Halderman J.D., Linder J. Automotive Fuel and Emissions Control Systems

Подождите немного. Документ загружается.

FUEL PUMPS, LINES, AND FILTERS 241

RIGID LINES All fuel lines fastened to the body, frame, or

engine are made from nylon reinforced plastic or 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 manu-

facturer, 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.

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 usually 3/16'' or

3/8'' (8 or 10 millimeters) and the return line ID is normally 1/4''

(6millimeters).

Fuel-injection systems require special-composition re-

inforced hoses specifically made for these higher-pressure

systems. Similarly, vapor vent lines must be made of ma-

terials that resist fuel vapors. Replacement vent hoses are

usually marked with the designation “EVAP” to indicate their

intended use.

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 with clips.

 SEE FIGURE 19–8 .

FUEL RETURN TUBE

FUEL FEED TUBE

EMISSION

CONTROL TUBE

SCREW

CLIP

FUEL RETURN TUBE

SCREW

CLIP

FUEL RETURN TUBE

FUEL FEED TUBE

FIGURE 19–8 Fuel lines are routed along the frame or body

and secured with clips.

TO INTAKE AIR

DISTRIBUTOR

BYPASS

BACKFIRE VALVE

FROM

AIR CLEANER

STATOR FLAP

RETURN SPRING

POTENTIOMETER

PUMP

CONTACT

VOLTA

E SI

NAL

BALANCE CHAMBER

BALANCE FLAP

FIGURE 19–6 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.

ELECTRICAL

NTA

RESET BUTTON

STEEL BALL

MAGNET

TAR

ET PLATE

CONICAL

RAMP

FIGURE 19–7 Ford uses an inertia switch to turn off the

electric fuel pump in an accident.

242 CHAPTER 19

FUEL-INJECTION LINES AND CLAMPS Hoses used

for fuel-injection systems are made of materials with high resis-

tance to oxidation and deterioration. Replacement hoses for

injection systems should always be equivalent to original equip-

ment manufacturer (OEM) hoses.

Screw-type clamps are essential on injected engines and

should have rolled edges to prevent hose damage.

CAUTION: Do not use spring-type clamps on fuel-

injected engines —they cannot withstand the fuel pres-

sures involved.

FUEL-INJECTION FITTINGS AND NYLON LINES

Because of their operating pressures, fuel-injection systems often

use special kinds of fittings to ensure leakproof connections. Some

high-pressure fittings on GM vehicles with port fuel-injection sys-

tems use O-ring seals instead of the traditional flare connections.

When disconnecting such a fitting, inspect the O-ring for damage

and replace it if necessary. Always tighten O-ring fittings to the

specified torque value to prevent damage.

Other manufacturers also use O-ring seals on fuel line con-

nections. In all cases, the O-rings are made of special materi-

als that withstand contact with gasoline and oxygenated fuel

blends. Some manufacturers specify that the O-rings be re-

placed every time the fuel system connection is opened. When

replacing one of these O-rings, a new part specifically designed

for fuel system service must be used.

Ford also uses spring-lock connectors to join male and

female ends of steel tubing.

 SEE FIGURE 19–9 . 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.

General Motors has used nylon fuel lines with quick-

connect fittings at the fuel tank and fuel filter since the early

1990s. Like the GM threaded couplings used with steel lines,

nylon line couplings use internal O-ring seals. Unlocking the

metal connectors requires a special quick-connector separa-

tor tool; plastic connectors can be released without the tool.

 SEE FIGURES 19–10 AND 19–11 .

FUEL LINE LAYOUT Fuel pressures have tended to

become higher to prevent vapor lock, and a major portion of

the fuel routed to the fuel-injection system returns to the tank

by way of a fuel return line or return-type systems. This allows

better control, within limits, of heat absorbed by the gasoline

as it is routed through the engine compartment. Throttle-body

and multiport injection systems have typically used a pressure

regulator to control fuel pressure in the throttle body or fuel rail

and also allow excess fuel not used by the injectors to return

to the tank. However, the warmer fuel in the tank may create

problems, such as an excessive rise in fuel vapor pressures in

the tank.

RELEASE

LIPS

CAGE

SLIDE TOOL

INTO CONNECTOR

SPECIAL

TOOL

FIGURE 19–10 Ford spring-lock connectors require a

special tool for disassembly.

