start
Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition
By James D. Halderman

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2009Pearson
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OBJECTIVES:
After studying Chapter 58, the reader should
be able to:

•

•

Prepare for ASE Engine Performance (A8)
certification test content area “C” (Fuel, Air
Induction, and Exhaust Systems Diagnosis and

Repair).
Describe how to check an electric fuel pump
for proper pressure and volume delivery.

Continued
Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition
By James D. Halderman

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OBJECTIVES:
After studying Chapter 58, the reader should
be able to:

•
•

•

Explain how to check a fuel-pressure
regulator.
Describe how to test fuel injectors.
Explain how to diagnose electronic fuelinjection problems.

Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition
By James D. Halderman

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KEY TERMS:
accumulator • baffle • check valve • delivery system
filter basket • gerotor • hydrokinetic pump • inertia switch
onboard refueling vapor recovery (ORVR)

peripheral pump
residual or rest pressure • roller cell • rotary vane pump
side-channel pump • turbine pump
vacuum lock • vapor lock • volatile organic compound
(VOC)
Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition
By James D. Halderman

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FUEL DELIVERY SYSTEM
Creating and maintaining a correct air–fuel mixture requires a 
properly functioning fuel and air delivery system. Fuel delivery 
(and return) systems use many if not all of the following 
components to make certain that fuel is available under the right 
conditions to the fuel­injection system:

Fuel storage tank, filler neck, and gas cap
Fuel tank pressure sensor
Fuel pump
Fuel filter(s)
Fuel delivery lines and fuel rail
Fuel­pressure regulator
Fuel return line
Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition
By James D. Halderman

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FUEL TANK
A vehicle fuel tank is made of steel or polyethylene plastic. Some 
SUVs and light trucks have an auxiliary fuel tank.
Tank design and capacity are a compromise between available 

space, filler location, fuel expansion room, and fuel movement.
Some later­model tanks deliberately limit tank capacity by 
extending the filler tube neck into the tank low enough to prevent 
complete filling, or by providing for expansion room.
A vertical baffle in this same tank limits fuel sloshing as the vehicle 
moves.
See Figure 58–1. 
Continued
Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition
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Figure 58–1 A typical fuel tank installation.

Continued

Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition
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Regardless of size and shape, all fuel tanks incorporate most if not 
all of the following features:

Inlet or filler tube through which fuel enters the tank
Filler cap with pressure holding and relief features
An outlet to the fuel line leading to the fuel pump or fuel 
injector
Fuel pump mounted within the tank
Tank vent system
Fuel pickup tube and fuel level sending unit


Continued
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Tank Location and Mounting  Most vehicles use a horizontally 
suspended fuel tank, usually mounted below the rear of the floor 
pan, just ahead of or behind the rear axle.
Fuel tanks are located there so that frame rails and body 
components protect the tank in the event of a crash. Fuel inlet 
location depends on the tank design and filler tube placement. It 
is located behind a filler cap and often a hinged door in the outer 
side of either rear fender panel.
Generally, a pair of metal retaining straps holds a fuel tank in 
place. Underbody brackets or support panels hold the strap ends 

using bolts. To prevent squeaks, some models have insulated 
strips cemented on the top or sides of the tank wherever it 
contacts the underbody.
Continued
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Filler Tubes  Large tube extending from the tank to an opening on 
the outside of the vehicle. 
Figure 58–2
A three-piece filler tube assembly.

Federal authorities recognized methanol as a poison, and methanol 
used in gasoline is a definite health hazard. Additionally, gasoline 

is a suspected carcinogen (cancer­causing agent). 

Continued
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To prevent siphoning, manufacturers welded a filler­neck check­
ball tube in fuel tanks. To drain check­ball­equipped fuel tanks,
a tech must disconnect the check­ball tube at the tank and attach a 
siphon directly to the tank. 

