toyota training course t874 engine control systems II ch06

Section 6

Ignition Systems

Slide 69

Ignition Systems The purpose of the ignition system is to ignite the air/fuel mixture in the
combustion chamber at the proper time. The ECM gathers information
from a variety of sensors and its internal programming to determine when
to command the ignition system to produce a spark in a specific cylinder
and ignite the air/fuel mixture.

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Course 852

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Typical Components

Ignition Systems

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Slide70
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T874f509, T874f310, T852f129
T874f508

Typical Components

Regardless of type, essential ignition system components include:

•Crankshaft position sensor (NE signal): Determines crankshaft
position for spark timing.

•Camshaft position sensor (also called VVT sensor) (G signal):
Determines when cylinder #1 is at top dead center (TDC) on the
compression stroke for spark timing.

•Igniter: When commanded by the ECM, controls current through
the coil primary winding.
•Ignition coils: Current through the coil windings creates the high
voltage required to produce a spark at the spark plugs.

•Spark plugs: High voltage jumps the air gap, creating a spark that
ignites the air/fuel mixture.
•ECM and input sensors: Control the timing of spark generation.
•Wiring harness: Carries signals throughout the system.

All ignition system components are manufactured to match in function
and construction. If parts from different systems are combined, the
components or engine may be damaged. Always use the correct parts
specified for the vehicle.

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Ignition Systems

IGT and IGF Signals

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Slide71
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T874f509, T874f310, T852f133
T874f508

Ignition Control Signals:
IGT

The primary coil current is controlled by the ECM through the Ignition
Timing (IGT) signal. The IGT signal is a voltage signal that turns ON/
OFF the main transistor in the igniter to start/stop primary coil current.
When IGT signal voltage drops to 0 volts, the transistor in the igniter
turns OFF, stopping current in the primary coil. When the current in the
primary coil is turned OFF, the rapidly collapsing magnetic field induces
a high voltage in the secondary coil. If the voltage is high enough to
overcome the resistance in the secondary circuit, there will be a spark at
the spark plug.

Ignition Control Signals:
IGF

The Ignition Confirmation (IGF) signal is used by the ECM to determine
if the ignition system is working. As the ECM cuts the current to the
primary coil ON and OFF, the igniter sends back an IGF signal to the
ECM to confirm proper operation. There are different fail-safe modes
depending on the type of ignition system, cylinder displacement, and

model year.
On most engines with one ignition coil/igniter per cylinder, the ECM
will turn off one cylinder’s fuel injector if there is no IGF signal for that
cylinder and if engine conditions (such as load and temperature) could
lead to catalytic converter damage. Even if the IGF signal returns to
normal while the engine is running, the injector may remain off until the
next engine start. This will set a DTC.

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Course 852

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Ignition Advance and Firing Order

Ignition Systems

Slide 72
T852f127/T852f128

Ignition Advance

Ignition must occur earlier when the engine speed is high and later when
it is low. Ignition must also be advanced when manifold pressure is low.
Optimal ignition timing is also affected by a number of other factors
besides engine speed and intake air volume, including fixed factors such
as the shape of the combustion chamber and variable factors such as the
temperature inside the combustion chamber.

In order to maximize engine output efficiency, the air/fuel mixture must
be ignited so that maximum combustion pressure occurs at about 10°
after-top-dead-center (ATDC).
Early systems relied on mechanical and vacuum-controlled advance
mechanisms in the distributor. Now, spark timing and distribution is
completely controlled by the ECM and direct ignition system.

Firing Order

The firing order is also controlled by ECM programming. Firing order for
a specific engine can be found in TIS.
Cylinder numbering varies by engine design, usually with the number 1
cylinder farthest forward:

•V8 engine cylinders are arranged with odd-numbered cylinders on
the left bank and even numbered cylinders on the right bank.

•V6 engine cylinders are arranged with even-numbered cylinders on
the left bank and odd-numbered cylinders on the right bank.
•In-line 4- and 6-cylinder engines are arranged consecutively 1–4 or
1–6.

