Outline
The igniter carries out the precise interruption of the primary current that flows to the ignition coil in accordance with the ignition signal (IGT) that is output by the engine ECU.
IGT signal
When the IGT signal turns from off to on, the igniter starts the flow of the primary current.
Constant current control
When the primary current reaches a specified value, the igniter limits the maximum amperage by regulating the current.
Dwell angle control
To ensure the proper duration of the primary current, which decreases as the engine speed rises, this control regulates the length of time (dwell angle) during which current flows. (On some of the recent models, this control is effected through the IGT signal.) When the IGT signal turns from on to off, the igniter shuts off the primary current. At the instant the primary current is shut off, hundreds of volts are generated in the primary coil and tens of thousands of volts are generated in the secondary coil, which cause the spark plug to spark.
IGF signal
The igniter carries out the precise interruption of the primary current in the ignition coil in accordance with the IGT signal of the engine ECU. Then, the igniter transmits an ignition confirmation signal (IGF) to the engine ECU in accordance with the amperage of the primary current. The IGF is output when the primary current that flows from the igniter reaches the prescribed value IF1. When the primary current exceeds the prescribed value IF2, the system determines that the required amount of current has flowed, and allows the IGF signal to return to its original voltage. (The waveforms of the IGF signal vary from model to model.) If the engine ECU does not receive an IGF signal, it determines that a failure has occurred in the ignition system. To prevent the catalyst from overheating, the engine ECU stops the fuel injection and stores the failure in the diagnosis function. However, the engine ECU will be unable to detect a failure in the secondary current circuit because the engine ECU monitors only the primary current circuit for an IGF signal.
HINT:
On some models, an IGF signal is determined through the primary voltage.