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Heat from an electric spark produced by the ignition system sets fire to, or ignites, the air-fuel mixture.. In the diesel or compression-engine, the fuel mixes with air after it enters

11.1 INTERNAL COMBUSTION ENGINE

An engine (Fig 11-1) is a machine that converts heat energy into

mechanical energy The heat from burning a fuel produces power which moves the vehicle.Sometimes the engine is called the power plant.

Automotive engines are internal-combustion(IC) engines because the fuel that runs them is burned internally, or inside the engine There are two types: reciprocating and rotary (Fig 11-2) Reciprocating means moving up and

down, or back and forth Most automotive engines are reciprocating Theyhave piston that move up and down, or reciprocate, in cylinder (Fig.11-3)

These are piston engines.

Rotary engines have rotors that spin, or rotate The only such engine now used in automobiles is the Wankel engine (12-7).

PISTON ENGINE BASICS

11-2 TWO KINDS OF PISTON ENGINES

The two kinds of piston engines are the spark-ignition engine and the

compression-ignition(diesel) engine The differences between them are:

• The type of fuel used

• The way the fuel gets into the cylinders

• The way the fuel is ignited

The spark-ignition engine usually runs on a liquid fuel such as gasoline

or alcohol blend The fuel must be highly volatile so that it vaporizes quickly.

The fuel vapor mixes with air before entering the engine cylinders This forms

the highly combustible air-fuel mixture that burns easily The mixture then

enters the cylinders and is compressed Heat from an electric spark produced

by the ignition system sets fire to, or ignites, the air-fuel mixture As the mixture burns (combustion), high temperature and pressure are produced in

the cylinder (9-9) This high pressure, applied to the top of the piston, forces it

to move down the cylinder The motion is carried by gears and shafts to thewheels that drive the car The wheels turn and the car moves

In the diesel or compression-engine, the fuel mixes with air after it

enters the engine cylinders The piston compresses the air to as 1/22 of itsoriginal volume Compressing the air this much raises its temperature to1000°F (538°C) or higher A light oil called diesel fuel is then sprayed or

injected into the hot air The hot air or heat of compression ignites the fuel.

The method of ignition–by heat of compression–give the diesel engine thename compression-ignition engine

11-15 Basic engine systems

A spark-ignition engine requires four basic systems to run A dieselengine requires three of these systems They are :

Figure 11-20 shows one type of fuel system used with spark-ignition

engines The fuel tank holds a supply of fuel A fuel pump sends fuel from the tank to the fuel injectors These are valves controlled by an electronic control module ( ECM ), or computer.

1 Fuel tank: The fuel tank is made of sheet metal, fiberglass, or plastic It has two main openings Fuel is pumped in through one

opening and out through the other

2 Fuel pump: Figure 11-20 shows the fuel pump inside the fuel tank

.This is the arrangement used in most vehicles with electronic fuelinjection An electric motor operates the fuel pump

3 Fuel injectors: fuel injectors, or fuel-injection valves are

fluid-control valves They are either open or closed .The fuel pumpsends fuel under constant pressure to the injectors On thesystem shown in Fig 11-20, each cylinder receives fuel from its

own injector.This is a port injection system At the proper time for

fuel delivery, the ECM turns on each injector This opens the valve

in the end of the injector The pressurized fuel then sprays out intothe air entering the cylinder

Fuel delivery continues as long as the valve is open Thetime is computed and controlled by the ECM When the properamount of fuel has sprayed out , the ECM turns off the injector The valve closes and fuel delivery stops

Another fuel-injection system uses one or two injectorslocated above the throttle valve (Fig 1-13) They feed the properamount of fuel to the air entering the intake manifold This is

throttle-body injection (TBI)

In the past, carburetors (chap.21) were part of most fuel

systems Carburetors are mixing devices Air passing through thecarburetor picks up and mixes with the fuel to provide a

combustible mixture Most vehicles now have fuel-injectionsystems.

11-17 Electric ignition system

The fuel system delivers a combustible mixture to each cylinder The

upward movement of the piston compresses the mixture Then the ignition system (Fig 11-21) delivers an electric spark to the spark plug in that cylinder.

