Fuel system.PPT

 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

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

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

Fuel System Types

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)

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

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

Fuel Tank Assembly
 Filler cap
 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

Fuel Tank Assembly

Fuel Tank Straps
Thick steel bands
bolt around
the fuel tank

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

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

Fuel Gauge Operation

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

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

Fuel and emission control lines

Fuel supply line, fuel return line, and fuel vapor line
are shown

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

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

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

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

Variations of
Fuel Filters

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

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

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

 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

 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

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

Pump Operation
(Intake Stroke)

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

Pump Operation
(Output Stroke)

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

Pump Operation
(Idling)

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

Vapor Lock

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

In-Tank Electric
Fuel Pumps

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

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

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

In-Tank Impeller Pump

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

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

 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

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

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

Air Filter Assembly

Fuel system.PPT

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Fuel system.PPT