Ignition System Control

- The ECM determines operating condition of the engine based on signals from the pressure sensor, engine coolant temperature sensor, intake air temperature sensor, crankshaft position sensor and other sources. It then selects the ignition timing most appropriate for the condition thus determined from those stored in its memory and outputs at that timing a primary current OFF signal to the ignitor to initiate ignition.
- This control uses a quick-to-response learning feature by which the data stored in the ECM memory is processed in comparison with information from various sensors and switches.
- Thus, the ECM can always perform optimum ignition timing taking into account the output, fuel consumption, exhaust gas, and other factors for every engine operating condition.




- Ignition control during start-up
Engine speed fluctuates during start of the engine, so the ECM cannot control the ignition timing. During that period, the ignition timing is fixed at 10° BTDC by using the 10° signal from the crankshaft position sensor.

- The ECM receives two types of crank angle signal pulse; one is generated every 10° of crankshaft rotation and the other, every 30° of crankshaft rotation. Using these two types of signal pulse, the ECM determines the position of each piston as follows:
The ECM interprets the pulses of range (A) shown below as the No.1 and No.2 cylinder pistons being at TDC, the pulses of range (B) as the No.5 and No.6 cylinder pistons being at TDC, and the pulses of range (C) as the No.3 and No.4 cylinder pistons being at TDC.




- The ECM outputs an ignition signal for the No.1, No.3 or No.5 cylinder when it receives a camshaft angle pulse before a TDC signal and for the No.2, No.4 or No.6 cylinder when it receives no camshaft angle pulse before a TDC signal.