Smart Ignition Modules
Smart Ignition modules like Bosch BIM137 or 139 should not be used.
Falling Egde & Rising Edge on Ignition Modules
The Waveform that the ignition module expects can vary depending on which edge the
module fires a spark.
• Falling edge triggered – Most factory ignition modules are falling edge triggered.
These modules expect a 0 Volt input signal when the ignition system is idle. When
the voltage goes to 12V, the coil is being charged, when the input returns to 0 V, a
spark is fired and the coil then sits idle until the input voltage to the ignition module
is again raised to 12 Volt.
Falling spark edge, 70/30 Duty cycle for smart ignition module and Autronic CDI.
• Rising edge triggered – Some ignition modules like Honda and MSD CDI are
known to be rising edge triggered. These modules expect a 12 Volt input signal
when idle. When the voltage falls to 0 Volt, the module charges the coil. When
voltage returns to 12 volt, the spark is fired.
Rising spark edge
The Coil Negative Signal
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