Mercury 200 OptiMax Jet Drive, Service Manual, Page: 186 / 391

Direct Fuel Injection
90-8M0050731 MAY 2011 Page 3B-23
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 ECM will receive a
signal from the throttle position sensor (TPS), engine temperature sensor, and the crankshaft position sensor (flywheel speed and
position sensor). With this information the ECM 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 ECM opens the fuel injector, high‑pressure 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:
On initial start‑up, some direct injectors are held open by the PCM to allow the compression from inside the
cylinders to pressurize the air rail faster within one or two strokes, or 60° of crankshaft rotation.
Idle notes:
Idle quality is controlled by fuel volume and fuel timing. The shift switch is mounted on the exhaust adapter plate and
is activated by a cam/notch in the upper shift shaft. The PCM monitors the switch and will change fueling, timing, and RPM limits
according to whether the engine is in gear or in neutral.
The TPS signals the ECM 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.