WHITE INDICATOR RING

O-RINGS

LIP

FEMALE FITTING

GARTER SPRING

MALE FITTING

DISASSEMBLED

CAGE

WHITE INDICATOR

RING (LOOSE)

ASSEMBLED

FIGURE 19–9 Some Ford metal line connections use spring

locks and O-rings.

Just How Much Fuel Is Recirculated?

Approximately 80% of the available fuel pump volume

is released to the fuel tank through the fuel pressure

regulator at idle speed. As an example, a passenger

vehicle cruising down the road at 60 miles per hour

gets 30 miles per gallon. With a typical return-style

fuel system pumping about 30 gallons per hour from

the tank, it would therefore burn 2 gallons per hour

and return about 28 gallons per hour to the tank!

FREQUENTLY ASKED QUESTION

FUEL PUMPS, LINES, AND FILTERS 243

POSITIVE DISPLACEMENT PUMP A positive displace-

ment pump is a design that forces everything that enters the

pump to leave the pump.

In the roller cell or vane pump, the impeller draws fuel into

the pump and then pushes it out through the fuel line to the injec-

tion system. All designs of pumps use a variable-sized chamber

to draw in fuel. When the maximum volume has been reached,

the supply port closes, and the discharge opens. Fuel is then

forced out the discharge as this volume decreases. The cham-

bers are formed by rollers or gears in a rotor plate. Because this

type of pump uses no valves to move the fuel, the fuel flows

steadily through the entire pump housing, including the electrical

portion which keeps the pump cool. Usually, only when a vehicle

runs out of fuel is there a risk of pump damage.

Most electric fuel pumps are equipped with a fuel outlet

check valve that closes to maintain fuel pressure when the

pump shuts off. Residual or rest pressure prevents vapor lock

and hot-start problems on these systems.

 FIGURE 19–13 shows the pumping action of a rotary

vane pump . The pump consists of a central impeller disk,

How Can an Electric Pump Work Inside a Gas

Tank and Not Cause a Fire?

Even though fuel fills the entire pump, no burnable

mixture exists inside the pump because there is no

air and no danger of commutator brush arcing, ignit-

ing the fuel.

FREQUENTLY ASKED QUESTION

METAL COLLAR

QUICK-CONNECT FITTING

INSTALLATION

BLOW

PLASTIC COLLAR

QUICK-CONNECT FITTING

REMOVAL

TWIST

FIGURE 19–11 Typical quick- connect

steps.

With late-model vehicles, there has been some concern

about too much heat being sent back to the fuel tank, causing

rising in-tank temperatures and increases in fuel vaporization

and volatile organic compound (VOC) (hydrocarbon) emis-

sions. To combat this problem, manufacturers have placed the

pressure regulator back by the tank instead of under the hood

on mechanical returnless systems. In this way, returned fuel is

not subjected to the heat generated by the engine and the un-

derhood environment. To prevent vapor lock in these systems,

pressures have been raised in the fuel rail, and injectors tend

to have smaller openings to maintain control of the fuel spray

under pressure.

Not only must the fuel be filtered and supplied under ad-

equate pressure, but there must also be a consistent volume

of fuel to assure smooth engine performance even under the

heaviest of loads.

ELECTRIC FUEL PUMPS

The electric fuel pump is a pusher unit. When the pump is

mounted in the tank, the entire fuel supply line to the engine

can be pressurized. Because the fuel, when pressurized, has a

higher boiling point, it is unlikely that vapor will form to interfere

with fuel flow.

Most vehicles use the impeller or turbine pumps.

 SEE

FIGURE 19–12 . All electrical pumps are driven by a small elec-

tric motor, but the turbine pump turns at higher speeds and is

quieter than the others.

244 CHAPTER 19

moves the fuel to create pressure. This design of pump is a

nonpositive displacement pump design.

A turbine pump is the most common because it tends

to be less noisy. Also known as peripheral and side-channel

pumps, these units use an impeller that accelerates the fuel

particles before actually discharging them into a tract where

they generate pressure via pulse exchange. Actual pump vol-

ume is controlled by using a different number of impeller blades,

and in some cases a higher number of impellers, or different

shapes along the side discharge channels. These units are fit-

ted more toward lower operating pressures of less than 60 PSI.

