36559209 fuel system for gasoline engines 1

8/13/2019 36559209 Fuel System for Gasoline Engines 1

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Chapter 1

THE FUEL SYSTEM FOR

GASOLINE ENGINES

A fuel system provides a combustible air-fuel mixture to power the engine.

Todays gasoline cars commonly use carburetors and injection systems to control

amount of fuel that mixes with air.

THE MAIN COMPONENTS

Pictured in Fig.-! the main components of the fuel system for gasoline engines

are"

F#$% TA&'.

F#$% P#(P.

F#$% F)%T$*.

F#$% %)&$+.

A)* F)%T$*.

F#$%-($T$*)&, $)/$.

Fig. 1-1.Basic parts of the fuel system for gasoline engines.

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FUEL TANK

An automotive fuel tan0 must be safely held. )t is normally mounted in the rear of

the car! under the trun0 or rear seat. +ee Fig. -1. The function of fuel tan0 is to

store the gasoline and supply fuel during engine operation. Fuel tan0s are usually

made of thin sheet of metal or plastic. An average fuel tan0 capacity is around 1

to 12 gallons 342 to 52 liters6. Fuel tan0 caps are sealed to prevent the escape of

fuel and fuel vapors from the tan0s. This cap has pressure and vacuum valves

that only open under abnormal conditions of high pressure or high vacuum. +ee

Fig. -7.

Fig. 1-2.Basic parts of fuel tank.

Fig. 1-3.Fuel tank cap.

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The gasoline tan0 contains a float! which is attached to resistance device. +ee

Fig. -4. The travel of the float up and down causes the resistance to vary. %ow

fuel level causes float to move down8 as a result! tan0 unit has high resistance.

%ow current flow does not heat bi-metal strip and therefore! gauge shows low.

9hen the tan0 is full! this ma0es the float to move up. :n the other hand! the

resistor moves in low resistance position. ;igh current flows through gauge and

tan0 unit heats bi-metal strip. +trip bends and moves needle to full.

Fig. 1-4. Fuel gauge operation.

FUEL PUMP

A fuel pump draws fuel from the tan0 and forces it to the fuels metering device.

There are two basic types of fuel pumps! mechanical and electrical pumps.

Mechanical fuel pump

An eccentric lobe of the engine camshaft usually powers a mechanical fuel

pump. (echanical fuel pump is commonly used with carburetor type fuel system.

The mechanical fuel pump consists of a roc0er arm! return spring! diaphragm!

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Fig. 1-. Basic parts and operations of mechanical fuel pump.

diaphragm spring! and chec0 valves. +ee Fig. -2. 9hen the eccentric lobe is

pushed on the roc0er arm! this pulls the diaphragm down and compresses the

diaphragm spring. +ince the area in the pumping chamber increases! a vacuum

pulls fuel through the inlet chec0 valve. This fills the pump with fuel. 9hen the

eccentric lobe rotates away from the pump roc0er arm! this releases the

diaphragm. The diaphragm spring then pushes on the diaphragm and

pressuri


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Electric fuel pump

An electric fuel pump! li0e a mechanical fuel pump! produces fuel pressure and

flow for the fuel-metering device of a fuel system. $lectric fuel pumps are

commonly used in gasoline fuel injection systems. An electric fuel pump can be

located inside the fuel tan0 or between the tan0 and the engine. There are three

common types of electric fuel pumps! an impeller! a roller vane! and sliding vane.

+ee Fig. -=.

Fig. 1-!. Electric fuel pumps types and operations.

Impeller electric fuel pump

This is a centrifugal type pump. &ormally! it is located inside the fuel tan0. This

pump uses a small ./. motor to spin the impeller. The impeller blades cause

the fuel to fly outward due to centrifugal force. This produces enough pressure to

move the fuel through the fuel lines.

Roller ane electric fuel pump

This is a positive displacement pump 3each pump rotation moves a specific

amount of fuel6.

9hen the rotor disc and rollers spin! they pull fuel in one side. Then the fuel is

trapped and pushed to a smaller area on the opposite side of the pump housing.

This s>uee


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Sli!in" ane electric fuel pump

A sliding vane electric fuel pump is similar to a roller vane pump. anes 3blades6

are used instead of rollers.

FUEL FILTER

:ne or more filters are fitted in the fuel system to stop contaminants 3rust! water!

corrosion! dirt6 from entering the carburetor or injection systems. +ome fuel filters

use pleated paper elements to trap dirt in the fuel. :thers use a sintered bron


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The function of an air filter is to remove dirt and dust from the air entering the

engine inta0e manifold. (ost air filters are made of paper element. +ee Fig. -.

Fig. 1-#. Air filter.

FUEL # METERIN$ %E&ICE

A fuel-metering device which controls the amount of fuel that mixes with air.

The fuel-metering device for gasoline engines is divided into two systems"

/A*?#*$T:* +B+T$(.

F#$% )&C$/T):& +B+T$(.

CAR'URETOR S(STEM


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A carburetor is basically a device for mixing air and fuel in the correct proportions

for efficient combustion. The carburetor bolts to the engine inta0e manifold. The

air cleaner fits over the top of the carburetor to trap dust and dirt. +ee Fig. -5.

