1. Fuel Supply System Service
Chapter Lesson 2

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

3. 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

4. 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.

5. 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

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

7. 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

8. 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

9. 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

10. 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

11. 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

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

13. 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

14. 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

15. 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

16. 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

17. 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

18. 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)

19. 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

20. 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

21. 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.

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

23. 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.

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

25. Testing the Fuel Pump Relay
Energize the relay and check continuity

26. 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

27. 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