Service manual

90-898303 2-29

Theory of Operation

The V– 6 Outboard CDM ignition system is alternator– driven with distributor–

less capacitor discharge. Major components of the system are the flywheel,

stator assembly, trigger assembly, control module, 6 CDM assemblies and 6

spark plugs.

The stator assembly is mounted below the flywheel and has 3 capacitor

charging coils. The flywheel is fitted with permanent magnets inside the outer

rim. As the flywheel rotates, the permanent magnets pass the capacitor

charging coils producing AC voltage. The AC voltage is conducted to the

CDMs where it is rectified, regulated to 300 volts, and stored in capacitors.

The trigger assembly (also mounted under the flywheel) has 3 coils. Each coil

controls the spark to 2 cylinders - one on each bank. The flywheel also has a

second set of permanent magnets located around the center hub. As the

flywheel rotates, the magnets pass the trigger coils producing AC voltage. The

AC voltage is conducted to the control module, which shapes the signal before

sending it to the electronic switch (SCR) inside the appropriate CDM. The

switch discharges the capacitor voltage into the primary side of the ignition coil

(inside the CDM).

As this voltage goes to ground through the primary circuit of the coil, it induces

a voltage rise in the secondary side of the ignition coil. This voltage can

increase to approximately 40,000 volts before bridging the spark plug gap and

returning to ground.

The preceding sequence occurs once per engine revolution for each cylinder.

Spark timing is advanced or retarded by the movement of the trigger assembly

attached to the throttle/spark arm.

The control module provides rev– limit (carb models), bias control, shift

stabilizer, idle stabilizer, injector timing signal (EFI models), and low oil

warning.

Capacitor Charging #1, #2, & #3 CDMs

The STATOR assembly is mounted to the block below the flywheel and has 3

CAPACITOR CHARGING COILS connected in series. The FLYWHEEL is

fitted with 6 permanent magnets inside the outer rim. The flywheel rotates the

permanent magnets past the capacitor charging coils causing the coils to

produce AC voltage (260-320 volts). The AC voltage is then conducted to the

CAPACITOR DISCHARGE MODULES (CDM), where it is rectified (DC) and

stored in a capacitor. The stator voltage return path is through the ground wire

one of the other CDMs and back through that CDM’s charging coil wire to the

capacitor charging coils.

NOTE: The CDM contains a zener diode (not shown for clarity). The zener

diode regulates the capacitor voltage to 300 volts, preventing overcharging of

the capacitor (and possible failure) if the SCR does not receive a trigger pulse.

Notes

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