Ignition System
The ECU’s interface to the ignition system is trough the ignition module or a CDI. There
are two types of ignition modules available in common use on factory ignition systems.
The following can cause fault in the ignition modules
• Over heating
• Incorrect coil charge time
• Incorrect output type (Pulse or Dwell)
• Incorrect output edge
• Poor power or ground circuits
The ignition module ground is vital to the operation of the module. If the ground is not in
good condition, it can cause a reduction in primary current which affects current limiting
or dwell control. Do not ground igniter at same point as SM4.
Dumb Ignition Modules
The Dumb ignition module requires the SM4 to perform the dwell control or charge time
of the ignition coil. The signal from SM4 determines the charge time of the coil and tries
to maintain the specified charge time from the Ignition Dwell table at all engine speeds.
Example of dumb ignitions modules:-
Single type Bosch 0 227 100 124
Triple type Bosch 0 227 100 203 and 0 227 100 209.
Quad type Bosch 0 227 100 211
Typically charge time is 2.5 ms for normal coils and 1.8 ms for small coil on plug.
See chapter Dwell for more information regarding how to fin out coil charge time.
For a dumb ignition module with falling spark edge, with 4ms coil charge time, the SM4
ignition output will look like the following waveform:
Warning:
Never use Pulse on Dwell Control Mode when using a Dumb Ignition module. Using
constant cycle (pulse) signal on a dumb ignition module may cause the ignition coils
to be damaged from overcharging. Ignition module may also be damaged as a
consequence.
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