The spark ignites the compressed air-fuel mixture and combustion follows

The ignition system takes the low voltage of the battery (12 volts) andsteps up the voltage as high as 47000 volts ( or higher ) in some systems.This high voltage produces sparks that jump the gaps in the spark plugs Thehot sparks ignite the compressed air-fuel mixture

11-18 Lubricating system

The engine has many moving metal parts When metal parts rub against

each other, they wear rapidly To prevent this, engines have a lubricating system that floods moving parts with oil (Fig 11-22) The oil gets between the

moving metal parts so they slide on the oil and not on each other

The lubricating system has an oil pan at the bottom of the engine that holds several quarts ( liters) of oil An oil pump, driven by the engine, sends oil

from this reservoir through the engine After circulating through the engine, theoil drops back down in to the oil pan The oil pump continues to circulate theoil as long as the engine runs

11-19 Cooling system

Where there is the fire ( combustion ), there is heat Burning the air-fuelmixture raises the temperature inside the engine cylinder several thousanddegrees Some of this heat produces the high pressure that cause the pistons

to move

Some heat leaves the cylinder in their exhaust gas This is the remains

of the air-fuel mixture after it burns in the cylinders The exhaust strokes clearout the exhaust gas The lubricating oil also removes some heat The oil getshot as it flows through the engine Then the oil drops into the oil pan and coolsoff

The engine cooling system ( Fig 11-23) removes the rest of the heat The engine has open spaces or water jackets surrounding the cylinders A mixture of water and antifreeze, called coolant, circulates through the water jackets The coolant picks up heat and carries it to the radiator at the front of

the car Air passing through the radiator picks up the heat and carries it away

This action prevents the engine from getting too hot or overheating.

11-20 Other engine systems

An engine will run with the four basic systems described above-fuel,ignition, lubricating, and cooling For use in the car, the engine requires three

other related systems There are the exhaust system, the emission-control system, and the starting system.

The exhaust system reduces the noise of the burned gases leaving thecylinders Also, it carries the exhaust gases and excess heat safely away fromthe passenger compartment

The emission-control system reduces the air pollution from the vehicle

and the engine The starting system cranks and starts the engine A battery

provides the electric power to operate the starting motor and the ignitionsystem during cranking Later chapters describe these systems

12-11 Firing order

The firing order is the sequence in which the cylinders deliver their

power strokes It is designed into the engine The crankpin and camshaftarrangement determine the firing other In most engines, the firing orderevenly distributes the power strokes along the crankshaft ( Fig 12-20) Mostengine designs avoid firing two cylinders, one after the other , at the sameend of the crankshaft

Firing orders for the same type of engine may differ Two firing orders forin-line four-cylinder engines are 1-3-4-2 and 1-2-4-3 In-line six-cylinderengines use 1-5-3-6-2-4 (fig 12-20) A Chrysler V-6 and two General Motors V-

6 engines (fig 12-19) all have the same firing order of 1-2-3-4-5-6 Ford V-6engines have fired 1-4-2-5-3-6 and 1-4-2-3-5-6 A firing order used on V-8engines by Chrysler and General Motors is 1-8-4-3-6-5-7-2 ( fig 12-20) FordV-8 engines use 1-5-4-2-6-3-7-8 and 1-3-7-2-6-5-4-8

Many engine service jobs require that you know the cylinder numberingand firing order Some engines have cylinder numbering identification, firingorder, and direction of ignition-distributor rotation cast into or imprinted on theintake manifold The information is also in the manufacturer’s service manual

The complete firing order of a four-cycle engine represents twocomplete revolutions of the crankshaft This is 720 degrees of crankshaftrotation Most engines are “even firing “ This means, for example, that is anin-line six-cylinder engine a firing impulse occurs every 120 degrees ofcrankshaft rotation (720 ÷ 6 = 120) The firing order of this engine is 1-5-3-6-2-

4 When piston number 1 is at TDC on the end of the compression stroke,piston number 6 is at TDC on the end of the exhaust stroke To determine the

two pistons that are moving up and down together ( piston pairs ), divide the

firing order in half Then place the second half under the first half :

