Transcript Ch 22 GAS INJECTION FUNDAMENTALS

by
Russell Krick
Publisher
The Goodheart-Willcox Co., Inc.
Tinley Park, Illinois
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(18 Topics)
Gasoline injection fundamentals
Gasoline injection classifications
Throttle body and multiport injection
Gasoline injection controls
Electronic fuel injection
Engine sensors
Injector pulse width
Throttle body injection
Engine idle speed control
Continuous throttle body injection
Electronic multiport injection
Air-fuel emulsion injector
Unitized multiport injection
Injector resistor pack
Airflow sensing multiport EFI
Pressure sensing multiport EFI
Hydraulic-mechanical continuous
injection system
Fuel accumulator
Uses pressure from an electric fuel
pump to spray fuel into the engine’s
intake manifold
Provides the engine with the correct airfuel 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
Closed throttle,
high vacuum
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Open throttle,
reduced vacuum
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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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
Injection
Injector nozzles in
a throttle body
assembly on top of
the engine
Multiport
Injection
Gasoline is
sprayed into each
intake port, toward
each intake valve
Indirect Injection
Sprays fuel into intake
manifold. Most gasoline
systems are indirect
Direct Injection
Sprays fuel directly into
engine combustion
chambers. Used in all
diesel injection systems
Electronic fuel injection
Hydraulic fuel injection
Mechanical fuel injection
Injection timing
Injector opening relationship
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)
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
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
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
Injector Opening
Relationship
Group Injection
Several, but not all injectors open at the
same time
V-8 engine–one group of injectors open at
one time, another group of four open at a
different time
Electronic Fuel
Injection (EFI)
EFI system can be divided into four
subsystems:
fuel delivery system
air induction system
sensor system
computer control system
Systems Overview
Fuel Delivery System
Components
Electric fuel pump
Fuel filter
Fuel pressure regulator
Injectors
Fuel Delivery System
Electric Fuel Pump
Draws gasoline out of the tank
Forces it to the fuel rail
Unused fuel returns to the tank
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
Fuel Pressure
Regulator
Low vacuum,
high load
High vacuum,
low load
Injectors
Electrical
terminals
Solenoid-operated
fuel valve
When current
flows, magnetism
attracts armature
to open injector
Fuel
inlet
Inlet
screen
Return
spring
Armature
Injector
body
Needle
valve
Coil
windings
Spray
mist
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
Air Induction System
Throttle plates control airflow
Sensor System
Inputs to the control module
Signal the following operating
conditions:
temperature
position
pressure or vacuum
speed
Computer Control
System
Uses data from
the sensors to
control fuel
injectors
Wiring harness
connects
computer to
sensors and
injectors
Electronic Control
Module
Commonly
mounted behind
the instrument
panel
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Exhaust gas oxygen
Manifold absolute pressure (MAP)
Throttle position (TP)
Engine coolant temperature(ECT)
Airflow
Inlet 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 Sensor
Signals 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 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
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 Sensor
Often mounted on the engine or in the
engine compartment
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
Throttle Position
Sensor
Variable resistor signals throttle position
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
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
Airflow Sensor
Operation
Airflow sensor operates a variable resistor
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
Crankshaft Position
Sensor
Detects engine speed and position
Information is used by computer for
ignition timing and fuel injection
operation
Other Sensors
Several other sensors may be used:
A/C compressor sensor
transmission sensor
EGR sensor
vehicle speed sensor
knock sensor
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
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
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
Injector Pulse Width
Pulse width controls
the amount of
fuel injected
Components:
throttle body housing
TBI injector
TBI pressure regulator
idle speed control
throttle position sensor
throttle plates
TBI Overview
TBI Assembly
Fuel enters the
regulator before
passing into the
injector
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
TBI Injector
Components:
solenoid coil
armature or plunger
ball or needle valve
seat
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 valve
idle air control motor
throttle 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
Fast Idle Thermo Valve
Idle air control
valve and the
thermo valve affect
air that bypasses
the throttle valve to
alter idle speed
Idle Air Control Motor
Computer 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
Continuous Throttle
Body 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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Uses a computer, sensors and one
solenoid injector for each cylinder
Components:
multiport throttle body
multiport pressure regulator
fuel rail
Multiport Fuel Injection
Controls
Multiport Fuel Injection
Air Delivery
Multiport Fuel Injection
Fuel Delivery
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
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
Injection Components
Multiport Fuel Injector
Solenoid opens the
injector when
current flows
through the coil
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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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
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
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
Unitized Injector
Note the fitting
for the plastic
transfer line
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
Circuit contains
resistor pack
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Each pin corresponds
to a resistor
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
Throttle almost
more power, increased flow
closed, sensor
pushes sensor flap open
detects little airflow
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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 system
Mixture control unit senses airflow with
an airflow sensor plate and distributes
fuel
Operates the injectors with a fuel
distributor
Continuous Injection
System (CSI)
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
Airflow sensor
Partial load, more airflow
Idle, low airflow
Full load, airflow pushes
plate up high
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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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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
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