Figure 58–3 A view of a typical filler
tube with the fuel tank removed.
Notice the ground strap used to

help prevent the buildup of static
electricity as the fuel flows into the
plastic tank. The check ball looks
exactly like a ping-pong ball.

Continued
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Onboard refueling vapor recovery (ORVR)  systems reduce 
evaporative emissions during refueling by adding components to 
filler neck and tank.
One system utilizes a tapered filler neck with a smaller diameter 
tube and a check valve. When fuel flows down the neck, it opens the 

normally closed check valve. The vapor passage to the charcoal 
canister is opened. The decreased size neck and the opened air 
passage allow fuel and vapor to flow rapidly into the tank and the 
Figure 58–4 Vehicles equipped with onboard
canister respectively. 
When the fuel has reached a 
predetermined level, the 
nozzle shuts off, preventing 
the tank from being 
overfilled.

refueling vapor recovery usually have a reducedsize fill tube.

Continued
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Pressure­Vacuum Filler Cap Fuel and vapors are sealed in the 
tank by the safety filler cap.
The safety cap must release excess pressure or excess vacuum. 
Either condition could cause fuel tank damage, fuel spills, and 
vapor escape. Typically, the cap will release if the pressure is
over 1.5 to 2.0 psi (10 to 14 kPa) or if the vacuum is 0.15 to 
0.30 psi (1 to 2 kPa).

Continued
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Fuel Pickup Tube The fuel pickup tube is usually a part of the fuel 
sender assembly or the electric fuel pump assembly. 
Figure 58–5 The fuel pickup tube is part of
the fuel sender and pump assembly.

As dirt and sediment gather
on the bottom of a fuel tank, 
the pickup tube is fitted with
a filter sock or strainer to 
prevent contamination from 
entering the fuel lines. 
The strainer also acts as a 
water separator and the filter 
sock is designed to filter out 
particles that are larger than 70 
to 100 microns, or 30 microns 
if a gerotor­type fuel pump is 
used. 
Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition
By James D. Halderman

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Tank Venting Requirements  Fuel tanks must be vented to prevent 
a vacuum lock as fuel is drawn from the tank. Without a vent, the 
air pressure inside the tank would drop below atmospheric pressure, 
developing a vacuum which prevents the flow of fuel. Under 
extreme pressure variance, the tank could collapse. 
An EVAP system vents gasoline vapors from the fuel tank to a 
charcoal­filled vapor storage canister, and uses an unvented filler 
cap. Many filler caps contain valves that open to relieve pressure or 
vacuum above specified levels. Systems that use completely sealed 
caps have separate pressure and vacuum relief valves for venting.
Because fuel tanks are not vented directly to the atmosphere, the 
tank must allow for fuel expansion, contraction, and overflow. One 
way is to use a dome in the top of the tank. GM uses a design with a 
vertical slosh baffle reserving room for fuel expansion.
Continued

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By James D. Halderman

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Rollover Leakage Protection  All vehicles have devices to prevent 
fuel leaks in vehicle rollover or a collision in which
fuel may spill.
Variations of the one­way check valve may be installed between
the fuel tank and the engine. The valve may be installed in the fuel 
return line, vapor vent line, or fuel tank filler cap.
In addition to the rollover protection devices, some vehicles use 
devices to ensure that the fuel pump shuts off when an accident 
occurs. Some pumps depend upon an oil pressure or an engine speed 
signal to continue operating; some air vane sensors use microswitch 
is built into the sensor.
See Figure 58–6.
Continued
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Figure 58–6 On some vehicles equipped with an airflow sensor, a switch is used to energize
the fuel pump. In the event of a collision, the switch opens and the fuel flow stops.

Continued
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Ford vehicles use an inertia switch installed in the rear of the 
vehicle between the electric fuel pump and its power supply. With 
any sudden impact, such as a jolt from another vehicle, the inertia 
switch opens and shuts off power to the fuel pump. The switch must 
be reset manually by pushing a button to restore pump current.

