Service manual

90-898303

3-11

Theory of Operation

Ignition current is generated by the stator under the flywheel. The stator

consists of six bobbins - one for each cylinder. The positive current wave

charges the capacitor in the capacitor discharge module (CDM). The

electronic control module (ECM) activates the switching device (SCR) in the

CDM which allows the capacitor to discharge, causing the spark to occur.

Ignition timing is regulated by the ECM which receives status input from a

variety of sensors. These sensors include: crank position, throttle position

sensor (TPS), engine temperature. There are six CDMs - one for each

cylinder. The CDM consists of a capacitor, switching device, primary winding,

secondary winding, and spark plug lead.

Ignition Component Description

ELECTRONIC CONTROL MODULE (ECM)

a) Electronic Control Unit

Under normal conditions, ECM controls and provides:

Spark timing

by monitoring engine RPM, throttle shutter opening and coolant

temperature.

Cold engine starting

by advancing spark timing.

Over-speed protection

in the event engine RPM exceeds 6000 for carb

models and 6100 for EFI models. This is accomplished in two stages. Initially

timing is gradually retarded to reduce RPM to 5900 for carb models and 6000

for EFI models. If RPM continues to increase above 6400 for carb models and

6500 for EFI models – i.e.– propeller breaks water surface – timing will rapidly

retard to 2° ATDC to prevent any further RPM increase. When an over speed

condition occurs, the low-oil and overheat lamps will illuminate alternately and

the warning horn will be activated.

Notes

_______________________