 SEE FIGURE 19–15 for an example of a two-stage turbine

pump. The turbine impeller has a staggered blade design to

minimize pump harmonic noise and to separate vapor from

the liquid fuel. The end cap assembly contains a pressure re-

lief valve and a radio-frequency interference (RFI) suppression

module. The check valve is usually located in the upper fuel pipe

connector assembly.

After fuel passes through the strainer, it is drawn into

the lower housing inlet port by the impellers. It is pressur-

ized and delivered to the convoluted fuel tube for transfer

through a check valve into the fuel feed pipe. A typical elec-

tric fuel pump used on a fuel-injection system delivers about

40 to 50gallons per hour or 0.6 to 0.8 gallon per minute at a

pressure of 70 to 90 PSI.

MODULAR FUEL SENDER ASSEMBLY The modular

fuel sender consists of a fuel level sensor, a turbine pump,

and a jet pump. The reservoir housing is attached to the cover

containing fuel pipes and the electrical connector. Fuel is trans-

ferred from the pump to the fuel pipe through a convoluted (flex-

ible) fuel pipe. The convoluted fuel pipe eliminates the need for

rubber hoses, nylon pipes, and clamps. The reservoir dampens

fuel slosh to maintain a constant fuel level available to the roller

vane pump; it also reduces noise.

Some of the flow, however, is returned to the jet pump for

recirculation. Excess fuel is returned to the reservoir through

one of the three hollow support pipes. The hot fuel quickly

FILTER (SOCK)

FLOAT

ARM

GROUND

FUEL

DELIVERY

PIPE

ELECTRICAL

CONNECTOR

OUTLET

PRESSURE

RELIEF VALVE

OUTLET

CHECK

VALVE

MOTOR

ARMATURE

ROLLER

CELL PUMP

INLET

PUMP

FUEL LEVEL

GAUGE UNIT

PUMP DETAIL

FIGURE 19–12 A roller cell-type electric fuel pump.

INLET

OUTLET

PUMP HOUSING

ROLLER

IMPELLER DISK

FIGURE 19–13 The pumping action of an impeller or rotary

vane pump.

several rollers or vanes that ride in notches in the impeller,

and a pump housing that is offset from the impeller centerline.

The impeller is mounted on the end of the motor armature and

spins whenever the motor is running. The rollers are free to

slide in and out within the notches in the impeller to maintain

sealing contact. Unpressurized fuel enters the pump, fills the

spaces between the rollers, and is trapped between the impel-

ler, the housing, and two rollers. An internal gear pump, called

a gerotor , is another type of positive displacement pump that

is often used in engine oil pumps. It uses the meshing of in-

ternal and external gear teeth to pressurize the fuel.

 SEE

FIGURE 19–14 for an example of a gerotor-type fuel pump

that uses an impeller as the first stage and is used to move the

fuel gerotor section where it is pressurized.

HYDROKINETIC FLOW PUMP DESIGN The word hydro

means liquid, and the term kinetic refers to motion, so the term

hydrokinetic pump means that this design of pump rapidly

FUEL PUMPS, LINES, AND FILTERS 245

mixes with the cooler fuel in the reservoir; this minimizes the

possibility of vapor lock. In these modules, the reservoir is

filled by the jet pump. Some of the fuel from the pump is

sent through the jet pump to lift fuel from the tank into the

reservoir.

ELECTRIC PUMP CONTROL CIRCUITS Fuel pump cir-

cuits are controlled by the fuel pump relay. Fuel pump relays are

activated initially by turning the ignition key to on, which allows

the pump to pressurize the fuel system. As a safety precaution,

the relay deenergizes after a few seconds until the key is moved

to the crank position. Once an ignition coil signal, or “tach” sig-

nal, is received by the engine control computer, indicating the

engine is rotating, the relay remains energized even with the key

released to the run position.

CHRYSLER. On Chrysler vehicles, the PCM must receive an

engine speed (RPM) signal during cranking before it can ener-

gize a circuit driver inside the power module to activate an

automatic shutdown (ASD) relay to power the fuel pump, igni-

tion coil, and injectors. As a safety precaution, if the RPM signal

to the logic module is interrupted, the logic module signals the

power module to deactivate the ASD, turning off the pump, coil,

Why Are Many Fuel Pump Modules

Spring Loaded?

