THIS IS NOT A SAFETY RECALL IN ACCORDANCE WITH THE SAFETY ACT. HOWEVER, IT IS DEEMED A SAFETY IMPROVEMENT CAMPAIGN BY THE AGENCY. VEHICLE DESCRIPTION: 1990-1993 FORD F-SERIES VEHICLES EQUIPPED WITH DUAL FUEL TANKS AND 4.9, 5.0,5.8, OR 7.5 LITER GASOLINE FUELED ENGINES. SOME VEHICLES CAN EXPERIENCE A CROSS TANK FUEL FLOW CONDITION DUE TO A DAMAGED CHECK VALVE IN THE FUEL PUMP/SENDER ASSEMBLY. FUEL MAY BE SUPPLIED FROM ONE TANK AND SOME OR ALL OF THE UNUSED FUEL MAY BE RETURNED TO THE OTHER TANK.