Functions of the carburetor are"

To mix air with gasoline in suitable proportions to obtain the desired

performance of the engine.

To atomiuid fuel.

Fig. 1-$. !ar"uretor "olts to engine intake manifold.

'ASIC CAR'URETOR S(STEMS

/arburetor systems are a networ0 of passages and related parts that help control

the air-fuel ratio under a specific engine operating condition. Also called a

carburetor circuits! each system applies a predetermined air-fuel mixture as the

temperature! speed! and load of the engine change.

An automotive carburetor! using its various systems! must be capable of

providing air-fuel ratios of approximately"

#


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" for cold engine starting.

= " for idling.

2 " for part throttle.

7 " for full acceleration. " for normal cruising at highway speeds.

The seven basic carburetor systems are"

F%:AT +B+T$( 3maintains supply of fuel in carburetor bowl6.

)%$ +B+T$( 3provides a small amount of fuel for low speed engine

operation6.

:FF-)%$ +B+T$( 3provides correct air-fuel mixture slightly above idle

speeds6.

A//$%$*AT):& +B+T$( 3s>uirts fuel into air horn when throttle valve

opens and engines speed increases6.

;),;-+P$$ +B+T$( 3supplies lean air-fuel mixture at cruising speeds6.

F#%%-P:9$* +B+T$( 3enriches fuel mixture slightly when engine

power demands are high6.

/;:'$ +B+T$( 3provides extremely rich air-fuel mixture for cold engine

starting6.

FLOAT S(STEM

Function) To maintain the correct level of fuel in carburetor bowl! and to supply

fuel for all circuits.

Part*)Fuel bowl! float! needle valve! needle seat! and bowl vent. +ee Fig. -D.

Operation)9hen the engine speed or load increases! fuel is rapidly pulled out of

the fuel bowl and into the venturi. This ma0es the fuel level and float drop in thebowl. The needle valve also drops away from its seat. The fuel pump can then

force more fuel into the bowl. As the fuel level in the bowl rises! the float pushes

the needle valve bac0 into the seat. 9hen the fuel level is high enough! the float

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closes the opening between the needle valve and seat. 9ith the engine running!

the needle valve usually lets some fuel lea0 into the bowl.

Fig. 1-1%. Basic parts and operations of the float system.

I%LE S(STEM

Function)To provide a small amount of fuel for low speed engine operation.

3At speeds below approximately DD r.p.m. or 1D (.P.;. 371 0mEhr66.

Part*)(ain discharge tube! a low speed jet! idle air bleed! idle passage! idle

port! bypass! economi


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Fig. 1-11. Basic parts and operations of idle system.

OFF#I%LE S(STEM

Function)To feed more fuel when the throttle plates are partially open.

3Above approximately DD r.p.m. or 1D (.P.;. 371 0mEhr66.

Part*)(ain discharge tube! a low speed jet! idle air bleed! idle passage! idleport! bypass! economi


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Fig. 1-12. Basic parts and operations of the off&idle system.

Operation)The off-idle system begins to function when the driver presses lightly

on the gas pedal. As the throttle plates open! they expose the off-idle ports to

inta0e manifold vacuum. acuum then begins to pull fuel out of the idle screw

port and off-idle ports. This provides enough extra fuel to mix with the additionalair flowing around the throttle plates.

ACCELERATION S(STEM

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Function)To provide extra fuel when changing from the idle circuits to the high-

speed circuits. The acceleration system s>uirts a stream of extra fuel into air horn

whenever the gas pedal is pressed.

Part*)Pump lin0age! acceleration pump! pump chec0 ball! pump reservoir! pump

chec0 weight! and pump no


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Function)To supply the engine air-fuel mixture at normal cruising speeds.

This circuit begins to function when the throttle plates are open wide enough for

venturi.

)t functions from about 1D to 22 (.P.;. 371 to 5 0mEhr6 or 1DDD to 7DDD r.p.m.

Part*)(ain jet! main discharge passage! air bleed! and venturi. +ee Fig. -4.

Operation)9hen engine speed is high enough! airflow through the carburetor

forms a high vacuum in the venturi. The vacuum pulls fuel through the main jet.

Fuel flows through the main jet! which meters the amount of gasoline entering

the circuit. Then! the fuel flows into the main discharge passage! and finally

pulled out the main no


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Fig. 1-1. Basic parts and operations of the full po'er system.

Operation)9hen gas pedal is pushed down for full power! throttle lin0age acts

on metering rod lin0age. (etering rod is lifted out of main jet to add more fuel to

the mixture. 9hen gas pedal is released! the metering rod will move down inside

the main jet! flow is restricted and leaner fuel mixture results.

$ither mechanical lin0age or engine vacuum can be used to operate a metering

rod.

CHOKE S(STEM

Function)To supply an extremely rich air-fuel ratio to aid cold engine starting.

For fuel mixture to burn properly! the fuel entering the inta0e manifold must

atomi


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Part*)/ho0e plates valve! thermostatic spring! and other parts depending upon

cho0e design. +ee Fig. -=.

Fig. 1-1!. Basic parts and operations of the choke system.

