© Goodheart-Willcox Co., Inc. by Russell Krick Publisher The Goodheart-Willcox Co., Inc. Tinley...

© Goodheart-Willcox Co., Inc.

by

Russell Krick

Publisher

The Goodheart-Willcox Co., Inc.Tinley Park, Illinois

Gasoline injection fundamentalsGasoline injection classificationsThrottle body and multiport injectionGasoline injection controlsElectronic fuel injectionEngine sensors

(18 Topics)

Throttle body injectionEngine idle speed controlContinuous throttle body injectionElectronic multiport injectionAir-fuel emulsion injector

Injector pulse width

Injector resistor packAirflow sensing multiport EFIPressure sensing multiport EFIHydraulic-mechanical continuous

injection systemFuel accumulator

Unitized multiport injection

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Provides the engine with the correct air-fuel mixture for specific operating conditions

Uses pressure from an electric fuel pump to spray fuel into the engine’s intake manifold

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AdvantagesImproved atomizationBetter fuel distributionSmoother idleImproved fuel economyLower emissionsBetter cold-weather driveabilityIncreased engine powerSimpler

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Atmospheric PressureFormed by the air surrounding the earthAt sea level, the atmosphere exerts

14.7 psi (103 kPa)

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Vacuum

Lower than atmospheric pressureLess than 14.7 psi (103 kPa) at sea

levelSometimes called suction

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Differences in Pressure Cause Flow

Engines use differences in pressure to force fuel and air into its cylinders

Engine acts as a vacuum pump, producing low pressure, or vacuum in the intake manifold

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Intake Manifold Vacuum

Closed throttle, high vacuum

Open throttle, reduced vacuum

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Engine Throttle ValveControls airflow

and gasoline engine power output

When opened, airflow, fuel flow, and power increase

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Drive-by-Wire SystemUses a pedal sensor, control module

and an actuator to operate the throttle valve on a gasoline engine

When the pedal is pressed, it moves a variable resistor

Control module senses pedal position by measuring current flow through the resistor, and sends a signal to the actuator, controlling engine speed

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There are many types of gasoline injection systems

A gasoline injection system is commonly called a fuel injection system

A diesel injection system is also a fuel injection system

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MultiportInjection

Gasoline is sprayed into each intake port, toward each intake valve

Throttle Body Injection

Injector nozzles in a throttle body

assembly on top of the engine

Direct Injection

Sprays fuel directly into engine combustion

chambers. Used in all diesel injection systems

Indirect Injection

Sprays fuel into intake manifold. Most gasoline

systems are indirect

Electronic fuel injectionHydraulic fuel injectionMechanical fuel injectionInjection timingInjector opening relationship

Electronic Fuel InjectionUses various engine sensors and a

control module to regulate injectionMost common type of gasoline injection

system

Hydraulic Fuel InjectionUses hydraulic control devices moved

by air of fuel pressureAirflow sensor and fuel distributor meter

gasoline (continuous injection)

Mechanical InjectionUses throttle linkage, mechanical pump,

and governor to control injectionUsed on older, high-performance, and

diesel applications

Intermittent InjectionOpens and closes injectors

independently of engine intake valvesAlso known as modulated injection

Timed InjectionSprays fuel just before, or as the intake

valves openA good example is diesel Injection

Continuous InjectionSprays fuel into intake manifold at all

timesAir-fuel ratio is controlled by increasing

or decreasing fuel pressure at the injectors

Injector Opening Relationship

Simultaneous InjectionAll the injectors open at the same timePulsed on and off together

Sequential InjectionInjectors open one after the otherInjection matches the firing order of the

engine

Injector Opening Relationship

Group InjectionSeveral, but not all injectors open at the

same timeV-8 engine–one group of injectors open at

one time, another group of four open at a different time

EFI system can be divided into four subsystems:fuel delivery systemair induction systemsensor systemcomputer control system

Electronic FuelInjection (EFI)

Systems Overview

Fuel Delivery System

ComponentsElectric fuel pumpFuel filterFuel pressure regulatorInjectors

Fuel Delivery System

Electric Fuel PumpDraws gasoline out of the tankForces it to the fuel railUnused fuel returns to the tank

