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© 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
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