Fuel modules that contain the fuel pickup sock, fuel

pump, and fuel level sensor are often spring loaded

when fitted to a plastic fuel tank. The plastic material

shrinks when cold and expands when hot, so having

the fuel module spring loaded ensures that the fuel

pickup sock will always be the same distance from

the bottom of the tank.

 SEE FIGURE 19–16.

FREQUENTLY ASKED QUESTION

FUEL IN

FUEL OUT

SHELL

INLET SEAL

INLET BODY

INLET PLATE

GEROTOR

ASSEMBLY

IMPELLER

DRIVER

O-RING

ENDCAP

BRUSH CARRIER

ASSEMBLY

ARMATURE

FIELD

HOUSING

OUTLET

PLATE

FIGURE 19–14 An exploded view of a gerotor electric fuel pump.

246 CHAPTER 19

and injectors. In some vehicles, the oil pressure switch circuit

may be used as a safety circuit to activate the pump in the igni-

tion switch run position.

GENERAL MOTORS. General Motors systems energize the

pump with the ignition switch to initially pressurize the fuel

lines but then deactivate the pump if an RPM signal is not

received within one or two seconds. The pump is reactivated

as soon as engine cranking is detected. The oil pressure

sending unit serves as a backup to the fuel pump relay on

some vehicles. In case of pump relay failure, the oil pressure

switch will operate the fuel pump once oil pressure reaches

about 4 PSI (28 kPa).

FORD. Most Ford vehicles with fuel injection have an inertia

switch between the fuel pump relay and fuel pump. When the

ignition switch is turned to the on position, the electronic engine

control (EEC) power relay energizes, providing current to the

fuel pump relay and a timing circuit in the EEC module. If the

RPM signal is not received by the PCM within about one sec-

ond, the timing circuit opens the ground circuit to deenergize

the fuel pump relay and shut down the pump. This circuit is

designed to prepressurize the system. Once the key is turned to

the start position, power to the pump is sent through the relay

and inertia switch.

The inertia switch opens under a specified impact, such as

a collision. When the switch opens, current to the pump shuts off

FUEL IN

FUEL OUT

FIRST PUMP

STAGE

SECOND PUMP

STAGE

CHECK VALVE

ARMATURE

FIGURE 19–15 A cutaway view of a typical two-stage turbine electric fuel pump.

FIGURE 19–16 A typical fuel pump module assembly, which

includes the pickup strainer and fuel pump, as well as the

fuel-pressure sensor and fuel level sensing unit.

FUEL PUMPS, LINES, AND FILTERS 247

because the fuel pump relay will not energize. The switch must

be reset manually by opening the trunk and depressing the reset

button before current flow to the pump can be restored.

 SEE

FIGURE 19–17 for a schematic of a typical fuel system that uses

an inertia switch in the power feed circuit to the electric fuel pump.

PUMP PULSATION DAMPENING Some manufacturers

use an accumulator in the system to reduce pressure pulses

and noise. Others use a pulsator located at the outlet of the

fuel pump to absorb pressure pulsations that are created by

the pump. These pulsators are usually used on roller vane

pumps and are a source of many internal fuel leaks.

 SEE

FIGURE 19–18 .

NOTE: Some experts suggest that the pulsator be removed

and replaced with a standard section of fuel line to prevent

the loss of fuel pressure that results when the connections

on the pulsator loosen and leak fuel back into the tank.

VARIABLE SPEED PUMPS Another way to help reduce

noise, current draw, and pump wear is to reduce the speed of

the pump when less than maximum output is required. Pump

HOT IN START OR RUN

FUSE

BLOCK

10A

640

R/T

R/Y

R/Y H

C105

C222

TACHOMETER

WARNING

INDICATORS

UPSHIFT

INDICATOR

57 BK

S153

GRD

SEE GROUND

AT RIGHT

HOT AT ALL TIMES

FUSE

LINK

18 GA BROWN

37 Y

EEC

POWER

RELAY

57 BK

G101

BATTERY

57 BK

787 PK/BK

ELECTRIC

FUEL

PUMP

787 PK/BK

C300

C256

361 R

FUEL

PUMP

RELAY

361 R

C254

C255

97 T/LG

19 11 12

SOLID STATE

1 2

57 BK

EEC

POWER

RELAY

S153

C1`5

INERTIA

SWITCH

OPENS

IMPACT

57 BK

G107

ELECTRONIC

CONTROL ASSY

DIODE

S151

POWER INPUT

C254

347 BK

347 BK/Y

C126

347 BK/Y

FROM

A/C HEATER

361

FIGURE 19–17 A schematic showing that an inertia switch is connected in series between the fuel pump relay and the

fuel pump.