Fuel Pressure Regulator

Controls pressure entering injector(s)Returns excess fuel to the tankVacuum may be ported into the

regulatorlower pressure at idleincreasing pressure at higher load

Fuel Pressure Regulator

Low vacuum,high load

High vacuum,low load

Injectors

Solenoid-operated fuel valve

When current flows, magnetism attracts armature to open injector

Electrical terminals

Armature

Injector body

Needle valve

Fuel inlet

Inlet screen

Return spring

Coil windings

Spray mist

Air Induction SystemAir filter

traps dust and debrisThrottle valve(s)

controls airflow through throttle bodySensors

sense airflow and throttle positionDucts

route clean air to throttle body

Air Induction SystemThrottle plates control airflow

Sensor SystemInputs to the control moduleSignal the following operating

conditions:temperaturepositionpressure or vacuumspeed

Computer Control System

Uses data from the sensors to

control fuel injectors

Wiring harness connects

computer to sensors and

injectors

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Electronic Control Module

Commonly mounted behind the instrument

panel

Exhaust gas oxygenManifold absolute pressure (MAP)Throttle position (TP)Engine coolant temperature(ECT)AirflowInlet air temperature (IAT)Crankshaft position (CKP)

Oxygen Sensor

Measures oxygen content in the exhaust

Threaded into exhaust manifold before the catalytic converter

OBDII equipped vehicles also use a second sensor after the catalytic converter to monitor converter efficiency

Oxygen SensorSignals air-fuel mixture

Oxygen Sensor Operation

Increase in exhaust oxygen from lean mixture causes oxygen sensor voltage to increase

Decrease in exhaust oxygen from rich mixture causes oxygen sensor voltage to decrease

Oxygen Sensor Construction

Open LoopInjection system does not use exhaust gas

oxygen as an indicator of air-fuel mixtureOperation is from information stored in the

computerCold engines operate in open loop

Closed LoopComputer uses exhaust oxygen as a main

input for air-fuel mixture controlNormally, hot engines operate in closed loop

Information Flow

Open Loop Closed Loop

Map Sensor

Senses engine load by measuring pressure or vacuum inside the intake manifold

High pressure (low vacuum) indicates high load

Low pressure (high vacuum) indicates low load

Map SensorOften mounted on the engine or in the

engine compartment

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MAP Sensor TheoryPiezo-resistor chip converts pressure

change into resistance change

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MAP Sensor Side ViewManifold vacuum flexes the chip,

altering its resistance

Throttle Position Sensor

Senses throttle positionVariable resistor connected to the

throttle plateAs the throttle opens, sensor resistance

changes, signaling throttle position

Throttle Position Sensor

Variable resistor signals throttle position

Engine Coolant Temperature Sensor

Senses engine coolant temperatureAt low temperature, sensor resistance

may be high, signal voltage high, computer will richen mixture

At high temperature, sensor resistance may be low, signal voltage low, computer will deliver leaner mixture

Airflow Sensor

Measures amount of air entering engineAir flap or door operates a variable

resistorAirflow opens the flap, changing

position of the variable resistor, changing the signal voltage to the computer

Airflow Sensor Operation

Airflow sensor operates a variable resistor

Inlet Air Temperature Sensor

Measures temperature of air entering the engine

Air temperature affects air densityCooler air is more dense, requiring

more fuelOperation is similar to engine coolant

temperature sensor

Crankshaft Position Sensor

Detects engine speed and positionInformation is used by computer for

ignition timing and fuel injection operation

Other Sensors

Several other sensors may be used:A/C compressor sensortransmission sensorEGR sensorvehicle speed sensorknock sensor

Digital Signals

Signal is on or offVoltage goes from maximum to

minimum instantly, like a switchCrankshaft position sensor output may

be a digital signal

Analog Signals

Signal varies in voltage or strengthMay be produced by change in

resistance of a sensor, sensing changes in temperature, pressure, or position

Pulse width is the time injector is energized

At wide open throttle, computer lengthens injector pulse to richen mixture

At low load, computer shortens pulse width

Injector Pulse Width

Injector Pulse Width

Pulse width controls the amount offuel injected

Components:throttle body housingTBI injectorTBI pressure regulatoridle speed controlthrottle position sensorthrottle plates

TBI Overview

TBI Assembly

Fuel enters the regulator before passing into the

injector

Throttle Body Housing

Bolted to the intake manifoldInjector(s) are in the upper housingThrottle plates are in the lower housingHolds the throttle position sensor, fuel

pressure regulator and idle speed control device

TBI Injector

Components:solenoid coilarmature or plungerball or needle valveseat

TBI Injector

This injector uses a ball-type valve

instead of a pointed needle

valve

Injector Operation

When the computer energizes the injector, a magnetic field is produced in the coil

Magnetism pulls the plunger and valve up to open the injector

Fuel is sprayed above the throttle valve

TBI Pressure Regulator

Contains a fuel valve, diaphragm and spring

Spring holds the fuel valve closed, causing pressure increase as fuel flows in from the electric fuel pump

When preset pressure is reached, fuel pressure acting on the diaphragm forces the fuel valve open, allowing fuel to flow back to the tank

TBI System Cutaway

There are several different types of idle speed control devices:fast idle thermo valveidle air control motorthrottle positioner