1-5-3

The piston pairs for this inline six-cylinder engine are 1 and 6 , 5 and 2,

3 and 4

19-1 Introduction to gasoline fuel-injection systems

Most 1980 and later cars have an electronic engine control (EEC)

system It controls the ignition and fuel-injection systems The basic operation

of electronic engine controls is described in chap 10

The fuel-injection system supplies the engine with a combustible air-fuelmixture It varies the richness of the mixture to suit different operatingconditions When a cold engine is started, the fuel system delivers a very richmixture This has a high proportion of fuel After the engine warms up, the fuelsystem “ leans out “ the mixture It then has a lower proportion of fuel Foracceleration and high speed, the mixture is again enriched

There are two types of gasoline fuel-injection systems:

1 Port fuel injection (PFI) which has an injection valve or fuel injector in each intake port (fig 19-1).

2 Throttle-body fuel injection (TBI) in which one or two fuel

injectors are located above the throttle valves ( fig 19-2)

With either system, the electric fuel pump supplies the fuel injectors withfuel under pressure As soon as the injector opens, fuel sprays out ( fig 19-3 )

An electric solenoid in the injection opens and closes the valve The solenoid

has a small coil of wire that becomes magnetized when the voltage is applied( fig 19-4 ) The magnetism lifts the armature which raises the needle valve orpintle off its seat Fuel sprays out as long as the pintle is raised When thevoltage stops, the coil loses its magnetism The closing spring pushes the

pintle back down onto its seat This stops the fuel spray Each opening and

closing of the injector pintle is an injector pulse

Note : some injectors use a ball valve instead of a needle valve.

Operation of the ball-type injector is basically the same as described above

19-3 Electronic fuel injection

Figure 10-19 shows the components of an electronic fuel injection (EFI)

system Most fuel-injection systems are electronically controlled The

controller is an electronic control module (ECM) or electronic control unit

(ECU) It is also called an “ on-board computer“ because it is “on-board“ thecar

Various components of the engine and fuel system send electric signals

to the ECM (fig 19-5) The ECM continuously calculates how much fuel to

inject It then opens the fuel injectors so the proper amount of fuel sprays out

to produce the desired air-fuel ratio

19-6 Air and fuel metering

The fuel system must accurately measure or meter the air and fuel

entering the engine This produces the proper air-fuel ratio to make acombustible mixture A mixture that is too lean (not enough fuel in it) will notburn and produces excessive pollutants A mixture that is too rich (excess fuel

in it) will also produce excess pollutants Figure 19-8 shows how mixturerichness affects engine power As the mixture becomes leaner, power falls off

The electronic engine control system includes the ECM and various

sensing devices or sensors that report to it A sensor is a device that receives

and reacts to a signal This may be a change in pressure, temperature, orvoltage Some sensors report the amount of air entering The ECM thencalculates for how long to open the injectors

19-7 Operaion of fuel-injection systems

Sensors that report to the ECM include ( fig 19-5)

• Engine speed

• Throttle position

• Intake-manifold vacuum or manifold-absolute pressure (MAP)

• Engine coolant temperature

• Amount and temperature of air entering engine

• Amount of oxygen in exhaust gas

The opening and closing of an injector is its duty cycle How long the ECM signals the injector to remain open is the injector pulse width Figure 19-

9 shows how varying the pulse width varies the amount of fuel injected.Suppose more fuel is needed because the throttle has been opened foracceleration and more air is entering Then the ECM increases the pulsewidth This holds the injectors open longer each time they open to provide theadditional fuel

Note: The system described above is a pulsed fuel-injection system.

The injectors open and close (pulse) The continuous-injection system (CIS) is

another type of fuel-injection system It is used a few vehicles The injectors

are open continuously Changing the pressure applied to the fuel varies theamount of fuel injected

19-12 Indirect measurement of air flow

Information about engine speed and engine load can be tell the ECMhow much air is entering the engine Using this information to regulate fuel

feed is called speed-density metering It is used in fuel-injection systems that

do not directly measure mass air flow The speed is the speed of the engine.

