PleasureCraft Engine Group 5.0L, Diagnostic Manual, Page: 84 / 337

3C - 2 Fuel Metering System 8.1L
MEFI 4 - PCM
General Description
Purpose
The function of the fuel metering system is to deliver the
correct amount of fuel to the engine under all operating
conditions. Fuel is delivered to the engine by individual
fuel injectors mounted in the intake manifold near each
cylinder.
Modes Of Operation
The ECM looks at inputs from several sensors to determine
how much fuel to give the engine. The fuel is delivered under
one of several conditions, called “modes.” All the “modes” are
controlled by the ECM and are described below.
Starting Mode
When the ignition switch is turned to the crank position, the
ECM turns the fuel pump relay “ON,” and the fuel pump
builds up pressure. The ECM then checks the ECT, MAP
and TP sensors, and determines the proper air/fuel ratio
for starting. The ECM controls the amount of fuel delivered
in the starting mode by changing how long the injectors
are turned “ON” and “OFF.” This is done by “pulsing” the
injectors for very short times.
Clear Flood Mode
If the engine fl oods, it can be cleared by opening the throttle
to 100% (wide open throttle) during cranking. The ECM then
shuts down the fuel injectors so no fuel is delivered. The
ECM holds this injector rate as long as the throttle stays
at 100%, and the engine speed is below 300 RPM. If the
throttle position becomes less than 100%, the ECM returns
to the starting mode.
Run Mode
When the engine is fi rst started and RPM is above 300 RPM,
the system operates in the run mode. The ECM will calculate
the desired air/fuel ratio based on these ECM inputs: RPM,
ECT and MAP. Higher engine loads (MAP input) and colder
engine temperatures (ECT input) require more fuel, or a
richer air/fuel ratio.
Acceleration Mode
The ECM looks at rapid changes in TP sensor and MAP,
and provides extra fuel by increasing the injector pulse
width.
Fuel Cutoff Mode
No fuel is delivered by the injector when the ignition is “OFF,”
to prevent dieseling. Also, injector pulses are not delivered if
the ECM does not receive distributor reference pulses, which
means the engine is not running. The fuel cutoff mode is also
enabled at high engine RPM, as an overspeed protection for
the engine. When fuel cutoff is in effect due to high RPM,
injector pulses will resume after engine RPM drops below the
maximum OEM RPM specifi cation (Rev Limit).
Power Reduction Mode
Power reduction mode is a function of the ECM that reduces
engine power under certain conditions. Power reduction will
disable one fuel injector driver when the engine speed goes
above 2500 rpm, and enable the fuel injector driver when
the engine speed drops below 1200 rpm. Power reduction
may be active for the following conditions:
•
Engine coolant temperature too high
•
Low oil pressure
•
Transmission temperature too high (if applicable)
Fuel Metering System Components
The fuel metering system (Figure 3-1) is made up of the
following parts:
•
Fuel supply components (fuel tank, pump, lines, fi lter).
•
Fuel pump electrical circuit.
•
Fuel rail assembly, including fuel injectors and pressure
regulator assembly.
•
Throttle body assembly, including an IAC valve and
TP sensor.
Fuel Supply Components (FCC System)
The Fuel Control Cell (FCC) incorporates two (2) fuel
pumps to provide uninterrupted fl ow of fuel to your marine
engine.
Fuel is fed into the FCC by a low-pressure, high volume
electric fuel pump. This pump fl ows fuel at a volume which
exceeds the fuel fl ow rate required of the high-pressure
pump by engine demands.
The high pressure pump, mounted inside the FCC bowl,
provides the necessary fuel pressure and volume to maintain
proper engine performance, and always has an ample
supply of fuel to meet the idle, cruise and acceleration fuel
requirements of the engine.
The fuel pressure regulator, located on the fuel rail, controls
fuel pressure and maintains a constant pressure across the
fuel delivery system. Fuel not used by the engine, excess
fuel, is returned to the FCC canister.
The fuel delivered to the engine by the FCC is fi ltered by a
fi lter and water separator element, which surrounds the high
pressure pump inside the FCC bowl.
The fuel enters the FCC bowl from two (2) components,
the low-pressure pump (initial input) and the fuel pressure
regulator (unused recirculating). Fuel exits the FCC bowl at
two (2) locations, the high-pressure output to the fuel rail
and all excess fuel in the FCC bowl is routed back to the
fuel tank via a return line.
Quick-Connect Fittings
Quick-Connect fi ttings provide a simplifi ed means of
installing and connecting fuel system components. The
fi ttings consists of a unique female connector and a
compatible male pipe end. O-rings, located inside the
female connector, provide the fuel seal. Integral locking
tabs inside the female connector hold the fi ttings together.