Operation)9hen engine is cold! thermostatic spring closes cho0e plates. ;igh

vacuum below cho0e pulls large a mount of fuel out main discharge. 9hen

engine warms! hot air causes thermostatic spring to open cho0e plates.

T(PES OF THE CAR'URETORS

Automotive carburetors are available in single barrel! two-barrel 3two air horns in

single body6! and four-barrel 3four air horns in one body6 designs. All are

illustrated in Fig. -@.

(ultiple barrel carburetors are used to provide increased Gengine breathingH 3air

inta0e6. The amount of fuel and air that enters the engine is a factor limiting

engine horsepower output. $xtra carburetor barrels allow more air and fuel into

the engine at wide-open throttle. This allows the engine to develop more power.

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Fig. 1-1". (ypes of the car"uretors.

Car,uretor primar- an! *econ!ar- circuit*

Two-barrel and four-barrel carburetors are divided into two sections" the primary

and the secondary circuits.

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Theprimary circuitof a carburetor includes the components that operate under

normal driving conditions. +ee Fig. -.

The secondary circuit of a carburetor consists of the components that function

under high engine power output conditions. +ee Fig. -.

A secondary diaphragmis normally used to open the secondary throttle plates!

causing the secondary circuits to function. +ee Fig. -. A diaphragm is

connected to the secondary throttle lever. A vacuum passage runs from this

diaphragm to the venturi in the primary throttle bore.

#nder normal driving conditions! vacuum in the primary is not high enough to

actuate the secondary diaphragm and throttles. The engine would run using only

the primary of the carburetor.

)f the driver presses on the gasoline pedal! the airflow will increase in the primary

circuit producing enough vacuums to operate the secondary diaphragm. acuum

pulls on the diaphragm and compresses the diaphragm spring. This opens the

secondary throttle plates for increased engine horsepower.

Fig. 1-1#. !ar"uretor primary and secondary circuits.

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CAR'URETOR PRO'LEMS

Poor Engine Performance

Air lea0 at carburetor or inta0e manifold.

Air lea0 in fuel line.

/logged or dirty carburetor air filter.

/logged fuel lines or fuel filter.

efective fuel pump.

)ncorrect fuel level in fuel bowl.

irt in carburetor jets and passages.

9orn or inoperative accelerating pump.

efective gas0ets in carburetor.

/logged exhaust system.

%ea0ing vacuum lines.

Poor Idling

)ncorrect adjustment of idle mixture screw.

)ncorrect float level.

+tic0ing float needle valve.

efective gas0et between carburetor and inta0e manifold.


%oose carburetor- to I inta0e manifold nuts.

%oose inta0e manifold attaching bolts.

)dle discharge holes partly clogged.

%ea0ing vacuum lines to accessory e>uipment.

/logged air cleaner.

;igh float levelHard Starting

)ncorrect cho0e adjustment.

efective cho0e.

)ncorrect float level.

efective fuel pump.

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Poor Acceleration

Accelerator pumps inoperative.

Accelerator pump leather hard or worn.

/logged accelerator jets or passages.

efective ball chec0s in accelerator system.

)ncorrect fuel level.

Carburetor Floods

Float level too high.

+tic0 float needle valve.


/rac0ed carburetor body.

Excessive Fuel Consumption


Fuel lea0s in carburetor or lines.

irty air cleaner.

;igh float level.

irty carburetor.

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$ASOLINE IN.ECTION S(STEM

A gasoline injection system has several possible advantages over a carburetor

type fuel system. A few of these include"

)mproved atomiual flow of fuel into each cylinder6.

+moother idle 3lean fuel mixture can be used without rough idle because

of better fuel distribution6.

)mproved fuel economy 3high efficiency because of more precise fuel

metering! atomi


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Fig. 1-1$-A. )ingle&point fuel in*ection. &. +ulti&point fuel in*ection.

MULTI#POINT FUEL IN.ECTION S(STEM

There are two common types of multi-point fuel injection systems) ;B*A#%)/-

($/;A&)/A% F#$% )&C$/T):& +B+T$( and $%$/T*:&)/ F#$%

)&C$/T):&+B+T$(.

MULTI#POINT H(%RAULIC# MECHANICAL FUEL IN.ECTION

S(STEM

;ydraulic-mechanical fuel injection system is a continuous injection system that

sprays fuel into the inta0e manifold all of the time. Anytime the engine is running!

some fuel is forced out of the injector no


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Fig. 1-2%. ,ydraulic&mechanical fuel in*ection type -&etronic.

Operation

:n starting the engine! the electric fuel pump draws gasoline out of the tan0 and

passes it to the accumulator. +ee Fig. -1D. After passing accumulator! thepressuriuantity of the fuel delivered to the

injectors. At idle! low airflow only moves sensor plate a little. %ever arm pushes

up lightly on the fuel control plunger and opens a slit to allow fuel to the chamber.

Although fuel pressure now acts on both sides of the diaphragm! the force of the

spring moves the diaphragm downwards and opens the valve at the center of the

diaphragm to release the fuel to the injector. The flow of fuel from the chamber

slightly lowers the downward force on the diaphragm! so a valve-open position is

reached! which corresponds to the amount that the control plunger is moved.

