1. Fuel Supply System
Chapter Lesson 1

2. Fuel Supply System
Draws fuel from the fuel tank and forces it into the fuel metering device
Fuel metering devices fed by the fuel supply system include:
gasoline injection system
diesel injection system
carburetor

3. Fuel Supply System Components
The basic parts of a fuel supply system include:
Fuel tank
stores gasoline, diesel fuel, or alternate fuel
Fuel lines
carry fuel between the tank and the fuel metering system

4. Fuel Supply System Components
Fuel pump
draws fuel from the tank and pumps it to the fuel metering system
Fuel filters
remove contaminants in the fuel

5. Fuel Tank
Must safely hold an adequate supply of fuel for prolonged engine operation
Normally mounted in the rear of the vehicle
under the trunk or back seat in a passenger car
Fuel tank capacity varies from about 12 to 25 U.S. gallons (45-95 liters)

6. Fuel Tank Construction
Fuel tanks are made of either thin sheet metal or plastic
Metal tanks are made by soldering or welding two formed pieces of sheet metal together
a zinc alloy is plated to the sheet metal to keep the tank from rusting

7. Fuel Tank Assembly
Several components go together to make up the fuel tank assembly:
Fuel tank filler neck
extension tube on the tank for filling the tank with fuel
Spillback ball
large ball in the fuel tank filler neck to prevent fuel from leaking out of the vehicle during fillups

8. Fuel Tank Assembly Filler cap Fuel tank baffles Fuel tank straps
sealed to prevent the escape of fuel and fuel vapors from the tank
cap is not vented to atmosphere
Fuel tank baffles
placed inside the tank to keep fuel from sloshing
Fuel tank straps
used to secure the tank to the vehicle

9. Fuel Tank Assembly

10. Tank Pickup-Sending Unit
Extends down into the tank to draw fuel and operate the fuel gauge
Sending unit is a variable resistor
resistance changes with changes in the fuel level
controls the amount of current reaching the fuel gauge

11. Tank Pickup-Sending Unit
“Sock” filter strains out debris in tank

12. Fuel Gauge Operation

13. Fuel Tank Pressure Sensor
Used to monitor the fuel tank pressure in late-model vehicles equipped with OBD II systems
Aids in the operation of the evaporative emissions control system

14. Fuel Lines and Hoses Carry fuel from the tank to the engine
Fuel lines are made of strong double-wall steel tubing
Fuel hoses are made of synthetic rubber
needed where movement occurs between parts, such as between the frame and the engine

15. Fuel Lines and Hoses Will cover in more detail in chapter 43
Fuel and emission control lines

16. Fuel supply line, fuel return line, and fuel vapor line are shown
Fuel Lines and Hoses
Fuel supply line, fuel return line, and fuel vapor line are shown

17. Fuel Return System
Most fuel injected vehicles use a fuel return system to cool fuel and prevent vapor lock
Fuel return line carries excess fuel back to the tank
keeps cool fuel constantly flowing through the system

18. Returnless Fuel Injection Systems
Some late-model vehicles do not have fuel return lines
These vehicles use a pressure regulator mounted on the electric fuel pump assembly (in the fuel tank)
When system pressure exceeds specifications, the regulator routes fuel back to the tank

19. Fuel Filters
Used to stop contaminants such as rust, water, and dirt from entering the fuel lines, hoses, throttle body, injectors, pressure regulator or an other part that could be damaged
“Sock” filter on the tank pickup tube is used to filter out debris
Second filter is usually located in the main fuel line

20. Variations of Fuel Filters

21. Vapor Lock
Problem created when bubbles in overheated fuel reduce or stop fuel flow
Fuel boils, forming bubbles that displace liquid fuel
Fuel bubbles reduce fuel pump output, causing engine performance problems
Caused by high underhood temperatures and low fuel pressures

22. Vapor Lock

23. Fuel Pumps There are two basic types of fuel pumps:
mechanical fuel pump
electric fuel pump

24. Mechanical Fuel Pump Powered by an eccentric on the engine camshaft
Bolts to the side of the engine block
Used on carbureted gasoline engines

25. Electric Fuel Pump
Produces fuel pressure and flow for the fuel metering section of a fuel system
Located inside the fuel tank or in the fuel line between the tank and the engine
A few systems use a pump in the tank and a second pump in the line to further increase fuel pressure

26. In-Tank Electric Fuel Pumps

27. Electric Fuel Pump Advantages
Produces almost instant pressure
Produces smoother flow than a mechanical pump
Vapor lock is less likely because the pump is located away from the engine and pressurizes all the fuel lines that are near engine heat
high pressure increases the boiling point of fuel

28. Electric Pump Circuit
In this circuit, if the oil pressure drops too low, the switch shuts off the fuel pump