Mariner Mercury 105/140 JET, Service Manual

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90-824052R3 JUNE 2002 FUEL SYSTEMS - 3D-17
Fuel Flow Component
Description
Pulse Fuel Pump
The pulse fuel pump operates through alternating
crankcase pressure to deliver fuel through the water
separating filter to the vapor separator.
Fuel pressure @ Idle – 2-3 psi (Minimum – 1 psi).
Fuel Pressure @ Wide-Open-Throttle – 6-8 psi (Mini-
mum – 4 psi).
Water Separating Filter
The water separating filter protects the fuel injectors
from water and debris. The filter contains a sensor
probe which monitors water level in the filter. If water
is above the sensor probe, the water detection light
will come on and the warning horn will begin a series
of beeps.
Vapor Separator
The vapor separator is a fuel reservoir which
continuously blends and circulates fresh fuel, oil and
unused fuel/oil from the fuel rail.
a. Fuel Inlet – Fresh fuel delivered from the
water separator by the crankcase mounted
pulse fuel pump. The amount of fuel allowed
to enter the vapor separator is controlled by
a needle/seat and float assembly mounted in
the cover of the vapor separator.
b. Oil Inlet – Oil delivered by the crankshaft
driven oil pump.
c. Crankcase Bleed Inlet – Recirculated
(unburned) fuel/oil mixture delivered from the
bleed lines through a filter into the vapor
separator.
d. Fuel Pressure Regulator Inlet – Unused fuel/
oil mixture being recirculated from the fuel rail
back into the vapor separator.
Bleed System
On carbureted engines, excess fuel which collects in
the crankcase is channeled into the transfer ports to
be burned.
On EFI engines, excess crankcase fuel is directed
through a filter (to eliminate contaminates) and
emptied into the vapor separator. It mixes with fresh
incoming fuel and is pumped to the fuel rail and fed
through the injectors.
A 30 micron filter is installed in the bleed line to
prevent contaminants from entering the vapor
separator. If the filter becomes clogged, the engine
will load up at idle and hesitate upon acceleration.
Final Filter
The final filter is located below the electric fuel pump
in the vapor separator. The filter collects debris and
prevents them from flowing through the electric pump
and into the fuel rail and injectors.
Electric Fuel Pump
The electric fuel pump runs continuously while
providing fuel in excess of engine demands. The
excess fuel is circulated through the fuel rail to the
fuel pressure regulator and back to the vapor
separator.
Fuel Injectors
The fuel injectors are located inside the induction
manifold on the fuel rail. The injector valve body
consists of a solenoid actuated needle and seat
assembly. The injector receives signals from the EFI
Electronic Control Module. These signals determine
how long the needle is lifted from the seat (pulse
width) allowing a measured fuel flow. The pulse width
will widen (richer) or narrow (leaner) depending on
various signals received from sensors connected to
the EFI ECM. The ECM receives signals from the
primary ignition circuit of cylinders #1, #3 and #5 to
fire each pair of injectors accordingly.
A four wire harness connects the fuel injectors to the
ECM. The RED wire is at 12 volts and connects to all
injectors. The BLUE, YELLOW and WHITE wires
each go to a pair of injectors and are normally at 12
volts for a zero differential. To fire the injectors this
voltage is brought down to near ground creating a
potential across the injectors.