:pening the throttle plate will give a greater air flow! so the disc will raise further!

which! in turn! will raise the control plunger and allow more fuel to pass to the

chamber. These extra fuel flows will more than ma0e up for the fuel that is

escaping past the valve to the injector! so the extra downward force produced by

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the fuel pressure lowers the diaphragm! opens the valve further and increases

the >uantity of fuel going to the injector.

Fuel !i*tri,utor an! airflo0 *en*or

This controls the >uantity of fuel delivered to the injectors. The air sensor! see

Fig.-1! consists of a venturi 36 in the induction pipe into which is fitted a

movable disc 316. Attached to the disc is a counter-balanced lever 376! which acts

on a control plunger 346. (ounted around the plunger are a number of diaphragm

valves 326! one for each injector. The purpose of these valves is to provide a fuel

supply to the injectors that are proportional to the movement of the control

plunger.

Fig. 1-21. -&etronic fuel distri"utor and airflo' sensor.

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Continuou* fuel in1ector

A continuous fuel injector is simply a spring-loaded valve. +ee Fig. -11. )t injects

fuel all the time when the engine is running. A spring holds the valve in a

normally closed position. A filter in the injector traps dirt. The injector is usually

push-fitted into rubber bushings in the cylinder head or inta0e manifold. 9ith the

engine off! the injector spring holds the injector valve closed. This prevents fuel

from dripping into the engine. 9hen the engine is running! fuel pressure builds

from fuel distributor pushes the injector valve open. A steady stream of gasoline

then sprays toward each engine inta0e valve. The fuel is pulled into the engine

when the inta0e valves open.

Fig. 1-22. !ontinuous in*ector.

Fuel accumulator

The fuel accumulator is spring-loaded diaphragm used in an injection system to

dampen pressure pulses of the pump. +ee Fig. -17. The accumulator may also

maintain pressure when the engine is shut down. This aids faster engine

restarting.

Fig. 1-23. Fuel accumulator.

+arm#up re"ulator

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This controls the mixture enrichment during engine warm-up. )t consists of a

valve! operated by a bimetallic strip. +ee Fig. -14. 9hen the engine is cold!

open valve reduce pressure acting on the end of plunger. This tends to increase

fuel mixture. uring warm-up! electrical current heats bi-metal strip and gradually

closes valve.

Fig. 1-24. /arm&up regulator.

Thermo 2 time *0itch

Thermo I time switch energi


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A cold-start injector is an additional fuel injector valve used to supply extra

gasoline for cold engine starting. +ee Fig. -1=. Thermo-time switch is used to

operate cold-start injector.

Fig. 1-2!. !old&start in*ector.

I!le air ,-pa** ale

The idle air bypass valve is operated by a bimetallic spring or expansion

element. The function of this valve is to supply more air to engine during the

warm-up. The additional airflow causes a greater deflection of the airflow meter

plate. This causes the engine to idle at a higher speed during warm-up! as a

result of which it runs smoothly. 9hen the engine warms up! this valve closes off.

The idle air bypass valve is designed somewhat li0e a sliding gate valve in that it

should be fully open on a cold engine and closed on a warm engine.

+ee Fig.-1@.

Fig. 1-2". dle air "ypass ale.

Fuel pre**ure re"ulator

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The function of fuel pressure regulator is to maintain constant fuel pressure

entering fuel distributor. The fuel pressure regulator consists of a fuel valve! and

spring. +ee Fig. -1. 9hen fuel pressure is low 3initial engine starting6! the

spring holds the fuel valve closed. This causes pressure to build as fuel flows into

the regulator from the electric fuel pump. 9hen a preset pressure is reached!

pressure acts on the valve. The valve compresses the spring and opens the fuel

valve. Fuel can flow bac0 to the fuel tan0. This limits the maximum fuel pressure

entering the fuel distributor.

Fig. 1-2#. Fuel pressure regulator.

I!le mi3ture a!1u*tment *cre0 4CO a!1u*tment5

To adjust idle mixture of the engine.

KE#.ETRONIC S(STEM

/loser matching of the mixture to meet changing loads and operating conditions

and the introduction of stricter emission control regulations have induced the

manufacturers to modify the '-Cetronic system. The modified system is called

'$-Cetronic.

/ontrol of the mechanical system by electronic means allows the mixture to beset more accurately! and by virtue of the inherent GintelligenceH of the electronic

control unit 3$/#6! the modified system is able to vary the mixture to suit a wide

range of operating conditions.

/omparing the '$ system shown in Fig. -15 with the ' system! the following

parts are some of the differences"

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Fuel pressure regulator-more precise control of the system fuel pressure

is obtained by using a modified regulator valve! which ta0es into account

manifold depression. %ow engine vacuum would indicate high engine load.

+pring could then hold regulator closed to increase fuel pressure for more

power. ;igh engine vacuum would indicate low load. acuum would act on

diaphragm! opening regulator return to tan0. This would reduce or limit fuel

pressure.

Electro-hydraulic pressure actuator-Functions as a fine mixture

adjustment control to vary the airEfuel ratio slightly to suit all engine conditions!

especially warm-up! acceleration and full-load operation.