1/4" GAP

FUEL FROM

OUTLET OF PUMP

FUEL OUT

DIAPHRAGM

PULSATOR

FUEL

PUMP

FUEL INLET

STRAINER/FILTER

FIGURE 19–18 A typical fuel pulsator used mostly with roller

vane-type pumps to help even out the pulsation in pressure

that can cause noise.

248 CHAPTER 19

speed and pressure can be regulated by controlling the voltage

supplied to the pump with a resistor switched into the circuit or

by letting the engine-control computer pulse-width modulate

(PWM) the voltage supply to the pump, through a separate fuel

pump driver electronic module. With slower pump speed and

pressure, less noise is produced.

FILTER

INLET

FLOW

CLAMP

SSG TYPE O-RING FITTING

(BOTH ENDS)

OUTLET

FRONT

SCREW

O-RING TYPE

BRACKET

CLAMP TYPE

IDENTIFICATION

LABEL

FIGURE 19–19 Inline fuel filters are usually attached to the

fuel line with screw clamps or threaded connections. The fuel

filter must be installed in the proper direction or a restricted

fuel flow can result.

FUEL FILTERS

Despite the care generally taken in refining, storing, and de-

livering gasoline, some impurities get into the automotive fuel

system. Fuel filters remove dirt, rust, water, and other contami-

nation from the gasoline before it can reach the fuel injectors.

Most fuel filters are designed to filter particles that are 10 to

20microns or larger in size.

The useful life of many filters is limited, but vehicles that

use a returnless-type fuel-injection system often use filters that

are part of the fuel pump assembly and do have any specified

replacement interval. This means that they should last the life

of the vehicle. If fuel filters are not replaced according to the

manufacturer’s recommendations, they can become clogged

and restrict fuel flow.

In addition to using several different types of fuel filters, a

single fuel system may contain two or more filters. The inline

filter is located in the line between the fuel pump and the throttle

body or fuel rail.

 SEE FIGURE 19–19 . This filter protects the

system from contamination but does not protect the fuel pump.

The inline filter usually is a metal or plastic container with a

pleated paper element sealed inside.

Fuel filters may be mounted on a bracket on the fender

panel, a shock tower, or another convenient place in the

engine compartment. They may also be installed under the

vehicle near the fuel tank. Fuel filters should be replaced

according to the vehicle manufacturer’s recommenda-

tions, which range from every 30,000 miles (48,000 km) to

TECH TIP

Be Sure That the Fuel Filter Is Installed Correctly

The fuel filter has flow direction, and if it is installed

backwards, the vehicle will most likely have a re-

stricted exhaust (low power at higher engine speeds

and loads).

All injectors, throttle body or port, are fitted with

one or more filter screens or strainers to remove any

particles (generally 10 microns, or 0.00039 in.) that

might have passed through the other filters. These

screens, which surround the fuel inlet, are on the

side of throttle-body injectors and are inserted in the

top of port injectors.

 SEE FIGURE 19–20.

FUEL PUMP TESTING

Fuel pump testing includes many different tests and proce-

dures. Even though a fuel pump can pass one test, it does

not mean that there is not a fuel pump problem. For example,

if the pump motor is rotating slower than normal, it may be

able to produce the specified pressure but not enough vol-

ume to meet the needs of the engine while operating under

a heavy load.

TESTING FUEL PUMP PRESSURE Fuel pump–regulated

pressure has become more important than ever with a more exact

fuel control. Although an increase in fuel pressure does increase

fuel volume to the engine, this is not the preferred method to

add additional fuel as some units will not open correctly at the

increased fuel pressure. On the other side of the discussion,

many newer engines will not start when fuel pressure is just a few

100,000 miles (160,000 km) or longer. Fuel filters that are

part of the fuel pump module assemblies usually do not

have any specified service interval.

