toyota training course t874 engine control systems II ch06

Slide 1 T874f509, T874f310, T874f508 Regardless of type, essential ignition system components include: • Crankshaft position sensor NE signal: Determines crankshaft position for spark t

Ignition Systems

Slide 69

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

Ignition Systems

Section 6

Slide 1 T874f509, T874f310, T874f508

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

Typical Components

Slide 70 T852f129

Slide 1 T874f509, T874f310, T874f508

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

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

Ignition Control Signals:

IGT

Ignition Control Signals:

IGF

Slide 71 T852f133

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

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

Ignition Advance

Ignition Advance and Firing Order Ignition Systems

Firing Order

Slide 72 T852f127/T852f128

Slide 1 T874f509, T874f310, T874f508

Slide 73 285EG40

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

Spark Plug Types

Slide 1 T874f509, T874f310, T874f508

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 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

Spark Generation

Electronic Spark Advance

(ESA)

Slide 74 T852f130

Spark Generation and Electronic Spark Advance Ignition Systems

The Direct Ignition System (DIS) improves ignition timing accuracy, 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

Direct Ignition

System (DIS)

Slide 75 T852f171/151EG05/281EG40

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

DIS Diagnostics

Slide 76