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Spark Plug Types

Ignition Systems

Slide
Slide73
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T874f509, T874f310, T874f508
285EG40

Spark Plug Types

It is important to use the correct specification and design spark plug for
each engine. The wrong plugs can affect driveability, emissions, and
engine durability. Current plug designs include:

•Conventional spark plugs are used on certain models. They have a
service interval of 30,000 miles.
•Double platinum spark plugs are available for certain models.
Platinum on both the center and ground electrodes reduces wear
while providing a service life of up to 60,000 miles. The raised
electrode design provides excellent ignitability for a strong spark,
translating into a smooth idle and strong performance. Nickel
and iridium are added to the platinum for strength and durability
(resistance to cracking).

•Iridium spark plugs are used on certain models. Iridium provides
greater durability than platinum and allows for a 120,000-mile
maintenance interval.

•Long-reach spark plugs are used on many late model vehicles. The
long-reach design allows the area of the cylinder head where the
plug is mounted to be thick. The water jacket can be extended near

the combustion chamber, which contributes to cooling performance.
Service mileage intervals can be found in the Owner’s Manual in TIS.

Toyota Engine Control Systems I

Course 852

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Spark Generation and Electronic Spark Advance

Ignition Systems

Slide
Slide74
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T874f509, T874f310, T852f130
T874f508

Spark Generation The ignition coil must generate a high voltage to produce a spark to ignite the
air/fuel mixture. A strong magnetic field is used to produce this power. The
magnetic field is created by current in the primary coil winding. The primary
coil winding has a very low resistance, allowing maximum current. The more
current, the stronger the magnetic field. The power transistor in the igniter
handles the high current needed by the primary coil.
Another requirement to produce high voltage is that current in the primary coil
winding must be turned OFF quickly. When the transistor in the igniter turns
OFF, current stops and the magnetic field collapses. As the rapidly collapsing
magnetic field passes through the secondary winding, voltage (electrical

pressure) is created. If enough voltage is created to overcome the resistance in
the secondary circuit (mostly at the spark plug gap), there will be current and a
spark in the combustion chamber.
Note that the higher the resistance in the secondary circuit, the more voltage
will be required to begin current and the ignition spark duration will be shorter.
Electronic Spark Advance
(ESA)

The Electronic Spark Advance (ESA) system provides optimum ignition
timing characteristics for the best combination of low emissions, fuel
efficiency, and engine power output.
The ECM determines ignition timing based on sensor inputs and on its internal
memory, which contains the optimal ignition timing data for each engine
running condition.
•After determining the ignition timing, the ECM sends the ignition
timing signal (IGT) to the igniter.

•When it receives the IGT signal, the igniter shuts off current in the
primary ignition coil, producing a high voltage spark in the cylinder.
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Ignition Systems

Direct Ignition System (DIS)

Slide 75
T852f171/151EG05/281EG40

Direct Ignition The Direct Ignition System (DIS) improves ignition timing accuracy,
System (DIS) reduces high-voltage loss, and enhances the overall reliability of the
ignition system by eliminating the distributor.
DIS has an ignition coil mounted on each spark plug. Some older DIS
designs had one igniter for all cylinders, while modern DIS is classified
as independent, meaning it has one igniter per cylinder.

Toyota Engine Control Systems I

Course 852

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DIS Diagnostics

Ignition Systems

Slide 76

DIS Diagnostics

DIS has eliminated many previous ignition system services and
adjustments. For example:

•Because the G and NE signal sensors are fixed in position, ignition
timing cannot be adjusted.
•When the igniter is built into the ignition coil, it is not possible to
do a resistance check of the primary coil winding. A bad primary

winding will have to be determined by checking other functions of
the coil and the ignition circuit.

The first step in DIS diagnosis should always be to connect the
Techstream and observe the Data List with the engine running under
various conditions.
Other initial diagnostics include:
•Swapping igniters

•Checking for spark with a spark tester

•Checking +B at the coil while cranking
•Checking IGF signal at the ECM
•Checking ground

Refer to the Repair Manual for specific system operating parameters and
test specifications.

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