1. Modern Automotive Technology PowerPoint for by Russell Krick
Publisher The Goodheart-Willcox Co., Inc. Tinley Park, Illinois

2. Chapter 21
Fuel Tanks, Pumps,
Lines, and Filters

3. Contents
Fuel supply system
Fuel supply system service

4. 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

5. 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

6. 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

7. Fuel System Types

8. Fuel System Types

9. Fuel System Types

10. Fuel System Types

11. 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 backseat in a passenger car
Fuel tank capacity varies from about 12 to 25 U.S. gallons (45-95 liters)

12. 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

13. 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

14. 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

15. Fuel Tank Assembly

16. Thick steel bands bolt around the fuel tank
Fuel Tank Straps
Thick steel bands bolt around the fuel tank

17. 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

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

19. Fuel Gauge Operation

20. 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

21. 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

22. Fuel and emission control lines
Fuel Lines and Hoses
Fuel and emission control lines

23. 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

24. Plastic Fuel Lines Made of high-strength nylon tubing
Used instead of metal lines on some vehicles
Inside diameter determines line size when ordering parts
Quick-disconnect fittings are used to connect lines to injection components

25. 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

26. Returnless Fuel Injection Systems
Most late-model vehicles are equipped with returnless fuel injection systems
Some systems 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

27. Fuel Filters
Used to stop contaminants such as rust, water, and dirt from entering the fuel lines, hoses, throttle body, injectors, pressure regulator or any 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

28. Variations of Fuel Filters

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

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

31. Mechanical Pump Construction

32. Mechanical Pump Construction
Rocker arm
metal arm that pivots in the middle
the outer end of the rocker arm rides on the eccentric; the inner end of the arm operates the diaphragm
Return spring
keeps the rocker arm in contact with the eccentric

33. Mechanical Pump Construction
Diaphragm
synthetic rubber disc clamped between the halves of the pump body
metal pull rod connects the diaphragm to the rocker arm
Diaphragm spring
when compressed, the spring pushes on the diaphragm to produce fuel pressure and flow

34. Mechanical Pump Construction
Check valves
fuel flows easily through the valves in one direction but cannot flow through in the other direction
valves are situated so that fuel can enter through one valve and exit through the other

35. Pump Operation (Intake Stroke)
Eccentric lobe pushes on the rocker arm
Diaphragm is pulled down, compressing the diaphragm spring
Pumping chamber volume increases
Vacuum created allows atmospheric pressure to force fuel through the inlet check valve

36. Pump Operation (Intake Stroke)

37. Pump Operation (Output Stroke)
Eccentric lobe rotates away from the rocker arm
Diaphragm spring pushes on the diaphragm and pressurizes the fuel in the pumping chamber
Spring tension controls fuel pressure
Fuel flows out through the outlet check valve

38. Pump Operation (Output Stroke)

39. Pump Operation (Idling)
Occurs when the engine is running at slow speeds
The rocker arm is free to slide through the pull rod when fuel pressure compresses the diaphragm spring
The rocker arm moves up and down while the diaphragm remains stationary

40. Pump Operation (Idling)

41. 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

42. Vapor Lock

43. 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

44. In-Tank Electric Fuel Pumps

45. 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

46. Rotary Fuel Pumps There are three basic types of rotary fuel pumps:
impeller type
roller vane type
sliding vane type

47. Impeller Fuel Pump Uses centrifugal action to pump fuel
Uses a small dc motor to spin the impeller
Impeller blades cause the fuel to move outward due to centrifugal force
Centrifugal force produces pressure to move the fuel through the fuel lines

48. In-Tank Impeller Pump

49. Fuel hoses, pump motor, and strainer can be removed and replaced
In-Tank Impeller Pump
Fuel hoses, pump motor, and strainer can be removed and replaced

50. Roller-Vane Fuel Pump
Positive displacement pump that moves a specific amount of fuel with each rotation
Small rollers and an offset-mounted rotor disc produce fuel pressure
Positive displacement pumps require a pressure-relief valve to limit the output pressure of the pump

51. Roller-Vane Fuel Pump
When the rotor and rollers spin, they pull fuel in on one side of the pump
Fuel is trapped and pushed to a smaller area on the opposite side of the pump
This squeezes the fuel between the rollers, and the fuel is forced out under pressure