Fast Idle Thermo Valve

Thermowax plunger contracts when cold to allow more airflow at idle

Plunger expands when the engine warms, closing valve, reducing airflow

Idle air control valve and the

thermo valve affect air that bypasses

the throttle valve to alter idle speed

Fast Idle Thermo Valve

Idle Air Control MotorComputer controlled solenoid or

servomotor-operated air bypass valve

Throttle Positioner

Computer controlled motor opens or closes the throttle plates to control idle speed

In this way, the computer can maintain a precise idle speed with changes in temperature, load and other conditions

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Sprays a solid stream of fuel into the air horn

Does not pulse the injectors on and off to control the air-fuel mixture

System alters pressure applied to the throttle body nozzles to control mixture

Continuous ThrottleBody Injection (CTBI)

Uses a computer, sensors and one solenoid injector for each cylinder

Components:multiport throttle bodymultiport pressure regulatorfuel rail

Multiport Fuel InjectionControls

Multiport Fuel InjectionAir Delivery

Multiport Fuel InjectionFuel Delivery

Injection ComponentsThrottle body

contains throttle plates and a throttle position sensor

Multiport pressure regulatormounted on the fuel rail, maintains

pressure at the inlet to the injectors by acting as a bypass

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Fuel railconnects the main fuel line to the inlet

of each injector

Multiport fuel Injectorsprays fuel into the intake port, below

the throttle valve

Injection Components

Injection Components

Injection Components

Multiport Fuel Injector

Solenoid opens the injector when current flows

through the coil

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Mixes air with the fuel creating a slurrySlurry is injected into the intake

manifoldAtomizes the fuel and improves

combustionLow pressure air from the air injection

pump may be used

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Mounts all of the injectors into a single assembly

Plastic transfer lines carry fuel from each injector to a poppet valve located in the intake port

Fuel injection transfer lines connect each injector to its poppet valve

Fuel injection poppet valve spring loaded valve prevents fuel leakage

between injector pulses when the fuel injector opens, fuel pressure

forces the poppet valve open, spraying fuel into the intake port

Components

Components

Fuel injection transfer linesconnect each injector to its poppet valve

Fuel injection poppet valvespring loaded valve prevents fuel leakage

between injector pulseswhen the fuel injector opens, fuel pressure

forces the poppet valve open, spraying fuel into the intake port

Unitized Injector

Note the fitting for the plastic transfer line

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Set of low-ohm resistorsControl current flow to each injector coilProtect windings from excess currentUsually 5-7 ohmsOften mounted in the engine

compartment

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Injector Circuit

Circuit contains resistor pack

Each pin corresponds to a resistor

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Uses an airflow sensor as a main control

Airflow sensor is placed at the inlet to the intake manifold

Sensor converts airflow into a signal for the computer

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System Overview

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Airflow Sensor Operation

Throttle almost closed, sensor

detects little airflow

Throttle moved open for more power, increased flow

pushes sensor flap open

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Uses intake manifold pressure (vacuum) as a primary control

Pressure sensor is connected to the intake manifold

Sensor converts changes in manifold pressure into changes in resistance

Computer uses this data

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System Overview

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Continuous Injection System (CSI)

Hydraulic-mechanical systemMixture control unit senses airflow with

an airflow sensor plate and distributes fuel

Operates the injectors with a fuel distributor

Continuous Injection System (CSI)

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Airflow SensorDisc-shaped plate, hinged in the air

hornPlate operates a lever armLever arm pushes up a fuel control

plunger in the fuel distributor when air flows

Plunger opens fuel passages to the injectors

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CIS Fuel Distributor

Hydraulically-operated valve mechanismControls fuel flow or pressure to each

injectorWhenever air flows to the engine, the

fuel distributor sends fuel to the injectors, causing them to spray continuously

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CIS Operation

Airflow sensor

Idle, low airflow

Partial load, more airflow

Full load, airflow pushes plate up high

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Continuous Fuel Injector

Spring-loaded valveOne injector for each cylinderInjects fuel continuously when the

engine is runningSpring holds the valve closedFuel pressure forces it open, spraying

fuel into the intake portSpring-loaded valveFuel pressure forces the valve open

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Continuous Fuel

Injector

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Cold Start InjectorExtra fuel injectorSprays fuel into the intake plenum for

cold engine starting and runningImproves cold operation by enriching

the air-fuel mixtureControlled by a thermo-time switch or

control module

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Cold Start Injector

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Damps pressure pulsesMay maintain pressure when shut down

to aid restarting

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Fuel Accumulator Components and Operation

Engine running, fuel pressure compresses

diaphragm spring

Engine off, spring pressure on diaphragm maintains

system pressure