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Chapter 22
Gasoline Injection Fundamentals
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Contents
(18 Topics)

• Gasoline injection fundamentals
• Gasoline injection classifications
• Throttle body and multiport injection
• Gasoline injection controls
• Electronic fuel injection
• Engine sensors

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Contents

• Injector pulse width

• Throttle body injection
• Engine idle speed control
• Continuous throttle body injection
• Electronic multiport injection
• Air-fuel emulsion injector

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Contents

• Unitized multiport injection

• Injector resistor pack
• Airflow sensing multiport EFI
• Pressure sensing multiport EFI
• Hydraulic-mechanical continuous injection system
• Fuel accumulator

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Gasoline Injection Fundamentals

• Uses pressure from an electric fuel pump to spray
  fuel into the engines intake manifold

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

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Advantages

• Improved atomization
• Better fuel distribution
• Smoother idle
• Improved fuel economy
• Lower emissions
• Better cold-weather driveability
• Increased engine power
• Simpler

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Atmospheric Pressure

• Formed by the air surrounding the earth
• At sea level, the atmosphere exerts 14.7 psi (103
  kPa)

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Vacuum

• Lower than atmospheric pressure
• Less than 14.7 psi (103 kPa) at sea level
• Sometimes 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
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Engine Throttle Valve

• Controls airflow and gasoline engine power output
• When opened, airflow, fuel flow, and power
  increase

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Drive-by-Wire System

• Uses 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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Gasoline Injection Classifications

• 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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Throttle Body and Multiport Injection
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Gasoline Injection Controls

• Electronic fuel injection
• Hydraulic fuel injection
• Mechanical fuel injection
• Injection timing
• Injector opening relationship

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Electronic Fuel Injection

• Uses various engine sensors and a control module
  to regulate injection
• Most common type of gasoline injection system

Hydraulic Fuel Injection

• Uses hydraulic control devices moved by air of
  fuel pressure
• Airflow sensor and fuel distributor meter
  gasoline (continuous injection)

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Mechanical Injection

• Uses throttle linkage, mechanical pump, and
  governor to control injection
• Used on older, high-performance, and diesel
  applications

Intermittent Injection

• Opens and closes injectors independently of
  engine intake valves
• Also known as modulated injection

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Timed Injection

• Sprays fuel just before, or as the intake valves
  open
• A good example is diesel Injection

Continuous Injection

• Sprays fuel into intake manifold at all times
• Air-fuel ratio is controlled by increasing or
  decreasing fuel pressure at the injectors

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Injector Opening Relationship

• Simultaneous Injection
• All the injectors open at the same time
• Pulsed on and off together
• Sequential Injection
• Injectors open one after the other
• Injection matches the firing order of the engine

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Injector Opening Relationship

• Group Injection
• Several, but not all injectors open at the same
  time
• V-8 engineone group of injectors open at one
  time, another group of four open at a different
  time

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Electronic FuelInjection (EFI)

• EFI system can be divided into four subsystems
• fuel delivery system
• air induction system
• sensor system
• computer control system

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Systems Overview
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Fuel Delivery System

• Components
• Electric fuel pump
• Fuel filter
• Fuel pressure regulator
• Injectors

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Fuel Delivery System
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Electric Fuel Pump

• Draws gasoline out of the tank
• Forces it to the fuel rail
• Unused fuel returns to the tank

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Fuel Pressure Regulator

• Controls pressure entering injector(s)
• Returns excess fuel to the tank
• Vacuum may be ported into the regulator
• lower pressure at idle
• increasing pressure at higher load

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Fuel Pressure Regulator
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Injectors

• Solenoid-operated fuel valve
• When current flows, magnetism attracts armature
  to open injector

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Air Induction System

• Air filter
• traps dust and debris
• Throttle valve(s)
• controls airflow through throttle body
• Sensors
• sense airflow and throttle position
• Ducts
• route clean air to throttle body

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Air Induction System

• Throttle plates control airflow

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Sensor System

• Inputs to the control module
• Signal the following operating conditions
• temperature
• position
• pressure or vacuum
• speed

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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

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Engine Sensors

• Exhaust gas oxygen
• Manifold absolute pressure (MAP)
• Throttle position (TP)
• Engine coolant temperature(ECT)
• Airflow
• Inlet air temperature (IAT)
• Crankshaft position (CKP)

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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

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Oxygen Sensor

• Signals air-fuel mixture

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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

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Oxygen Sensor Construction
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Open Loop

• Injection system does not use exhaust gas oxygen
  as an indicator of air-fuel mixture
• Operation is from information stored in the
  computer
• Cold engines operate in open loop

Closed Loop

• Computer uses exhaust oxygen as a main input for
  air-fuel mixture control
• Normally, hot engines operate in closed loop

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Information Flow
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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

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Map Sensor

• Often mounted on the engine or in the engine
  compartment

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MAP Sensor Theory

• Piezo-resistor chip converts pressure change into
  resistance change

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MAP Sensor Side View

• Manifold vacuum flexes the chip, altering its
  resistance

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Throttle Position Sensor

• Senses throttle position
• Variable resistor connected to the throttle plate
• As the throttle opens, sensor resistance changes,
  signaling throttle position

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Throttle Position Sensor

• Variable resistor signals throttle position

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Engine Coolant Temperature Sensor

