Product Manual

Troubleshooting
For troubleshooting information, refer to:
•
Section 1E ‑ Accessing ECM Information with CDS G3
•
The appropriate engine wiring diagram in Section 9A ‑ Color Diagrams
Additional Information
For additional information on the ECM, including removal and installation procedures, refer to Section 2A ‑ Engine Control
Module (ECM).
Sensors
This engine uses sensors to monitor various aspects of engine operation. The data from these sensors are vital to controlling
optimum fuel efficiency, horsepower, and emissions. The engine control module (ECM) uses sensor data to manage the fuel
system, ignition system, and operator warning system.
The following brief descriptions are of each sensor that contributes to fuel system operation. For additional details, including
service procedures and troubleshooting information, refer to Section 2A ‑ Sensors.
Crankshaft Position Sensor (CPS)
The crankshaft position sensor (CPS) is a hall effect switch. It is located at the top of the cylinder block, next to the flywheel.
The CPS generates a pulse for each revolution of the crankshaft. Each pulse is sent to the ECM. The timing and frequency of
the pulse allows the ECM to regulate ignition and fuel injector timing.
If the CPS fails, the engine will run rough or stop running.
Engine Coolant Temperature (ECT) Sensor
The engine coolant temperature sensor is located on the top of the cylinder block. It monitors the temperature of the engine
coolant. The ECM uses this data in the calculations for setting the fuel delivery volume.
If the sensor indicates an overtemperature condition, the ECM issues a warning to the operator via the warning buzzer and
warning light for the duration of the overtemperature state.
If the sensor fails or becomes disconnected, engine speed will be limited to 2800 RPM.
Temperature and Manifold Absolute Pressure (TMAP) Sensor
This sensor unit combines two sensors in one housing. The two sensors are the manifold air temperature (MAT) sensor and the
manifold absolute pressure (MAP) sensor.
The MAT sensor is a thermistor that monitors the temperature of the intake air as it exits the throttle body and enters the intake
manifold. The ECM sets the fuel injection volume to allow the engine to run at optimum efficiency, based in part on the MAT
data.
The MAP sensor monitors the air pressure of the intake air as it exits the throttle body and enters the intake manifold. The ECM
compares the current manifold absolute pressure to the ambient atmospheric pressure (measured at start‑up), and then makes
adjustments to the fuel injection volume, based in part on this MAP data.
If the sensor unit fails or becomes disconnected, engine speed will be limited to 2800 RPM.
Throttle Position Sensor (TPS)
The throttle position sensor (TPS) is located on the throttle body and is in direct contact with the throttle shaft. The TPS
transmits throttle angle information to the ECM, which regulates the fuel injector volume (pulse width) and ignition timing.
Should the sensor fail, a warning horn will sound and the engine RPM will be reduced by the ECM.
Actuators
Function of Actuators
Actuators receive output signals from the ECM, and perform functions which control air‑fuel ratios, spark advance, and idle
RPM. The actuators maintain optimal fuel economy as a direct relation to the engine horsepower.
Idle Air Control (IAC)
The idle air control (IAC) valve, sometimes referred to as the idle speed control valve (ISCV), is an electrically operated
spring‑loaded solenoid valve that controls the amount of air bypassing the closed throttle shutter. Signals from the ECM
regulate the duty cycle for which the IAC valve remains open or closed. The IAC valve controls three operating functions:
•
Provides additional intake air for the engine during start‑up, and allows increased idle RPM during engine warm‑up.
• Controls idle speed according to the varying engine loads and running conditions.
Fuel System Operation
Page 3A-4 © 2018 Mercury Marine 90-8M0125265 eng NOVEMBER 2017