Fuel Gauge

The pointer of the Fuel Gage is moved by the magnetic fields of two coils. The coils are at right angles to each other. Battery voltage is applied to the E-Coil (empty) and the circuit divides at the opposite end of the coil. One path continues to ground through the F-Coil (full). Another goes to ground through the variable resistance of the level sensor in the Fuel Pump and Sender (Gasoline) or Fuel Gage Sender (Diesel) for vehicles with single fuel tanks. The Fuel Pump Balance Module averages the resistance for vehicles with two fuel tanks. When the tank is low, the resistance of the level sensor is low. A large current flow passes through the E-Coil and the pointer moves toward E on the Fuel Gage. When the tank is full, the level sensor's resistance is high. Less current passes though the E-Coil and the pointer moves toward F on the scale. With two coils operating the pointer, the Fuel Gage is not affected by changes in the system's battery voltage. For vehicles with single fuel tanks, the level sensor in the Fuel Sender produces a resistance of about 4 ohms when the tank is empty. The resistance is about 90 ohms when the tank is full. A short to ground in the sender or wiring will provide a fully empty indication. An open in the circuit will produce a fully-full indication. For vehicles with dual fuel tanks, the Fuel Pump Balance Module measures the resistance of both Fuel Senders. The module averages the resistance and produces an equivalent resistance reflecting the average level of both fuel tanks. Both power to the module and a change in the input resistance are required to produce a change in the output resistance to the Fuel Gage. The Fuel Pump Balance Module responds to a very low resistance (short to ground) in one or both fuel sender circuits by considering the affected tank(s) to be empty. A very high resistance (open circuit) in either fuel sender circuit will cause the Fuel Pump Balance Module to produce a zero output (both tanks empty) signal to the Fuel Gage. The Fuel Pump Balance Module equalizes level in the two fuel tanks. Fuel is fed to the Engine from the front (primary) fuel tank. When the level in the front tank decreases to about two gallons less than the level in the rear (secondary) fuel tank, the Fuel Pump Balance Module energizes the Fuel Pump Balance Relay. This starts the Balance Fuel Pump which transfers fuel from the rear tank to the front tank. When the level in the front tank increases to about two gallons greater than the rear tank, the Balance Fuel Pump stopped. This approach tends to empty the rear tank first.