Installation manual

1-65

90-898305

Electrical

The electrical system consists of the PCM, crank position sensor (flywheel

speed & crankshaft position), throttle position sensor (TPS), MAP sensor,

engine temperature sensor, ignition coils and injectors (fuel & direct). The

engine requires a battery to start (i.e. the ignition and injection will not occur if

the battery is dead). The system will run off of the alternator.

Operation

The operation of the system happens in milliseconds (ms). Exact timing is

critical for engine performance. As the crankshaft rotates, air is drawn into the

crankcase through the throttle shutter, into the plenum and through the reed

valves. As the piston nears bottom dead center, air from the crankcase is

forced through the transfer system into the cylinder. As the crankshaft

continues to rotate the exhaust and intake ports close. With these ports

closed, fuel can be injected into the cylinder. The PCM will receive a signal

from the throttle position sensor (TPS), engine temperature sensor (TS) and

the crank position sensor (flywheel speed and position sensor). With this

information, the PCM refers to the fuel calibration (maps) to determine when

to activate (open and close) the injectors and fire the ignition coils. With the

piston in the correct position, the PCM opens the fuel injector, 744.6 kPa (108

psi) fuel is discharged into a machined cavity inside the air chamber of the

air/fuel rail. This mixes the fuel with the air charge. Next the direct injector will

open, discharging the air/fuel mixture into the combustion chamber. The direct

injector directs the mixture at the bowl located in top of the piston. The piston’s

bowl directs the air/fuel mixture into the center of the combustion chamber.

This air fuel mixture is then ignited by the spark plug.

Compressor Notes: To aid in starting when the air rail pressure is low and

before the compressor has time to build pressure, some direct injectors are

held open by the PCM. This allows the compression from inside the cylinders

to pressurize the air rail faster (1 or 2 strokes, or 60

° of crankshaft rotation).

Idle Notes: Idle quality is controlled by fuel volume and fuel timing. The

throttle shutter will be open at idle speed. The shift switch is mounted on the

exhaust adaptor plate and is activated by a cam/notch in the upper shift shaft.

The switch has a closed circuit when the engine is in gear (forward or reverse)

and an open circuit when the engine is in neutral. The switch is monitored by

the PCM. The PCM will change fueling, timing and RPM limit according to

whether the engine is in gear or in neutral.

The TPS signals the PCM to change the fuel and spark without movement of

the throttle shutters. The throttle cam is manufactured to allow the TPS sensor

shaft to move before opening the throttle shutter.

Notes

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