Checking the Fuel Tank Sender Unit Calibration

WARNING:
Observe all fire and safety precautions described in Section 5.1.2 of the XJ6-XJ12 Vehicle Service Manual when working on the fuel system.

1. Ensure that the vehicle is standing on a level surface in a normal attitude with no excessive loads in the passenger or luggage compartments.

2. If possible, the tank should contain 2.6-4.0 gallons (10-15 liters) of fuel when beginning the diagnostic procedure. This amount corresponds to a fuel gauge indication between E and 1/4 full. The low fuel warning lamp should be OFF

3. With the ignition OFF, disconnect both wires at the sender unit.

4. Connect a multimeter, set to 0-1000 ohm resistance range, to the terminals of the sender unit.

5. Using a suitable pump and container, pump fuel out of the vehicle's tank until the fuel tank is empty. The meter reading should increase during this process to more than 900 ohms.

6. Slowly add fuel (approximately 1.6 gallons [6 liters]) to the tank until the meter reading is 900 ohms +/- 18 ohms. The process must be done as accurately as possible since it creates the base line for the remaining steps in the procedure.

7. Disconnect the multimeter and reconnect the vehicle wiring to the sender unit. Turn the ignition ON. The gauge should now show empty with the low fuel level lamp ON. Turn the ignition OFF.

8. Measure 1.1 gallons (4 liters) of fuel into the vehicle fuel tank using a funnel to avoid spillage. Use an accurate means to measure the fuel.

The fuel tank now contains 2.6 gallons (10 liters) from empty.

9. Disconnect the vehicle wiring from the sender. Reconnect the multimeter and check that reading is 735 ohms maximum. If the reading is greater than 735 ohms, add a maximum of 0.3 gallon (1 liter) of fuel. The reading should now be 735 ohms or less. Reconnect the wiring and check that the low fuel level warning light is OFF with the ignition ON.

If the low fuel level warning light remains ON with a reading of 735 ohms or slightly less, the sender unit is not defective. If an incorrect warning lamp indication is the only fault found, interrogate the instrument pack using the PDU in the Diagnostic Mode.

10. Add 2.6 gallons (10 liters) of fuel to the tank. The gauge should now indicate approximately 1/4 full.

The fuel tank now contains 5.3 gallons (20 liters) from empty.

11. Add another 5.3 gallons (20 liters). The gauge should now indicate approximately 1/2 full.

The fuel tank now contains 10.6 gallons (40 liters) from empty.

12. Add another 5.3 gallons (20 liters). The gauge should now indicate approximately 3/4 full.

The fuel tank now contains 15.9 gallons (60 liters) from empty.

13. Add another 5.3 gallons (20 liters). The gauge should now indicate full. The fuel tank now contains 21.1 gallons (80 liters) from empty.

If the fuel tank accepts more than 21.1 gallons (80 liters), continue filling until no more fuel is accepted. The specified capacity of the tank is 21.4 gallons (81 liters) from "run dry". The total amount that was added from step 8 above, indicates whether the tank is now actually full, and whether the 1.6 gallons (6 liters) from empty point was accurately achieved in step 6.

14. If fuel filling facilities are not available on the same premises, an accurate allowance must be made in the procedure for fuel consumed while traveling between the gas station and the workshop. Where appropriate, fuel should be added to compensate before resistance measurements are made.