Fig. 1-2$. ,ydraulic&mechanical fuel in*ection type -E&etronic.

Electronic control unit computer!- Acts as the brain of the system. )t

analyses the signals it receives from the throttle valve switch! airflow

potentiometer! lambda sensor! and temperature sensors! and then sends

output signals to the actuators! which control the fuel mixture.

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H(%RAULIC#MECHANICAL FUEL IN.ECTION S(STEM PRO'LEMS


/logged or dirty air filter.


efective fuel pump.

irty injectors.

efective injectors.


efective fuel distributor.

efective airflow sensor.

efective computer in '$-jetronic system.

efective sensors in '$- jetronic system.

efective electro-hydraulic pressure actuator in '$-jetronic system.

Air lea0 at inta0e manifold.


efective fuel pressure regulator.

Hard Starting

efective thermo-time switch.

efective cold-start injector.

efective warm-up regulator in '-jetronic system.

efective idle air bypass valve.

efective fuel pump.


efective fuel accumulator.

irty injectors.

efective injectors.

Air in the fuel line.



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efective engine coolant temperature sensor in '$-jetronic system.






efective warm-up regulator in '-jetronic system.


efective lambda sensor in '$-jetronic system.



efective injectors.

irty injectors.

Fuel lea0ing.

efective engine coolant temperature sensor in '$-jetronic system.

MULTI#POINT ELECTRONIC FUEL IN.ECTION S(STEM(ulti-point electronic fuel injection system is indirect injection. This means that

the fuel is sprayed into the engine inta0e manifold ports.)n multi-point electronic fuel injection system uses engine sensors and a

computer to control the opening and closing of injection valve. There are

generally as many injectors as there are cylinders. (ost multi-point electronic

fuel injection systems are intermittent. This means that the injectors are not

energiuence that is

related to valve timing.

There are four common types of multi-point electronic fuel injection systems"

L# .etronic! L6# .etronic! LH # .etronic! and Motronic systems.

,enerally! multi-point electronic fuel injection system can be divided into four

subsystems"

Fuel delivery system.

Air induction system.

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+ensor system.

/omputer control system.

These four subsystems are illustrated in Fig. -7D.

Fuel !elier- *-*temThe fuel delivery system of multi-point $F) system includes an electric fuel pump!

fuel filter! fuel pressure regulator! injector valves! and connecting lines and

hoses. +ee Fig. -7.

Theelectric fuel pumpdraws gasoline out of the tan0 and forces it into the fuel

pressure regulator.

The fuel pressure regulator controls the amount of pressure entering the

injector valves. +ee Fig. -71. 9hen engine vacuum is low! this would indicate

Fig. 1-3%. +ulti&point electronic fuel in*ection.

32

)dle air bypass valve

/onnected to inta0emanifold vacuum

4. computer controlsystem

1. Air induction system

. Fuel deliverysystem

Fuel

!rankshaft

positionsensor

3. )ensor system

istri"utor +

sensor


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Fig. 1-31. Fuel deliery system.

high engine load. +pring could then hold regulator return closed to increase fuelpressure for more power. 9hen engine vacuum is high! this would indicate low

load. acuum would act on diaphragm! opening regulator return to tan0 and

reduce fuel pressure. This maintains a preset amount of fuel pressure for injector

valve operation.

Fig. 1-32. Fuel pressure regulator operation.

A fuel in"ectorfor multi-point $F) system is simply a coil or solenoid operated

fuel valve that sprays and atomi


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Fig. 1-33. +ulti&point EF in*ector operation.

engine. 9hen current flows from the computer through the injector coil! the

magnetic field attracts the injector armature. The injector valve opens. Fuel then

s>uirts into inta0e manifold under pressure.

Air in!uction *-*tem

An air induction system for multi-point $F) typically consists of an air filter! throttle

valves! idle air bypass valve! and connecting ducts.

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$ngine sensors are an electrical device that changes circuit resistance or voltage

with a change in a condition 3temperature! pressure! position of parts! etc.6.

Computer control *-*tem

The computer control system uses electrical data from the sensors to control the

operation of the fuel injectors. A wiring harness connects the engine sensors to

the input of the computer. Another wiring harness connects the output of the

computer to the fuel injectors.

The computer! also called an $%$/T*:&)/ /:&T*:% #&)T 3$/#6! is the

Jbrain of the electronic fuel injection system. The $/# uses sensor output to

calculate when and how long to open the fuel injectors.

To open an injector! the computer connects the injector coil to battery voltage. Toclose the injector! the computer opens the circuit between the battery and the

injector coil.

EN$INE SENSORS

Typical sensors for multi-point $F) system include"

An exhaust gas or oxygen sensor 3%ambda sensor6.

An inta0e manifold pressure sensor.

A throttle position sensor.

An engine coolant temperature sensor.

An airflow sensor.

An inlet air temperature sensor.

A cran0shaft position sensor.

A distributor rpm sensor.

E3hau*t "a* or o3-"en *en*or 4Lam,!a *en*or5

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(easures the oxygen content in the engines exhaust system as a means of

chec0ing combustion efficiency. )t fits into the exhaust manifold or pipe at a point

before the catalytic converter. +ee Fig. -72.

