Gasoline fuel supply systems

Function: store, transport, Pressurize and filter gasoline going to carburetor

or fuel injection system.

Vocabulary

1. Fuel tank 9.)intake manifold vacuum

2. Baffles 10.)vaporization

3. Coating

4. Pick up tube and filter

5. Condensation

6. Fuel filter

7. Mechanical fuel pump

8. Variable resistance unit

A Complete vehicle fuel system

Fuel tank

• Made of sheet steel or plastic• Zink (Galvanized) coating to prevent corrosion.• Baffles are add for strength, prevent sloshing

and production of fuel vapors & to keep float level more constant.

• Do not attempt to “Drop” and repair your own fuel tank or in tank pump until you have had the proper training.

• Never weld a fuel tank.

Typical Fuel Tank

Fuel lines

• Hard fuel lines are steel or plastic & run from tank to engine compartment.

• Soft lines connect from hard line to engine fuel system or from tank to hard lines

• Top line is low pressue, Bottom line is high pressure.

Typical low pressure Fuel Filters

• Middle : In-line type. Location : on pressure side of fuel line between pump and carburetor.

• Top: In carburetor type . Typical GM.

• Bottom: screw in “ford” external carb type.

• Filters must be installed in the correct direction.

Typical in-carb fuel filter

High pressure Fuel Filters

• Located under car on frame or in engine compartment on pressure side of pump.

• Body is metal. • Use computer

component locater to find filter or follow fuel lines from tank to injection system.

Replacement Interval

• 30 to 50,000 miles

• Replacing filter more often may help pump to last longer.

• Special tools may be needed to remove and replace some filters.

• Relieve system pressure before removing filter. (See slide # 30)

• Do not spill gasoline!!! And no sparks .

Fuel Pumps• Mechanical Fuel

pumps• 3 to 7 psi• Run’s off camshaft

eccentric. • Located on side of

engine.• Leak in diaphragm

will lead to drop in pressure & fuel in oil.

• Electric Fuel pump• 15 to 60 psi• Typically Located in

fuel tank.• Relay used to control

electricity to pump.• Relay controlled

through PCM • Oil pressure & inertia

switch are often used.

Mechanical Fuel pumps

• The float level in the carburetor determines how much fuel will flow through the fuel pump.

Mechanical Fuel pump

Typical mechanical Fuel Pump

A weak mechanical fuel pump can cause a vapor lock condition.

Typical Electric fuel Pumps

Electric fuel pump

In – Tank electric fuel pump

• The pump will often be combined with the fuel gauge sending unit and vapor recovery system. This assembly is very expensive to replace!

Fuel pump relays

• Use low current to switch a higher current.

• All Electric fuel pumps use a relay.

• Most often are controlled by the vehicles PCM , an oil pressure sensor and an Inertia switch.

• Relay is common source of fuel pump not going on.

• Use component locater to find relay.

Fuel Pump Relay circuit

Fuel pump relay

Fuel gauge sending unit

• The fuel Gauge sending unit sends a variable voltage signal to the fuel gauge. It does this using a variable resister attached to a float in the fuel tank.

Fuel System part 2

• Testing the fuel system

Fuel Tank Caps

• Fuel Tank Caps come in vented and non-vented types.

• Only Non – vented caps can be used on vehicles built with vapor recovery systems.

• Leaking Fuel caps are the # 1 cause of activated check engine lights.

A Fuel Cap tester

Vapor Recovery Systems• All modern vehicles must have a Vehicle vapor

recovery system. This system uses a canister filled with charcoal and other filters to store fuel vapors from the fuel tank and carburetor. During part throttle these fuel vapors are “purged” to the intake manifold. This is done with a thermo – vacuum valve on older cars and with a computer controlled “purge valve on newer cars.

Fuel pressure regulators

• Fuel pressure regulators control the pressure of the fuel going to the injectors or carburetor.

Testing the fuel supply system

• The most common test for the fuel supply system is the pressure / volume test .

• This test will check for both fuel system pressure and volume.

• Both low pressure (carb type) and high pressure ( EFI ) can be tested.

Low pressure tester

• Gauge must be connected inline between the fuel pump and the carburetor. (You must tap into the incoming line)

• 3 to 7 psi• 1 quart per minute

High pressure test equipment

• Gauge must be capable of measuring pressures typical in EFI systems.

• 15 to 60 psi typical• Must tap into in-

coming fuel line (difficult) or fuel rail test port.

Typical EFI test ports

On unit test:

• Fuel tank • Fuel lines• Fuel pumps• Vapor recovery system• Fuel gauge sending unit• Fuel pump Relays• Fuel caps must seal• Testing fuel supply systems