Fuel Pump: Description and Operation

DESCRIPTION

This vehicle uses a saddle type tank a reservoir on both sides of the rear drive shaft. The fuel pump is in the module on the driver side of the vehicle and the fuel pressure regulator is in the module on the passenger side of vehicle. The fuel outlet is on the passenger side and supplies fuel to the engine. The fitting on the fuel pump module (Driver side) is a vapor line fiffing that connects to the passenger side module. Both modules have fuel level sending cards. There are 2 hoses that connect the modules together one is the fuel supply line the other is a return or siphon hose. The lines are removed from the fuel pump module when servicing either unit. The ORVR (Onboard Refueling Vapor Recovery) control valve is in the passenger side module.


















OPERATION

The way the pump works is as follows fuel enters the reservoir of the driver side module. The fuel pump pumps the fuel through the filter to the passenger side module through a supply line inside tank. The pressure regulator inside the passenger side module regulates the pressure at 58 psi. All unused fuel that is not sent to the engine is fed through a venturi at the bottom of the passenger side module. This creates a low pressure siphoning effect and draws fuel from the passenger side of the tank and transfers it to the drivers side tank via siphon hose inside the tank. While the vehicle is running the fuel in the passenger side of tank is continuously transferred to the drivers side. Fuel will continue to fill the drivers side tank till it reaches the bridge section and then start to spill over to the passenger side.

As stated above we have two fuel level senders the reading of these senders are averaged out to give us the fuel gauge reading. When we are diagnosing a sender concern the passenger side reading should never be higher than the Drivers side reading. It is possible depending on fuel level and driving habit before diagnosing~ to spill fuel over to the passenger side that might indeed show a lower resistance value than the driver side.

The fuel gauge gives an indication to the vehicle operator of the level of fuel in the fuel tank. This gauge is controlled by the instrument cluster circuit board based upon cluster programming and a hard wired input received by the cluster from the fuel level sending units on the modules in the fuel tank.

The instrument cluster continually monitors the fuel tank sending units to determine the level of fuel in the fuel tank. The cluster then sends the proper fuel level messages to other electronic modules in the vehicle over the Controller Area Network (CAN) data bus. For further diagnosis of the fuel gauge or the instrument cluster circuitry that controls the gauge (Refer ELECTRICAL/INSTRUMENT CLUSTER - DIAGNOSIS AND TESTING). The fuel gauge is serviced as a unit with the instrument cluster.

The tech needs to order the correct part when replacing the senders modules and tank as all are able to be replaced individually.