Figure 58–7
Ford uses an inertia
switch to turn off the
electric fuel pump in
an accident.

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FUEL LINES
Fuel and vapor lines supply fuel to the throttle body or fuel rail, and 
are made of steel, nylon tubing, or fuel­resistant rubber hoses. They 
also return excess fuel and vapors to the tank. Depending on their 
function, fuel and vapor lines may be either rigid or flexible.

Fuel lines must remain as cool to prevent vaporizing the gasoline 
and causing vapor lock. When this happens, the fuel pump 
supplies only vapor that passes into the injectors. Without liquid 
gasoline, the engine stalls and a hot restart problem develops.
The fuel delivery system supplies 10 to 15 psi (69 to 103 kPa) or up 
to 35 psi (241 kPa) to many throttle­body injection units and up to 
50 psi (345 kPa) for multiport fuel­injection systems. Higher­
pressure systems such as these require special fuel lines.
Continued
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Rigid Lines  All fuel lines fastened to the body, frame, or engine 
are made of seamless steel tubing. Steel springs may be wound 
around the tubing at certain points to protect against impact 
damage.
Only steel tubing, or that recommended by the manufacturer, 
should be used when replacing rigid fuel lines.
Never substitute copper or aluminum tubing for steel tubing. 
These materials do not withstand normal vehicle vibration and 
could combine with the fuel to cause a chemical reaction.

Continued
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Flexible Lines  Most fuel systems use synthetic rubber hose 
sections where flexibility is needed. Short hose sections often 
connect steel fuel lines to other system components.
The fuel delivery hose inside diameter (ID) is generally larger 
(3/16 to 3/8 inches or 8 to 10 millimeters) than the fuel return
hose ID (1/4 inches or6 millimeters).
Fuel­injection systems require special­composition reinforced 
hoses specifically made for these higher­pressure systems.
Vapor vent lines must be made of materials that resist fuel vapors. 
Replacement vent hoses are usually marked with the designation 
“EVAP” to indicate their intended use.
Continued
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Fuel Line Mounting  Fuel supply lines from the tank to a throttle body 
or fuel rail are routed to follow the frame along the underbody of the 
vehicle. 

Vapor and return lines 
may be routed with the 
fuel supply line. 
All rigid lines are 
fastened to the frame 
rail or underbody 
with screws and 
clamps, or clips. 

Continued


Figure 58–8 Fuel lines are routed along the frame or
body and secured with clips.

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Fuel­Injection Lines and Clamps  Hoses used for fuel­injection 
systems are made of materials with high resistance to oxidation 
and deterioration.
Replacement hoses for injection systems should always be 
equivalent to original equipment manufacturer (OEM) hoses.
Screw­type clamps are essential on injected engines and should 
have rolled edges to prevent hose damage.
CAUTION: Do not use spring­type clamps on fuel­injected engines—

they cannot withstand the fuel pressures involved.

Continued
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Fuel­Injection Fittings and Nylon Lines  Because of operating 
pressures, fuel­injection systems use special kinds of fittings to 
ensure leakproof connections.
Some high­pressure fittings on GM and other manufacturer’s 
vehicles with port fuel­injection systems use O­ring seals instead 
of the traditional flare connections. When disconnecting, inspect 
the O­ring for damage and replace it if necessary. Always tighten 
O­ring fittings to the specified torque value to prevent damage.

O­rings are made of special materials that withstand contact with 
gasoline and oxygenated fuel blends. Some manufacturers specify 
that O­rings be replaced every time the fuel system connection is 
opened, with a new part specifically designed for fuel system use.
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Ford also uses spring­lock connectors to join male and female ends 
of steel tubing.The coupling is held together by a garter spring 
inside a circular cage. 
The flared end of the 
female fitting slips 
behind the spring to 

lock the coupling 
together.
Figure 58–9 Some Ford metal
line connections use springlocks and O-rings.

Continued
Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition
By James D. Halderman

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