52. Roller-Vane Fuel Pump

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

54. Fuel Supply System
Service

55. 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

56. 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

57. Fuel Tank Removal
Empty the tank using the drain plug or by pumping the fuel out of the tank using an approved method
Special pumping systems with catch tanks are available
use extreme care because of the obvious fire hazard
do not use an incandescent trouble light, which could drop and break, lighting a fire

58. Fuel Tank Removal
A vehicle’s electric fuel pump may be used to empty the tank
disconnect the fuel hose at the main fuel line and route it into an approved gas can
turn the ignition key on and allow the fuel pump to force fuel from the tank to the can

59. Fuel Tank Removal
Draining the tank

60. Fuel Tank Removal After draining, remove the tank from the vehicle
Disconnect the filler neck, fuel lines, wires, and other components
Remove the straps or bolts holding the tank to the body
Slowly lower the tank without dropping or hitting it

61. Fuel Tank Installation
When installing a tank, replace the rubber insulators
Check that all fuel lines are properly secured
Replace the fuel in the tank
Check for leaks

62. Sending Unit Service
When a fuel gauge does not work properly, use a gauge tester before condemning the sending unit
If the gauge does not function with the tester installed, either the gauge or the circuit is faulty
If the gauge functions with the tester installed, replace the sending unit

63. Gauge tester connected to the harness
Sending Unit Service
Gauge tester connected to the harness

64. Using a cam tool to remove the cam lock ring
Sending Unit Service
Using a cam tool to remove the cam lock ring

65. A long drift punch and light hammer blows will rotate the lock ring
Sending Unit Service
A long drift punch and light hammer blows will rotate the lock ring

66. With the sending unit removed, measure its resistance
Sending Unit Service
With the sending unit removed, measure its resistance

67. 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

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

69. Fuel Line and Hose Service
To disconnect this fitting, press down on the locking tab while pulling apart

70. Fuel Line and Hose Service
To reconnect this fitting, simply push the two halves of the fitting together

71. Fuel Line and Hose Service
When installing fuel hoses, make sure they are pushed completely over raised areas on the fuel line

72. 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

73. Fuel Line and Hose Service Rules
Basic steps for making a new fuel line

74. 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

75. 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

76. 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

77. 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

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

79. 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 a faulty pressure relief valve or fuel pressure regulator

80. Fuel Pump Service Fuel pump noise
caused by bearing and part wear on electric pumps
caused by faulty rocker arm spring or rocker arm wear on a mechanical pump

81. Fuel Pump Service 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

82. Fuel Pump Tests There are three common fuel pump tests available:
fuel pump pressure test
fuel pump volume test
fuel pump vacuum test

83. Fuel Pump Tests
Several other problems can produce symptoms similar to those caused by a faulty fuel pump:
restricted fuel filters
damaged fuel lines or hoses
air leak in the vacuum side of the pump
injection or carburetor problems
ignition problems
engine mechanical problems (low compression)

84. 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

85. 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

86. 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)

87. 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

88. 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

89. Connect a vacuum gauge to the inlet side of the pump
Fuel Pump Vacuum Test
Connect a vacuum gauge to the inlet side of the pump

90. Fuel Pump Vacuum Test Activate the pump
With the pump running, compare the vacuum reading to specifications
General vacuum specifications:
7–10 in. Hg.
If the pump failed the pressure or volume tests but passed this test, the fuel supply lines or filters may be at fault

91. 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

92. Electric Fuel Pump Circuit

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

94. Supply Voltage Test
If supply voltage is low, use a service manual schematic to find problem areas

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

96. 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

97. Fuel Pump Removal and Replacement
To remove a mechanical pump, disconnect the fuel lines and unbolt the pump
Use a new gasket when installing a pump
Torque the fasteners to specifications

98. Fuel Pump Removal and Replacement

99. Fuel Pump Removal and Replacement
To remove an in-line electric pump, disconnect the fuel fittings and wires

100. 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

101. Fuel Pump Rebuilding
Older mechanical fuel pumps are held together with screws and can be overhauled if parts are available
Most mechanical and electric pumps are replaced, rather than rebuilt

102. Air Filter Service
An air filter removes dirt and dust from the air entering the engine intake manifold
Air filter service involves replacing or cleaning the filter element
Paper elements are usually replaced with a new unit

103. When replacing a filter element, wipe out the filter housing
Air Filter Service
When replacing a filter element, wipe out the filter housing

104. Air Filter Assembly