Ignition Circuitry


The engine ECU determines the ignition timing based on the G signal, NE signal and the signals from other various sensors. When the ignition timing has been determined, the engine ECU sends the IGT signal to the igniter. While the IGT signal sent to the igniter is ON, the primary current flows to the ignition coil. While the IGT signal turns OFF, the primary current to the ignition coil is shut off. At the same time, the IGF signal is sent to the engine ECU. Currently, the main ignition circuitry used is the DIS (Direct Ignition System). The engine ECU distributes the highvoltage current to the cylinders by sending each IGT signal to the igniters in the order of ignition. This makes it possible to provide highly accurate ignition timing control.
Distributor Type Ignition Circuitry
The distributor type ignition circuitry is a system that uses a distributor to send high-voltage current to the spark plugs. The distributor type ignition circuitry conducts basically the same control as the DIS. However, because there is only a single igniter and ignition coil, only one IGT and IGF are output. The high voltage generated by the ignition coil is distributed to each cylinder by the distributor.
IGT and IGF Signal
1. IGT signal
The engine ECU calculates the optimum ignition timing according to the signals from various sensors and sends the IGT signal to the igniter. The IGT signal is turned ON immediately before the ignition timing calculated by the microprocessor in the engine ECU, and then is turned OFF. When the IGT signal is turned OFF, the spark plug sparks.
2. IGF signal
The igniter sends an IGF signal to the engine ECU by using the counter-electromotive force that is generated when the primary current to the ignition coil is shut off or by using the primary current volume. When the engine ECU receives the IGF signal, it determines that ignition occurred. (This does not mean, however, that there was actually a spark.) If the engine ECU does not receive an IGF signal, the diagnosis function operates and a DTC is stored in the engine ECU and the fail-safe function operates and stops injecting fuel.

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