOUR GOOD ENGINE.CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED THAT HE HAD NOT BEEN TOLD BY HIS ACR MAINT WHAT THE MALFUNCTION WAS.