Dfi Operation; Air Induction; Air Compressor System; Fuel - Mercury 200 OptiMax Jet Drive Service Manual

Direct Fuel Injection

DFI Operation

Air Induction

Air enters the cowl through holes in the top aft end of the cowl. The cowl liner directs the air to the bottom of the powerhead. This
limits salt exposure to the engine components. Air volume entering the plenum is controlled with the throttle body shutter mounted
on the plenum. The throttle body shutter is actuated by the throttle cam. When the throttle body shutter opens, the air passes
through the reed valves and into the crankcase. The throttle position sensor (TPS) is mounted on a support plate and is connected
to the throttle cam by a link shaft. The TPS transmits throttle angle information to the propulsion control module (PCM).

Air Compressor System

Air from inside the engine cowl is drawn into the compressor through the flywheel cover. This cover acts like a muffler to quiet
compressor noise and contains a filter to prevent the ingestion of debris into the compressor. The compressor is driven by a belt
from a pulley mounted on the flywheel and is automatically self‑adjusted with an idler pulley. This air compressor is a single cylinder
unit containing a connecting rod, piston, rings, bearings, reed valves, and a crankshaft. The compressor is water‑cooled to lower
the temperature of the air charge and is lubricated by oil from the engine oil pump assembly. As the compressor piston moves
downward inside the cylinder, air is pulled through the filter, reed valves and into the cylinder. After the compressor piston changes
direction, the intake reeds close and the exhaust reeds open allowing compressed air into the hose leading to the air/fuel rails.
The air compressor is designed to deliver a charged air pressure significantly higher than what is required for the engine to operate
efficiently. Inside the fuel rail, an air pressure regulator limits the charged air to a specific pressure that is lower than the pressure
of the fuel. The excess air pressure is dumped into the adapter plate.

Fuel

IMPORTANT: Due to the inconsistent fuel quality in some areas, excessive fuel system and combustion chamber deposits are
on the rise. These deposits cause many driveability problems that range from hesitation, rough idle, spark plug fouling, to
detonation problems. This performance characteristic can be greatly reduced through regular fuel system maintenance.
To minimize fuel system and carbon deposit buildup in the engine, it is strongly recommended to add Mercury/Quicksilver
Quickleen Engine Treatment (or equivalent) to your engine's fuel at each tank fill throughout the boating season. Use additive as
directed on the container.
Fuel for the engine is stored in a fuel tank. An electric lift pump assembly is installed into the fuel line for priming the fuel system
and supplies fuel to the low‑pressure boost pump. The low‑pressure boost pump mounted on the vapor separator tank, then
pushes the fuel through a water separating fuel filter. This filter removes contaminants and water before the fuel reaches the vapor
separator tank. Fuel vapors are vented through a hose into the air compressor inlet on the front of the flywheel cover. The electric
fuel pump (inside the VST) is different than the fuel pump that is utilized on the standard EFI engine (non‑DFI), and is capable of
developing fuel pressures in excess of 751.5 ± 14 kPa (109 ± 2 psi). Fuel inside the rail must remain pressurized at exactly
103.5 kPa (15 psi) over the air rail pressure or the PCM (map) calibrations will be incorrect. Fuel from the vapor separator is
supplied to the bottom of the starboard fuel rail. A fuel line connects the bottom of the first rail to the opposite fuel rail. Fuel is
stored inside the rail until an injector opens. A fuel pressure regulator controls pressure in the fuel rails, and allows excess fuel to
return into the vapor separator. The fuel regulator not only regulates fuel pressure, but also regulates it at approximately 10 psi
higher than whatever the air rail pressure is. The fuel regulator diaphragm is held closed with a spring that requires 103.5 kPa
(15 psi) to force the diaphragm off the diaphragm seat. The backside of the diaphragm is exposed to air rail pressure. As the air
rail pressure increases, the fuel pressure needed to open the regulator will equally increase. Example: If there is 345 kPa
(50 psi) of air pressure on the air rail side of the diaphragm, 448 kPa (65 psi) of fuel pressure will be required to open the regulator.
The port fuel rail is water‑cooled.
To equalize the pulses developed by the pumps (both air and fuel) a tracker diaphragm is installed in the starboard rail. The tracker
diaphragm is positioned between the fuel and air passages. The tracker diaphragm is a rubber diaphragm which expands and
retracts depending upon which side of the diaphragm senses the pressure increase (pulse).

Oil

Oil is not mixed with fuel before entering the combustion chamber. The oil is stored inside the reservoir. Oil flows from the oil
reservoir to the oil pump. The oil pump is mounted on the powerhead. The oil pump is a solenoid‑driven pump, actuated by the
PCM and includes seven pistons with discharge ports. The oil is discharged into the crankcase and lubricates each cylinder. The
seventh passage lubricates the air compressor. Excess oil from the compressor returns into the cylinder bores.
The PCM will change the discharge rate of the oil pump depending upon engine demand. The PCM energizes the pump on initial
start‑up to fill the oil passages eliminating the need to bleed the oil system. The PCM provides additional oil for the break‑in. The
break‑in time is determined by the PCM internal clock.

Electrical

The electrical system consists of the PCM, crankshaft position sensor, throttle position sensor, manifold absolute pressure sensor,
engine temperature sensor, ignition coils, fuel injectors, and direct injectors. The engine requires a battery to start and will not run
off of the alternator.
Page 3B-22 90-8M0050731 MAY 2011