FUEL PUMPS, LINES, AND FILTERS 249

PSIlow. Correct fuel pressure is very important for proper engine

operation. Most fuel-injection systems operate at either a low

pressure of about 10 PSI or a high pressure of between 35and

45 PSI.

FINAL FILTER

(FILTER BASKET)

UPPER

O-RING

PORT

FUEL

INJECTOR

LOWER

O-RING

PINTLE CAP

(DISCHARGE END CAP)

FIGURE 19–20 The final filter, also called a filter basket , is

the last filter in the fuel system.

(a)

Normal Operating

Pressure

(PSI)

Maximum Pump

Pressure (PSI)

Low-pressure TBI units 9–13 18–20

High-pressure TBI units 25–35 50–70

Port fuel-injection

systems

35–45 70–90

Central port fuel

injection (GM)

55–64 90–110

(b)

TECH TIP

The Ear Test

No, this is not a test of your hearing but rather us-

ing your ear to check that the electric fuel pump is

operating. The electric fuel pump inside the fuel tank

is often difficult to hear running, especially in a noisy

shop environment. A commonly used trick to bet-

ter hear the pump is to use a funnel in the fuel filter

neck.

 SEE FIGURE 19–21.

FIGURE 19–21 (a) A funnel helps in hearing if the electric fuel

pump inside the gas tank is working. (b) If the pump is not run-

ning, check the wiring and current flow before going through

the process of dropping the fuel tank to remove the pump.

In both types of systems, maximum fuel pump pressure

is about double the normal operating pressure to ensure that a

continuous flow of cool fuel is being supplied to the injector(s)

to help prevent vapor from forming in the fuel system. Although

250 CHAPTER 19

vapor or foaming in a fuel system can greatly affect engine

operation, the cooling and lubricating flow of the fuel must be

maintained to ensure the durability of injector nozzles.

To measure fuel pump pressure, locate the Schrader valve

and attach a fuel-pressure gauge.

 SEE FIGURE 19–22 .

NOTE: Some vehicles, such as those with General

Motors TBI fuel-injection systems, require a specific

fuel-pressure gauge that connects to the fuel system.

Always follow the manufacturer’s recommendations and

procedures.

REST PRESSURE TEST If the fuel pressure is accept-

able, then check the system for leakdown. Observe the pres-

sure gauge after five minutes.

 SEE FIGURE 19–23 . The

pressure should be the same as the initial reading. If not, then

the pressure regulator, fuel pump check valve, or the injectors

are leaking.

DYNAMIC PRESSURE TEST To test the pressure dynam-

ically, start the engine. If the pressure is vacuum referenced,

then the pressure should change when the throttle is cycled. If

it does not, then check the vacuum supply circuit. Remove the

vacuum line from the regulator and inspect for any presence

of fuel.

 SEE FIGURE 19–24 . There should never be any fuel

present on the vacuum side of the regulator diaphragm. When

the engine speed is increased, the pressure reading should

remain within the specifications.

Some engines do not use a vacuum-referenced regulator.

The running pressure remains constant, which is typical for a

mechanical returnless-type fuel system. On these systems, the

pressure is higher than on return-type systems to help reduce

the formation of fuel vapors in the system.

TECH TIP

The Rubber Mallet Trick

Often a no-start condition is due to an inoperative

electric fuel pump. A common trick is to tap on the

bottom of the fuel tank with a rubber mallet in an at-

tempt to jar the pump motor enough to work. Instead

of pushing a vehicle into the shop, simply tap on the

fuel tank and attempt to start the engine. This is not

a repair but rather a confirmation that the fuel pump

does indeed require replacement.

FIGURE 19–22 The Schrader valve on this General Motors

3800 V-6 is located next to the fuel-pressure regulator.

Bar

REST PRESSURE

FUEL GAUGE

REGULATOR

NO FUEL

RETURNED

TO TANK

CHECK VALVE

IN F

EL P

FIGURE 19–23 The fuel system should hold pressure if the

system is leak free.

TECH TIP

The Fuel-Pressure Stethoscope Test

When the fuel pump is energized and the engine is not

running, fuel should be heard flowing back to the fuel

tank at the outlet of the fuel pressure regulator.

 SEE

FIGURE 19–25. If fuel is heard flowing through the

return line, the fuel pump pressure is higher than the

regulator pressure. If no sound of fuel is heard, either

the fuel pump or the fuel-pressure regulator is at fault.