The density is the density of the air or air-fuel mixture in the intake manifold

Throttle position (engine speed) and intake-manifold vacuum (engineload) measure air flow indirectly Intake manifold vacuum is continuouslymeasured by a sensor that changes vacuum (or absolute pressure) into avarying voltage signal The ECM combines this with the TPS signal todetermine how much air entering Inputs from other sensor may cause theECM to modify this calculation (fig 19-5 ) Engine speed (instead of throttleposition) and intake-manifold vacuum can also tell the ECM how much air isentering the engine

19-13 Measuring intake-manifold vacuum (manifold absolute pressure)

Intake-manifold vacuum is measured in two ways ( fig 19-19 ):

1 With a vacuum gauge

2 With a manifold absolute pressure (MAP) gauge

The two gauges are basically the same Both have a flexible diaphragmthat separates the two chambers in the gauge The difference is that onechamber of the vacuum gauge is open to the atmosphere One chamber ofthe absolute-pressure gauge contains a vacuum (fig 19-19) The vacuumgauge compares atmospheric pressure with intake-manifold pressure In anaturally-aspirated engine, manifold pressure is less than atmosphericpressure A vacuum gauge measures this partial vacuum in the intake-manifold

The manifold absolute-pressure (MAP) gauge compares the actualpressure in the intake manifold with a vacuum This is more accurate than thevacuum gauge which compares intake manifold vacuum with atmosphericpressure The vacuum gauge is less accurate because atmospheric pressurevaries

Vacuum and pressure sensor are not constructed exactly like thegauges described above But their operation is basically the same Most

electronic engine control systems include a manifold-absolute pressure (MAP)

sensor (figs 10-19 and 19-20 ) It senses the pressure (vacuum) changes in

the intake manifold This information is sent as a varying voltage signal to theECM

19-14 Direct measurement of air flow

Four methods of measuring air flow directly are vane, air-flow sensor plate, hot-wise induction, and heated film Each continuously measures the actual amount of air flowing through the air-flow meter (fig 19-21) This

information is then sent to the ECM

1 vane : The vane type air-flow meter is used in some pulsed

fuel-injection systems such as the Bosch L system (fig 19-21) Thespring-loaded vane is in the air-intake passage of the air-flowmeter Air flowing through forces the vane to swing The more air,the farther the vane swings A vane-position sensor works like therotary throttle-position sensor Depending on its position, it sendsvarying voltage signals to the ECM This tells the ECM how muchair is flowing through The ECM then adjusts fuel flow to match

2 Air-flow sensor plate : The air flow sensor plate is used in

mechanical continuous-injection systems (fig 19-14) The plate is

in the intake-air passage of the air-flow meter As air flowincreases, the plate moves higher This lifts a control plunger inthe fuel distributor to allow more fuel flow to the injectors Theadded fuel flow matches the additional air flow

3 Hot-wire induction : A platinum wire is in the path of the incoming

air through the air-flow meter The wire is kept hot by an electriccurrent flowing through it However, the air flow cools the wire Themore air that passes through the air-flow meter, the more heat that

is lost from the wire

The system keeps the wire at a specific temperature byadjusting current flow If more air flows through and takes moreheat from the wire , the system sends more current through Thismaintains the temperature The amount of current required istherefore a measure of how much air is flowing through The ECMreads this varying current as air flow

4 Heated film :The heated film consists of metal foil or nickel grid

coated with a high-temperature material (fig19-22) Current flowingthrough the film heats it Air flowing past the film cools it Like theheated wire, the system maintains the film at a specifictemperature The amount of current required is a measure of airflow

19-15 Atmospheric-pressure and air-temperature sensors

Changing atmospheric pressure and air temperature change the density

of the air Air that is hot and at low atmospheric pressure is less dense It

contains less oxygen than an equal volume of cooler air under higheratmospheric pressure When the amount of oxygen entering the enginevaries, so does the amount of fuel that can be burned

