Mariner Mercury 105/140 JET, Service Manual

Page: 224 / 797

90-824052R3 JUNE 2002 FUEL SYSTEMS - 3C-17
EFI Electrical Components (from
Electrical Component Diagram)
ELECTRONIC CONTROL MODULE (ECM)
The ECM is continually monitoring various engine
conditions (engine temperature, engine detonation
control, engine throttle opening) and climate
conditions (induction air temperature, barometric
pressure and altitude level) needed to calculate fuel
delivery (pulse width length) of injectors. The pulse
width is constantly adjusted (rich/lean conditions) to
compensate for operating conditions, such as
cranking, cold starting, climate conditions, altitude,
acceleration and deceleration, allowing the outboard
to operate efficiently at all engine speeds.
SENSOR INTERACTION WITH THE ECM
IMPORTANT: DO NOT run engine for extended
periods of time with sensors disconnected or by-
passed (shorted). Serious engine damage may
result.
AIR TEMPERATURE SENSOR
The air temperature sensor transmits manifold abso-
lute air temperature, through full RPM range, to the
ECM. As air temperature increases “sensor” resis-
tance decreases causing the ECM to decrease fuel
flow (leaner mixture). Disconnecting the air temp
sensor (open circuit) will increase fuel flow (richen
mixture) by 10%. Bypassing air temp sensor (short in
circuit) will cause fuel flow to decrease 10%.
The air temperature sensor circuit can be tested
using the EFI tester. The air temperature sensor can
be tested following air temperature sensor test on
page 3C-34.
MANIFOLD ABSOLUTE PRESSURE (MAP)
SENSOR
The MAP sensor is a non-serviceable sensor
mounted in the ECM box. The MAP sensor is used
to sense changes in manifold absolute pressure and
is connected to the intake manifold by the way of a
vacuum hose. The MAP sensor is functioning
through the full RPM range and is continually signal-
ing induction manifold pressure readings to the ECM.
The ECM in turn determines fuel flow as signals are
received. Drawing a vacuum on the MAP sensor
hose will create a lean fuel condition altering engine
operation. If no change occurs when drawing vacu-
um, MAP sensor is not functioning properly.
MAP sensor can be tested with the EFI tester.
ENGINE HEAD TEMPERATURE SENSOR
The Engine Head Temperature Sensor provides the
ECM signals related to engine temperature to deter-
mine level of fuel enrichment during engine warm up.
The ECM is receiving information at all engine tem-
peratures but stops fuel enrichment at an engine
temperature of 90
°
F (32
°
C). An open circuit on the
temperature sensor will increase fuel flow up to 40%
but will not be affected at wide open throttle. If no
change occurs when sensor is disconnected, sensor
may not be functioning properly. The engine head
temperature sensor can be tested following Engine
Head Temperature Sensor Test on page 3C-35.
NOTE: If sensor does not make clean contact with
cylinder head a rich condition may exist.
THROTTLE POSITION SENSOR (TPS)
The TPS transmits information to the ECM during low
speed and mid range operation, related to throttle
angle under various load conditions. TPS adjustment
is a critical step in engine set up (Section 2C). Dis-
connecting the TPS will increase fuel flow 40% at idle
but does not effect WOT.
NOTE: The higher the resistance the richer the fuel
flow. Refer to TPS Adjustment (Section 2C).
DETONATION CONTROL SYSTEM (200 MODEL)
The Detonation Control System consists of a
detonation control sensor located on the port side
cylinder head and a detonation control module
mounted on the engine. The detonation control
module has seven wires:
•
WHITE/BLUE - Connects to knock sensor,
transmits knock signal to control module.
•
GREEN - Connects to #2 primary wire. The
primary voltage signals the controller to monitor
combustion “noise” during a window of time (See
Detonation System Function following).
•
WHITE/BLACK - Two of these wires connect to
the switch boxes bias circuit terminals. A third
wire is spliced in one bias circuit (inner switchbox)
and connects to the idle stabilizer module. (See
complete Engine Wiring Diagram - refer to
Section 2D).
•
GRAY/WHITE - Connects to the ECM; signals
ECM to enrich fuel mixture when knocking
occurs.
•
PURPLE -12 Volt power supply.