Section 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 Toyota Engine Control Systems I Course 852 61 Typical Components Ignition Systems Slide Slide70 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 62 TOYOTA Technical Training Ignition Systems IGT and IGF Signals Slide Slide71 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 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 Toyota Engine Control Systems I Course 852 63 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 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 64 TOYOTA Technical Training Spark Plug Types Ignition Systems Slide Slide73 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 65 Spark Generation and Electronic Spark Advance Ignition Systems Slide Slide74 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 66 TOYOTA Technical Training 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 67 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 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 68 TOYOTA Technical Training ... Owner’s Manual in TIS Toyota Engine Control Systems I Course 852 65 Spark Generation and Electronic Spark Advance Ignition Systems Slide Slide74 T874f509, T874f310, T852f130 T874f508 Spark Generation... the engine is running, the injector may remain off until the next engine start This will set a DTC Toyota Engine Control Systems I Course 852 63 Ignition Advance and Firing Order Ignition Systems. .. engines are arranged consecutively 1–4 or 1–6 64 TOYOTA Technical Training Spark Plug Types Ignition Systems Slide Slide73 T874f509, T874f310, T874f508 285EG40 Spark Plug Types It is important