Some systems include an atmospheric-pressure sensor It is also calledthe barometric-pressure sensor or BARO sensor It is similar to the MAPsensor However, the barometric-pressure sensor reads atmosphericpressure The air-temperature sensor (fig 19-23) is a thermistor Its electricalresistance decreases as its temperature increases Figure 19-21 shows itslocation in the vane-type air-flow meter Both types of sensors send varyingvoltage signals to the ECM so it knows the atmospheric pressure and airtemperature

21-1 Purpose and types of carburetors:

The carburetor (fig 21-1) is a mixing device that supplies the engine with

a combustible air-fuel mixture Figure 21-2 shows the three basic parts of a

fixed-venturi carburetor.These are the air horn, the float bowl, and the throttle

body

The venturi is a restricted space through which the air entering theengine must pass The air movement produces a partial vacuum in the

venturi This is called venturi vacuum The resulting pressure differential

causes fuel to discharge from the fuel nozzle into the intake air (fig 21-3).Thisproduces the air-fuel mixture for the engine

Some carburetors have a variable-venturi These are described in

21-28

23-1 Diesel engines

Diesel engines are similar to spark-ignition engines in construction Bothhave pistons, with piston rings, moving up and down in cylinders Both burnfuel in combustion chambers in the upper part of the cylinders The highpressure produced by the burning fuel pushes the pistons down This rotatesthe crankshaft and the rotary motion is carried through shafts and gears to thedrive wheels Diesel and spark-ignition engine are compared in 11-2

23-2 Diesel-engine operation

Figure 23-1 shows the four piston strokes in a four-stroke-cycle dieselengine

1 Intake stroke : The diesel engine takes in air alone No throttle

valve impedes the airflow In the spark-ignition engine, a mixture

of air and fuel enters the engine cylinders on the intake stroke.The throttle valve controls the amount that enters

2 Compression stroke :In the diesel engine , the upward-moving

piston compresses air alone On the other hand, in the ignition engine, the piston compresses the air-fuel mixture

spark-3 Power stroke : In the diesel engine, a light oil called diesel fuel is

sprayed (injected) into the compressed and hot air The heat of compression ignites the fuel In the spark-ignition engine, a spark

at the spark plug ignites the compressed air-fuel mixture

4 Exhaust stroke : The exhaust stroke is the same for both

engines The exhaust valve opens and the burned gases flow out

as the piston moves up the cylinder

23-3 Diesel-engine characteristics

The diesel engine has the following characteristics:

1 No throttle valve (except some engines with the pneumatic

governor described in 23-12 ).

2 Compresses only air on the compression stroke.

3 Heat of compression ignites fuel as it sprays into the engine

cylinders

4 Has a high compression ratio of 16:1 to 22:1.

5 Controls engine power and speed only by the amount of fuel

sprayed into the cylinders More fuel equals more power

6 Has glow plugs or an electric intake-manifold heater to make

starting easier

25-1 Heat in the engine

The burning air-fuel mixture in the engine cylinders may reach 4000 oF(2200 oC) or higher This means engine parts get hot However, cylinder wallsmust not get hotter than about 500 oF (260 oC) Higher temperatures causelubricating oil to break down and lose its lubricating ability Other engine partsare also damaged To prevent over-heating, the cooling system removes theexcess heat (fig 15-14) This is about one-third of the heat produced in thecombustion chambers by the burning air-fuel mixtrure

25-2 Purpose of cooling system

The cooling system (figs 11-23 and 25-1) keeps the engine at its mostefficient temperature at all speeds and operating conditions Burning fuel inthe engine produces heat Some of this heat must be taken away before itdamages engine parts This is one of the three jobs performed by the cooling

system It also helps bring the engine up to normal operating temperature as

quickly as possible In addition, the cooling system provides a source of heat

for the passenger-compartment heater- and-air-coditioner.