The oxygen sensor voltage output changes with any change in the content of the

exhaust. An increase in oxygen 3lean mixture6 might ma0e the sensor output

voltage decrease. A decrease in oxygen 3rich mixture6 might cause the sensor

output to increase.

)n this way! the sensor supplies data 3different current levels6 to the computer.

The computer can then alter the opening and closing of the injectors to maintain

a correct air-fuel ratio for maximum efficiency.

Fig. 1-3. Ehaust gas or oygen sensor.

Inta8e manifol! pre**ure *en*or(easures the pressure 3vacuum6 inside the engine inta0e manifold. $ngine

manifold pressure is an excellent indicator of engine load. +ee Fig. -7=.

;igh pressure 3low inta0e vacuum6 indicates a high load! re>uiring a rich mixture.

Fig. 1-3!. ntake manifold pressure sensor.

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%ow manifold pressure 3high inta0e vacuum6 indicates very little load! re>uiring a

leaner mixture. The manifold pressure sensor changes resistance with changes

in engine load. This data is used by computer to alter the fuel mixture.

Throttle po*ition *en*or

)s a variable resistor connected to the throttle plate shaft. 9hen the throttle

swings open for more power or closes for less power! the sensor changes

resistance and signals the computer. The computer can then enrich or ma0e lean

mixture as needed. +ee Fig. -7@.

Fig. 1-3". (hrottle position sensor.

En"ine coolant temperature *en*or

(onitors the operating temperature of the engine. )t is mounted so that it is

exposed to the engine coolant. 9hen the engine is cold! the sensor might

provide a high current flow 3low resistance6. The computer would then enrich the

air-fuel mixture for cold engine operation. 9hen the engine warms! the sensor

would supply information 3high resistance6 so that the computer could ma0e the

mixture leaner. +ee Fig. -7.

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Fig. 1-3#. Engine coolant temperature sensor.

Airflo0 *en*or

)s used in many $F) systems to measure the amount of outside air entering the

engine. This helps the computer to determine how much fuel is needed.

The airflow sensor is usually an air flap that operates a variable resistor or hot-

wire air-mass meter.

An airflow sensor! air flap types! is a flap-operated variable resistor. +ee

Fig.-75. Airflow through the sensor causes an air flap to swing to one side.

+ince the air flap is connected to a variable resistor! the amount of airflow into

the engine is converted into an electrical signal for the computer. The computer

can then enrich or ma0e lean mixture as needed.

Fig. 1-3$. Airflo' sensor0 air flap types.

3$


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An airflow sensor! hot-wire air-mass meter types! has a hot wire made of

platinum element which is heated by an electric current sufficient to maintain it at

a constant temperature. +ee Fig. -4D. 9hen the airflow is increased! the cooling

action is greater! so a large current has to be passed through the wire to prevent

a drop in its temperature. The voltage re>uired to provide this current gives an

indication of the inducted air mass. This voltage is signaled to $/# to enable the

$/# to compute initially the basic >uantity of fuel. The >uantity is then slightly

altered to ta0e account of the signals it receives from other engine sensors.

Fig. 1-4%. Airflo' sensor0 hot&'ire air&mass meter types.

Inlet air temperature *en*or

(easures the temperature of the air entering the engine. +ee Fig. -4.

/old air is more dense than warm air! re>uiring a little more fuel. 9arm air is not

as dense as cold air! re>uiring a little less fuel. The air temperature sensor helps

the computer compensate for changes in outside air temperature and maintain

an almost perfect air-fuel mixture ratio.

4%


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Fig. 1-41. An inlet air temperature sensor.

Cran8*haft po*ition *en*or or %i*tri,utor rpm *en*or

/ran0shaft position sensor or distributor rpm sensor is used to detect engine

speed. They allow the computer to change injector opening with changes in

engine rpm. ;igher engine speeds generally re>uire more fuel. %ower engine

speeds re>uire less fuel. This data is used by the computer to alter the fuel

mixture. +ome engines used a cran0shaft position sensor to detect engine

speed. +ee Fig. -41. Another engines used a distributor rpm sensor to detect

engine speed. +ee Fig. -47.

Fig. 1-42. !rankshaft position sensor.

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Fig. 1-43. istri"utor rpm sensor.

IN.ECTOR PULSE +I%TH

The injector pulse width indicates the amount of time each injector is energi


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#nder low load conditions! the computer will shorten the injector pulse width.

9ith the injectors being closed a large percentage of time! the air-fuel mixture will

be leaner for better fuel economy.

L#.ETRONIC FUEL IN.ECTION S(STEM

The %-Cetronic is an electronically controlled fuel injection system! which injects

fuel intermittently into the inta0e manifold ports.

The %-jetronic system uses airflow sensor! air flap types! which is connected to

variable resistor! to measure the amount of outside air entering the engine.

The %-jetronic system! Fig. -42! typically consists of"

Fuel delivery system 3electric fuel pump! fuel filter! fuel pressure regulator!

fuel injectors! cold start injector! fuel accumulator! and connecting lines and

hoses6.

