Service manual - TOYOTA Technical Training-Introduction to Engine Control Systems(Lessons)[2005-ENG].pdf

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Section 1
Introduction to Engine Control Systems
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Lesson Objectives 1. Identify major control systems/components
2. Locate needed engine control systems service information
3. Familiar with engine control systems terms
Engine Control Systems I - Course 852
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Section 1
TOYOTA Technical Training
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Section 1
Introduction to Engine Control Systems
Basic Engine
Operation
The need to achieve high power output, high fuel economy, and the
lowest amount of emission gases from today’s engines has led to very
sophisticated engine control systems. A computer, referred to as an
Engine Control Module (ECM), manages a variety of engine systems.
These systems are basically divided into the following areas:
• Air induction systems.
• Fuel system.
• Ignition system.
• Exhaust/Emission control system.
All the above and other systems are controlled or sensed by the ECM.
The ECM with its sensors and actuators is often referred to as the
electronic control system. It is important to keep in mind while
diagnosing engine concerns that the fundamentals of engine operation
(correct mixture of air and fuel sufficiently compressed and ignited at
the proper time) are not different. The following is an overview of these
systems.
Basic Air
Induction System
Air Cleaner
The amount of air is
measured and the air is
controlled for efficient
engine operation. The
idle air control valve is
not used on electronic
throttle controlled
systems. On some
engines, an intake
manifold pressure sensor
is used in place of an air
flow sensor.
Air Flow Sensor
Throttle Body
Idle Air Control Valve
Air Intake Chamber
Intake Manifold
Intake Manifold
Pressure Sensor
Cylinders
Fig. 1-01
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Engine Control Systems I - Course 852
1-1
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Section 1
Air Induction
System
Air filtered by the air cleaner is measured by the air flow sensor
(commonly called the mass air flow sensor). The volume of air is
regulated by the throttle valve. The idle air control valve regulates the
amount of air bypassing the throttle valve to adjust idle speed. The air
intake chamber and intake manifold are tuned for efficient engine
operation.
There are many variations on the basic air induction system. The
Acoustic Controlled Induction System (ACIS) modifies air intake runner
length for greater efficiency. Some engines have turbochargers or
superchargers to provide additional air.
Basic Fuel
Injection System
Based on signals
received, the ECM
calculates how long and
when to turn on the
injectors to deliver the
correct amount of fuel.
*The location of the
pressure regulator varies
with system. When
excess fuel is returned to
the fuel tank (return
type) the pressure
regulator is after the
injectors. On the
returnless fuel system,
the pressure regulator is
in the fuel tank.
Fig. 1-02
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Fuel System
The fuel system needs to deliver the correct volume of fuel to the
cylinders under a variety of conditions.
Fuel is pressurized by the fuel pump and flows to the fuel injectors. A
pressure regulator, located in the fuel tank or after the injectors,
regulates fuel pressure. The ECM controls when and how long the fuel
injectors are on. The injectors, when on, allow fuel to flow into the
intake manifold. The ECM calculates how much fuel to be injected
based on a variety of parameters, primarily temperature and intake air
volume.
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TOYOTA Technical Training
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Engine Control Systems
There are other components used on a fuel injection system to modify its
operation and are covered in the fuel system section.
Basic Ignition System
Fig. 1-03
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Ignition Systems
Based on engine operating conditions, the ECM determines when to ignite
the air/fuel mixture according to its programming. The igniter turns the
ignition coil(s) on and off based on a signal from the ECM. The high
voltage needed to create the spark is generated in the coil(s).
Exhaust and Emission Systems
Fig. 1-04
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Engine Control Systems I - Course 852
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