Fuel Supply System Service Chapter 21 Lesson 2

Fuel Supply Systems Scanning Scan for diagnostic trouble codes before starting repairs Vehicles equipped with OBD II systems may monitor fuel tank pressure, fuel line pressure, fuel level, and other conditions Datastream operating values may be available for the circuit, which can speed troubleshooting

Fuel Tank Service Typical fuel tank problems include fuel leakage, physical damage, and contamination Vibration or rusting can cause a fuel tank to develop pinhole leaks

Fuel Tank Removal Empty the tank using the drain plug or by pumping the fuel out of the tank using an approved method Be sure to follow all Manufacture directions when removing or servicing the fuel tank and any other fuel system components.

Fuel Line and Hose Service Faulty fuel lines and hoses are common sources of fuel leaks Fuel hoses can become hard and brittle from exposure to engine heat and the environment Engine oil softens and swells hoses Metal lines should be replaced when smashed, kinked, rusted, or leaking

Fuel Line and Hose Service Inspect fuel lines, hoses, and fittings for leakage and damage

Fuel Line and Hose Service Rules Remember these rules when working with fuel lines and hoses: Place a shop rag around the fuel line fitting during removal Only use double-wall steel tubing Make smooth bends in tubing Form double-lap flares on the ends of the fuel line

Fuel Line and Hose Service Rules Reinstall all fuel line hold-down clamps and brackets Route all lines in their original location Use a recommended tool to release clip- type fittings If a plastic line or fitting is damaged, replace it Use OEM plastic tubing to repair fuel systems

Fuel Line and Hose Service Rules Avoid bending or rerouting stiff, used plastic lines Cover plastic fuel lines with a wet towel when welding, cutting, or grinding nearby Use approved synthetic rubber fuel hose in a fuel system

Fuel Line and Hose Service Rules Make sure a fuel hose fully covers its fitting or line before installing the clamps When servicing press-fit line fittings, you may need to replace the O-ring seal to prevent fuel leakage Double-check all fittings for leaks

Fuel Filter Service Involves periodic replacement or cleaning of system filters Clogged fuel filter can restrict flow to the injectors, diesel injection system, or carburetor Clogged in-tank strainer when clogged, the strainer can collapse and stop fuel flow the strainer will open again after the engine stalls

Fuel Pump Service Fuel pump problems include: low fuel pressure high fuel pressure fuel pump noise inadequate fuel flow fuel leakage

Fuel Pump Service Low fuel pump pressure High fuel pump pressure caused by worn components, high resistance in the electric pump circuit, or leaking check valves High fuel pump pressure caused by an faulty pressure relief valve or fuel pressure regulator

Fuel Pump Service Fuel pump noise Fuel pump leaks caused by bearing and part wear on electric pumps caused by faulty rocker arm spring or rocker arm wear on a mechanical pump Fuel pump leaks caused by diaphragm or gasket leaks on a mechanical pump inline electric fuel pumps often leak from inlet and outlet hoses leakage may contaminate the engine oil or leak externally

Fuel Pump Tests There are two common fuel pump tests preformed on systems using electric fuel pumps. fuel pump pressure test fuel pump volume test

Fuel Pump Pressure Test Connect a pressure gauge to the output line of the fuel pump fuel injected engines often have a service fitting on the fuel rail To test a mechanical pump, start the engine and allow it to idle To test an electric pump, you may need to activate the pump motor or start the engine

Fuel Pump Pressure Test Compare gauge readings to specifications If fuel pressure is not within specs, check the pressure regulator, pump volume, fuel lines, and filters before replacing the pump Isolate the fuel pressure regulator from the pump by restricting the return line If pressure rises sufficiently, the problem may be in the regulator

Fuel Pump Pressure Test General fuel pressure specifications: Gasoline injection fuel pressure 15–40 psi (100–280 kPa) Diesel supply pump pressure 6–10 psi (40–70 kPa) Carbureted engine fuel pressure 4–6 psi (30–40 kPa)

Route the output line from the fuel pump into a graduated container Fuel Pump Volume Test Route the output line from the fuel pump into a graduated container

Fuel Pump Volume Test With the pump running, allow fuel to pour into the container for the prescribed amount of time Close off the valve Compare the volume to specifications General volume specification: minimum of one pint (0.47 liters) in 30 seconds

Electric Fuel Pump Circuit Tests Many electric fuel pump problems are caused by electrical circuit problems Broken wires, faulty relays, shorts, blown fuses, computer malfunctions, and other problems can affect electric pump operation Follow a systematic step by step to diagnosing theses types of problems.

Supply Voltage Test If supply voltage is low, use a service manual schematic to find problem areas, by testing and eliminating fault free components

Electric Fuel Pump Circuit Tests Check the supply voltage at the Pump motor Energize and test the fuel pump relay. Replacing the relay with a known good relay may also be done.

Supply Voltage Test If a pump fails its performance tests, measure the supply voltage to the motor

Testing the Fuel Pump Relay Energize the relay and check continuity

Inertia Switch Used to open the fuel pump circuit after a severe impact or collision Safety device that can prevent a serious fire by shutting off the pump in a collision Usually located in the trunk or near the electric fuel pump After a collision, a button on the switch must be pressed to reset the switch and enable the pump

Fuel Pump Removal and Replacement To remove an in-tank electric pump, the fuel tank must often be removed from the vehicle Some vehicles are equipped with a fuel pump access door in the trunk or under the rear seat the access door allows pump removal and replacement without tank removal