Air induction system 3air filter! throttle valves! idle air bypass valve! and

connecting ducts6.

+ensor system 3airflow sensor! throttle position sensor! engine coolant

temperature sensor! inlet air temperature sensor! lambda sensor! and

distributor rpm sensor or cran0shaft position sensor6.

/omputer control system.

Operation

9hen the ignition switch is turned on and the engine is stationary! battery voltage

powers the $/# and the electric fuel pump through the relay. +ee Fig. -42. For

two seconds! the electric fuel pump draws the fuel from fuel tan0 at pressure of

approximately 1.2 bar 37= psi6 through a filter into the fuel rail. From the fuel rail!

fuel lines diverge to the injection valves 3injectors6 and to the cold start injector!

for initial engine start-up. After two seconds! the relay will cut off the circuit

between the battery and the electric fuel pump.

9hen the ignition switch is rotated to the start position and the engine is running!

the relay connects the circuit between the battery and the electric fuel pump.

9ith the engine running! the time during which the fuel injection valves remain

open is controlled by the signal from the $/#! which computes this time based

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on the signals received from the engine mounted sensors 3airflow sensor! inlet air

temperature sensor! distributor rpm sensor or cran0shaft position sensor! engine

coolant temperature sensor! throttle position sensor! and lambda sensor6.

Fig. 1-4. 7&etronic fuel in*ection system.

44

1.fuel tank0 2.Electric fuel pump0 3.Fuel filter0 4.istri"utor pipe0 5.Fuel pressureregulator0 6.!ontrol unit 8computer90 .n*ection ale 8in*ector90 #.!old start

in*ector0 $.idle&speed ad*usting scre'0 1%.(hrottle position sensor0 11.(hrottle

ale0 12.Airflo'0 13.elay com"ination0 14.lam"da sensor0 15.Enginetemperature sensor0 16.(hermo&time s'itch0 1.gnition distri"utor0 1#.dle air

"ypass ale0 1$.dle&miture ad*usting scre'0 2%.Battery0 21.gnition&starter

s'itch.


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L6#.ETRONIC FUEL IN.ECTION S(STEM

The %7-Cetronic fuel injection system has the same components of the %-Cetronic

fuel injection system but there is some difference between them.

The %7-jetronic differs from %-Cetronic in respect of the following details! see Fig.

-4= and Fig. -4@"

The control unit! which is suitable for installation in the engine

compartment! is attached to the airflow sensor and thus no longer re>uires

space in the passenger compartment.

The combined unit of control unit and airflow sensor with internal

connections simplifies the cable harness and reduces installation expense.

The use of digital techni>ues permits new function with improved

adaptation capabilities to be implemented as compared with the previous

analog techni>ues used.

Fig. 1-4!. 73&etronic fuel in*ection system.

45


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Fig.1-4". ntegration of E!: and airflo' sensor of the 73&etronic system.

LH#.ETRONIC FUEL IN.ECTION S(STEMThe %;-Cetronic is closely related to the %-Cetronic. The difference lies in the hot-

wire air-mass meter which measures the air mass inducted by the engine instead

of air flap types. +ee Fig. -4.

Fig. 1-4#. 7,&etronic fuel in*ection system.

MOTRONIC FUEL IN.ECTION S(STEM

46


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The (otronic fuel injection system uses an %-Cetronic system or %;-Cetronic

system coupled with an electronic ignition system! with both systems being

controlled by a common digital microcomputer. The same sensors can be used

for both the fuel injection and ignition8 thus more is achieved at a lower cost than

with two separate systems. +ee Fig. -45.

Fig. 1-4$. +otronic fuel in*ection system.

MULTI#POINT ELECTRONIC FUEL IN.ECTION S(STEM PRO'LEMS

4


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efective fuel pump.

irty injectors.

efective injectors.



efective sensors.


efective computer.


Hard Starting





efective fuel pump.

irty injectors.

efective injectors.

Air in the fuel lines.

efective engine coolant temperature sensor.

efective inlet air temperature sensor.

efective fuel accumulator.





efective lambda sensor.

4#


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efective injectors.

irty injectors.

efective engine coolant temperature sensor. efective inlet air temperature sensor.

Fuel lea0ing.

SIN$LE#POINT ELECTRONIC FUEL IN.ECTION S(STEM

+ingle-point electronic fuel injection system! is indirect injection system. This

means that the fuel is sprayed into the engine inta0e manifold ports.

+ingle-point electronic fuel injection system! has the injector no


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Operation

9hen the ignition switch is turned on and the engine is stationary! battery voltage

powers the $/# and the electric fuel pump through the relay. +ee Fig. -2D. For

two seconds! the electric fuel pump draws the fuel from fuel tan0 at pressure of

approximately 1.2 bar 37= psi6 through a filter into the fuel injector! for initial

engine start-up. After two seconds! the relay will cut off the circuit between the

battery and the electric fuel pump.

9hen the ignition switch is rotated to the start position and the engine is running!

the relay connects the circuit between the battery and the electric fuel pump.

