ISSUE Some 2004-2008 F-Super Duty 650-750 vehicles equipped with dual fuel tanks, may exhibit one tank emptying and the other tank remaining full. ACTION Follow the Service Procedure steps to correct the condition. SERVICE PROCEDURE On 2004-2007 F-Super Duty 650-750 vehicles the right fuel tank will be empty and fuel does not transfer from the left tank. On 2008 F-Super Duty 650-750 vehicles the left fuel tank will be empty and fuel does not transfer from the right tank.
Transfer pump diagnostics note both sending units provide input to the fuel transfer pump (module). Only one sender is also wired to the instrument cluster. The integral module in the transfer pump controls the transfer pump operation. Note on 2004-2007 model year vehicles only the right sender provides fuel level information to the cluster/gauge and the fuel transfer pump (module). The right tank feeds the engine fuel system while the left tank feeds only the right tank to maintain equal fuel levels. Note on 2008 model year vehicles the left sender provides fuel level information to the cluster/gauge and fuel transfer pump (module). The left tank feeds the engine fuel system while the right tank feeds only the left tank to maintain equal fuel levels.
Refer to Wiring Diagram Section 49 for the following diagnostics. At Connector C3264 (2005-2008), C9102a (2004), located at the fuel transfer pump, perform the following: 1. Verify the voltage on pin-E (pk/bk wire) is battery voltage. If concern is found, repair as necessary and reevaluate transfer pump operation. 2. Verify pin-D (bk/og wire) has a good ground. If concern is found, repair as necessary and reevaluate transfer pump operation. 3. Verify the resistance on both sending units pin-A and pin-B are within the range of 15 Ohms empty to 160 Ohms full. If concern is found, repair as necessary and reevaluate transfer pump operation. 4. With all the connectors connected and the key on engine running (KOER), verify the voltage at alternator (circuit 1818) is 7-7.5 volts. If voltage is outside this range, load test circuit 1818 (wh/bk wire) to ensure wire integrity. If circuit 1818 integrity is verified, and voltage is below the specified range, replace alternator. Refer to Workshop Manual (WSM), Section 414-02. 5. If no concerns are found with voltage/resistance in steps 1-4, replace the fuel transfer pump. Refer to WSM, Section 310-01. 6. Verify transfer pump operation by creating a 10 gallon fuel difference, with the right side tank level on 2004-2007 model year and left side tank on 2008 model year being lower. Start the engine and observe fuel transfer pump operation.