Mercury 15 EFI FourStroke, Service Manual

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A fuel cooler is integrated within the lower housing of the VST.
62987
Throttle Body
The throttle body is connected to the intake manifold. It controls the amount of air that is allowed into the intake manifold. The
throttle body affects the manifold absolute pressure (MAP). When the throttle body valve is closed (idle), the air pressure inside
the intake manifold is in a vacuum state. When the throttle body valve opens, the vacuum condition of the intake manifold drops
proportionally to the position of the throttle body valve. At wide‑open throttle (WOT), the condition of the air inside the intake
manifold continues to be in a vacuum state, but is significantly less of a vacuum than when at an idle position. These changes
of the vacuum inside the intake manifold affect the MAP sensor reading, allowing the ECM to adjust the fuel injection quantity
and the ignition timing.
63002
Engine Control Module (ECM)
Overview
The ECM takes inputs from sensors and controls the actuators. The ECM also rectifies voltage from the stator, to supply power
to the various electrical components used on the engine, excluding the optional electric starting, charging, and power tilt
components.
The ECM is itself powered by voltage from the stator, and does not require a battery. For diagnostics, a special adapter cable
supplies the required power.
The ECM is a highly reliable component, and is rarely the source of a running issue. However, if the ECM should completely
fail, the engine will not operate.
ECM and Fuel Injection
The ECM receives inputs from the crankshaft position sensor (CPS), engine coolant temperature (ECT) sensor, temperature
and manifold absolute pressure (TMAP) sensor, and the throttle position sensor (TPS). It uses the data from these sensors to
control the fuel injectors and the idle air control (IAC) valve:
Fuel injection:
Controls the fuel injection pulse‑width (duration) for optimum efficiency according to current operating
condition
Idle air control:
Stabilizes the engine RPM when idling and during quick engine RPM deceleration by managing the duty
cycle driving the IAC in order to control bypass air entering the intake manifold
Fuel System Operation
90-8M0125265 eng NOVEMBER 2017 © 2018 Mercury Marine Page 3A-3