• Senses engine coolant temperature
• At 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

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Airflow Sensor

• Measures amount of air entering engine
• Air flap or door operates a variable resistor
• Airflow opens the flap, changing position of the
  variable resistor, changing the signal voltage to
  the computer

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Airflow Sensor Operation

• Airflow sensor operates a variable resistor

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Inlet Air Temperature Sensor

• Measures temperature of air entering the engine
• Air temperature affects air density
• Cooler air is more dense, requiring more fuel
• Operation is similar to engine coolant
  temperature sensor

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Crankshaft Position Sensor

• Detects engine speed and position
• Information is used by computer for ignition
  timing and fuel injection operation

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Other Sensors

• Several other sensors may be used
• A/C compressor sensor
• transmission sensor
• EGR sensor
• vehicle speed sensor
• knock sensor

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Digital Signals

• Signal is on or off
• Voltage goes from maximum to minimum instantly,
  like a switch
• Crankshaft position sensor output may be a
  digital signal

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Analog Signals

• Signal varies in voltage or strength
• May be produced by change in resistance of a
  sensor, sensing changes in temperature, pressure,
  or position

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Injector Pulse Width

• 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

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Injector Pulse Width

• Pulse width controls the amount offuel injected

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Throttle Body Injection

• Components
• throttle body housing
• TBI injector
• TBI pressure regulator
• idle speed control
• throttle position sensor
• throttle plates

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TBI Overview
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TBI Assembly

• Fuel enters the regulator before passing into the
  injector

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Throttle Body Housing

• Bolted to the intake manifold
• Injector(s) are in the upper housing
• Throttle plates are in the lower housing
• Holds the throttle position sensor, fuel pressure
  regulator and idle speed control device

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TBI Injector

• Components
• solenoid coil
• armature or plunger
• ball or needle valve
• seat

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TBI Injector

• This injector uses a ball-type valve instead of a
  pointed needle valve

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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

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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

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TBI System Cutaway
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Engine Idle Speed Control

• There are several different types of idle speed
  control devices
• fast idle thermo valve
• idle air control motor
• throttle positioner

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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

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Fast Idle Thermo Valve

• Idle air control valve and the thermo valve
  affect air that bypasses the throttle valve to
  alter idle speed

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Idle Air Control Motor

• Computer controlled solenoid or
  servomotor-operated air bypass valve

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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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Continuous ThrottleBody Injection (CTBI)

• 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

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Electronic Multiport Injection

• Uses a computer, sensors and one solenoid
  injector for each cylinder
• Components
• multiport throttle body
• multiport pressure regulator
• fuel rail

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Multiport Fuel Injection
Controls
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Multiport Fuel Injection
Air Delivery
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Multiport Fuel Injection
Fuel Delivery
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Injection Components

• Throttle body
• contains throttle plates and a throttle position
  sensor
• Multiport pressure regulator
• mounted on the fuel rail, maintains pressure at
  the inlet to the injectors by acting as a bypass

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Injection Components

• Fuel rail
• connects the main fuel line to the inlet of each
  injector
• Multiport fuel Injector
• sprays fuel into the intake port, below the
  throttle valve

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Injection Components
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Injection Components
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Multiport Fuel Injector

• Solenoid opens the injector when current flows
  through the coil

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Air-Fuel Emulsion Injector

• Mixes air with the fuel creating a slurry
• Slurry is injected into the intake manifold
• Atomizes the fuel and improves combustion
• Low pressure air from the air injection pump may
  be used

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Air-Fuel Emulsion Injector
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Unitized Multiport Injection

• 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

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Components

• 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

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Components

• 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

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Unitized Injector

• Note the fitting for the plastic transfer line

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Injector Resistor Pack

• Set of low-ohm resistors
• Control current flow to each injector coil
• Protect windings from excess current
• Usually 5-7 ohms
• Often mounted in the engine compartment

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Injector Circuit
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Airflow Sensing Multiport EFI

• 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 moved open for more power, increased
flow pushes sensor flap open
Throttle almost closed, sensor detects little
airflow
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Pressure-Sensing Multiport EFI

• 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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Hydraulic-Mechanical Continuous Injection System
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Continuous Injection System (CSI)

• Hydraulic-mechanical system
• Mixture control unit senses airflow with an
  airflow sensor plate and distributes fuel
• Operates the injectors with a fuel distributor

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Continuous Injection System (CSI)
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Airflow Sensor

• Disc-shaped plate, hinged in the air horn
• Plate operates a lever arm
• Lever 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 mechanism
• Controls fuel flow or pressure to each injector
• Whenever air flows to the engine, the fuel
  distributor sends fuel to the injectors, causing
  them to spray continuously

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CIS Operation
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Continuous Fuel Injector

• Spring-loaded valve
• One injector for each cylinder
• Injects fuel continuously when the engine is
  running
• Spring holds the valve closed
• Fuel pressure forces it open, spraying fuel into
  the intake port
• Spring-loaded valve
• Fuel pressure forces the valve open

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Continuous Fuel Injector
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Cold Start Injector

• Extra fuel injector
• Sprays fuel into the intake plenum for cold
  engine starting and running
• Improves cold operation by enriching the air-fuel
  mixture
• Controlled by a thermo-time switch or control
  module

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Cold Start Injector
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Fuel Accumulator

• Damps pressure pulses
• May 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