27-1 The automotive electrical system

The automotive electrical system (fig 27-1) does several jobs Itproduces electric energy (electricity ) in the anternator It stores electricenergy in chemical form in the battery And it delivers electric energy fromthese sources on demand to any other electrical component in the vehicle

The electric energy cranks the engine to start it, supplies the sparks thatignite the air-fuel mixture so the engine runs, and keeps the battery charged.These are the jobs performed by the battery, starting, charging, and ignitionsystems Other electric and electronic devices and systems on the vehicleinclude :

a Electronic engine control systems and other electronic systemscontrolled by an electronic control module (ECM) or computer.These may include an electronic automatic transmission ortransaxle, power train, brakes, traction control, steering,suspension, air conditioning, and other components that operateunder varying conditions

b Signaling and accessory systems These include the lights, horn,instrument-panel indicators, service monitor systems, and otherdriver information systems Also included are the heater and airconditioner, and the radio and tape player

c Various motors that operate the seats, windows, door locks, trunklid, and windshield wipers and washers

All these components use electric current and voltage All may becomputer controlled And all are connected by insulated wires and the ground-return system Chapter 10 describes basic electricity and the one-wiresystem Chapter 19 describes electronic fuel injection and engine controlsystem components Separate chapters cover the battery, starting, charging,and ignition systems Chapter 34 describes other electronic devices

31-1 Purpose of ignition system

The purpose of the ignition system (figs 11-21 and 31-1) is to ignite thecompressed air-fuel mixture in the engine combustion chambers This shouldoccur at the proper time for combustion to begin To start combustion, theignition system delivers an electric spark that jumps a gap at the combustion-

chamber ends of the spark plugs The heat from this arc ignites the

compressed air-fuel mixture The mixture burns, creating pressure thatpushes the piston down the cylinders so the engine runs

The ignition system may be either a contact-point ignition system or an electronic ignition system This chapter describes the contact-point ignition system Chapter 32 covers electronic ignition systems Ignition system

trouble-diagnosis and service are covered in chap 33

31-3 Producing the spark

The ignition system consists of two separate but related circuits: the

low-voltage primary circuit and the high-voltage secondary circuit The ignition

coil (fig 31-1) has two windings The primary winding of few hundred turns ofheavy wire is part of the primary circuit The secondary winding of manythousand turns of fine wire is part of the secondary circuit When the ignition

key is ON and the contact points closed, current flows through the primarywinding(fig 31-7) This produces a magnetic field around the primary windings

in the coil

When the contact points open, current flow stops and the magnetic fieldcollapses As it collapses, it cuts across the thousands of turns of wire in thecoil secondary winding This produces a voltage in each turn These addtogether to produce the high voltage delivered through the secondary circuit tothe spark plug (fig 31-5)

31-7 Advancing the spark

When the engine is idling, the spark is timed to reach the spark plug justbefore the piston reaches TDC on the compression stroke At higher speeds,the spark must occur earlier If it does not, the piston will be past TDC andmoving down on the power stroke before combustion pressure reaches itsmaximum The piston is ahead of the pressure rise which results in weakpower stroke This wastes much of the energy in the fuel

To better use the energy in the fuel, the spark takes place earlier as

engine speed increases This sprake advance causes the mixture to burn

producing maximum pressure just as the piston moves through TDC Mostcontact-point distributors have two mechanisms to control spark advance A

centrifugal-advance mechanism adjusts the spark based on the engine speed.

A vacuum-advance mechanism adjusts the spark based on engine load On

the engine, both work together to provide the proper spark advance for theengine operating conditions

31-8 Centrifugal advance

The centrifugal advance mechanism advances the spark by pushing thebreaker cam ahead as engine speed increases Two advance weights, twoweight springs, and a cam assembly provide this action The cam assemblyincludes the breaker cam and an oval-shaped advance cam (fig 31-11) At lowspeed, the springs hold the weights in As engine speed increases, centrifugalforce causes the weights to overcome the spring force and pivot outward (fig31-12) This pushes the cam assembly ahead The contact points open andclose earlier, advancing the spark

31-9 Vacuum advance

When the throttle valve is only partly open, a partial vacuum develops inthe intake manifold Less air-fuel mixture gets into the engine cylinders.Thenthe fuel burns slower after it is ignited The spark must be advanced at partthrottle to give the mixture more time to burn

The vacuum-advance mechanism (figs 31-8 and 31-13) advances sparktiming by shifting the position of the breaker plate The vacuum-advance unit