1997+ Mercury 35/40HP 2 Cylinder Outboards Service Manual PN 90-826148R2, Page 60Get this manual
Theory of Operation The ignition system is alternator-driven with distributor-less capacitor dischargeMajor components of the ignition system are the flywheel, stator, trigger, timing protection module (TPM), capacitor discharge modules (CDM) and spark plugsThe stator assembly is mounted stationary below the flywheel and has (red stator has 3) capacitor charging coils wound in seriesThe flywheel is fitted with permanent magnets inside the outer rimAs the flywheel rotates the permanent magnets pass the capacitor charging coils causing the coils to produce AC voltage (230330 volts)The AC voltage then is conducted to the capacitor discharge module (CDM) where it is rectified and stored in capacitorPart of the stator voltage (2025 volts) is sent to the timing protection module (TPM) to power the timing circuitThe trigger assembly (also mounted under the flywheel) has coilThe flywheel has another permanent magnet located around the center hubAs the flywheel rotates, this hub magnet passes the trigger coilThis causes the trigger coil to produce AC voltage pulse which is sent to the TPMThe TPM delays this signal depending on engine RPM and forwards trigger signal to electronic switch (SCR) within the CDMThe SCR switch discharges the stored voltage of the capacitor into the primary side of the CDM's ignition coilCapacitor voltage within the CDM is amplified as high as 45000 volts to jump the gap at the spark plugThe preceding sequence occurs once-per-enginerevolution for each cylinderSpark timing is changed (advancedretarded) electronically by the TPM monitoring trigger pulsesIMPORTANT: If the engine misfires, runs rough or does not start, the ignition system should be checked using Multi-MeterDVA Tester (91-99750), or voltmeter (capable of measuring 400 volts DC, or higher) and Direct Voltage Adaptor (91-89045)