9ith the engine running! the time during which the fuel injection valves remain

open is controlled by the signal from the $/#! which computes this time based

on the signals received from the engine mounted sensors 3airflow sensor! inlet air

temperature sensor! distributor rpm sensor or cran0shaft position sensor! engine

coolant temperature sensor! throttle position sensor! and lambda sensor6.

Fig. 1-%. (hrottle "ody in*ection system 8(B9.

Throttle ,o!- hou*in"

5%

!rankshaft positionsensor

Airflo' sensor

;ygen sensor

ntake manifold pressure

sensor

nlet air temperaturesensor

!oolant temperature sensor

(hrottle position sensor

Analy


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)t is a metal casting that holds injectors! fuel pressure regulator! throttle valves!

and other parts. +ee Fig. -2.

The T?) throttle body! li0e a carburetor body! bolts to the pad on the inta0e

manifold. Throttle plates are mounted in the lower section of the throttle body. A

lin0age mechanism or cable connects the throttle plates with the drivers gas

pedal. An inlet fuel line connects to one fitting on the throttle body. An outlet

return line to the tan0 connects to another fitting on the throttle body.

Throttle ,o!- in1ector

)t is a solenoid operated fuel valves mounted in upper section of throttle body

assembly. +ee Fig. -21.

A throttle body injector consists of an electric solenoid coil! armature or plunger!needle valve! needle seat! and injector spring.

9ires from the computer 3electronic control unit6 connect to the terminals on the

injectors. 9hen the computer energiuirt through the injector no


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Fig. 1-2. (hrottle "ody in*ector.

Throttle ,o!- fuel pre**ure re"ulator

)t is a spring-loaded bypass valve that maintains constant fuel pressure at

injectors. The throttle body fuel pressure regulator consists of a fuel valve!

diaphragm! and spring. +ee Fig. -27. 9hen fuel pressure is low 3initial engine

starting6! the spring holds the fuel valve closed. This causes pressure to build as

fuel flows into the regulator from the electric fuel pump.

9hen a preset pressure is reached! pressure acts on the diaphragm. The

diaphragm compresses the spring and opens the fuel valve. Fuel can then flow

bac0 to the fuel tan0. This limits the maximum fuel pressure at the injectors.

I!le air control ale

An idle air control valve is used in a T?) to help control engine idle speed. )t is a

solenoid operated air bypass valve. +ee Fig. -27. The system computer

normally opens and closes the idle air control valve.

9hen open! the idle air control valve allows more air to enter the inta0e manifold.

This tends to increase idle rpm. 9hen closed! the valve decreases bypass air

and idle speed. The valve can be used to control both slow and fast idle speeds.

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Throttle plate

)t is butterfly valves that control airflow through throttle body. +ee Fig. -27.

Fig. 1-3.Basic parts of (B.

Sen*or *-*tem

(onitors engine operating conditions and reports this information to the computer

3cran0shaft position sensor! airflow sensor! throttle position sensor! engine

coolant temperature sensor! inlet air temperature sensor! exhaust gas or oxygen

sensor! inta0e manifold pressure sensor! and distributor rpm sensor or cran0shaft

position sensor6.

Computer control *-*tem

The computer control system uses electrical data from the sensors to control the

operation of the fuel injectors. A wiring harness connects the engine sensors to

the input of the computer. Another wiring harness connects the output of the

computer to the fuel injectors.

MONO#.ETRONIC FUEL IN.ECTION S(STEM 3?osch /ompany6

(ono-Cetronic is an electronically controlled! single-point injection system for 4

cylinder engines. (ono-jetronic fuel injection system has the same components

of throttle body injection system 3T?)6! but the difference lies in the control of idle

speed.

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)n (ono-Cetronic fuel injection system! the position of throttle valve actuator 3idle

speed switch6 is closed to the throttle valve lever. +ee Fig. -24.

9hen the throttle valve actuator 3idle speed switch6 pushing the throttle valve

lever! this tends to increase idle speed of the engine.

Fig. 1-4. +ono&etronic fuel in*ection system.

54


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MONO # MOTRONIC FUEL IN.ECTION S(STEM 3?osch /ompany6

The (ono-(otronic fuel injection system has the same components of the (ono-

Cetronic fuel injection system but there is some difference between them.

(ono-(otronic fuel injection system coupled with an electronic ignition system!

with both systems being controlled by a common digital microcomputer. The

same sensors can be used for both the fuel injection and ignition8 thus more is

achieved at a lower cost than with two separate systems. +ee Fig. -22.

Fig. 1-. +ono&+otronic fuel in*ection system.

SIN$LE#POINT ELECTRONIC FUEL IN.ECTION S(STEM PRO'LEMS

55


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efective fuel pump.

irty injectors.

efective injectors.



efective sensors. efective computer.

efective throttle valve actuator 3idle speed switch6 in mono-jetronic fuel

injection system.

efective idle air control valve in throttle body injection system 3T?)6.


Hard Starting


injection system.



efective fuel pump.

irty injectors.

efective injectors.

Air in the fuel lines.



efective fuel accumulator in mono-jetronic fuel injection system.

56


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efective lambda sensor.


injection system.


efective injectors.

irty injectors.



Fuel lea0ing.

36559209 fuel system for gasoline engines 1

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