20189 Mercury SCREW, COVER TO BOTTOM COWL (3/4")

Engine Speed/Timing Input Circuit
Engine speed is sensed by an electronic sensor. The same sensor is used for monitoring the position of the camshaft. The engine speed/timing sensor creates signals as the timing reference ring rotates past the sensor's pickup (sliphead). The timing reference ring is mounted on the rear of the left camshaft. A unique tooth pattern on the timing reference ring allows the ECM to determine the crankshaft position, the direction of rotation, and the speed. The ECM supplies the engine speed/timing sensor with 12.5 1.0 VDC which is required for proper operation.The output of the engine speed/timing sensor is a series of pulses. The frequency of the pulses is dependent upon the speed of the engine. The ECM interprets the frequency of the pulses as engine speed. The shape of the pulses is dependent upon the rotation position of the camshaft. The ECM reads the shape of the pulses in order to determine the position of the camshaft.Coolant Temperature Input Circuit
The temperature of the engine coolant is measured by an electronic sensor. The sensor is mounted on the cover of the regulator housing. The signal from the sensor is used to modify the fueling of the engine. The signal is also used to modify the timing for an improved cold start and for reduction in white smoke. The ECM supplies the coolant temperature sensor with 5.0 0.5 VDC. The sensor's output voltage is 0.2 4.6 VDC. This depends on the temperature of the engine's coolant.Throttle Position Input Circuit
The throttle position is obtained from an electronic sensor that is connected to the throttle pedal. The 8.0 0.5 VDC operating voltage is provided to the sensor by the electronic control module (ECM).The output of the throttle position sensor is a constant frequency signal with voltage levels of 0 or 10 volts. The pulse width is not the frequency of the signal. The pulse width of the signal is dependent upon the arm rotation of the throttle position sensor. The pulse width is interpreted by the ECM as the throttle position. The minimum duty cycle is between 10 and 22 percent. The maximum duty cycle is between 44 and 52 percent. The ECM interprets the minimum duty cycle as 0 percent of the throttle position. The ECM interprets the maximum duty cycle as 100 percent of the throttle position.The throttle position sensor is integrally mounted to the throttle pedal assembly. The throttle position sensor rotates approximately 18 degrees from the low idle stop to the high idle stop on the pedal assembly. The electronic control system will automatically calibrate any of the deadband in the throttle pedal. This occurs as the pedal is actuated throughout the range of travel. Mechanical stops on the pedal assembly restrict the rotation of the throttle sensor. This helps prevent damage to the sensor. The mechanical stops eliminate the need to manually adjust the pedal stops.Injector Output Circuits
An electrical signal from the ECM controls each electronic unit injector (EUI). This electrical signal determines the fuel injection timing. The duration of the electrical signal determines the quantity of fuel that is injected. The signal allows precise control of the injectors.Atmospheric Pressure Input Circuit
Atmospheric pressure is monitored by the atmospheric pressure sensor. The sensor is located on the mounting bracket for the ECM. A 5.0 0.5 VDC supply voltage is provided by the ECM. The output of the atmospheric pressure sensor is a DC signal. This signal has a range from 0.2 volts to 4.8 volts. The ECM interprets the output voltage as atmospheric pressure.Turbocharger Inlet Pressure Circuit
The air pressure in the air induction system for the engine is monitored by the turbocharger inlet pressure sensors. The sensors are located in each air inlet tube. The ECM provides the sensor with a 5.0 0.5 VDC supply voltage. The output of the turbocharger inlet pressure sensor is a DC voltage signal. The signal has a range from 0.2 volts to 4.8 volts. The ECM interprets the signal from this sensor as the inlet air pressure to the turbocharger compressors.Turbocharger Outlet Pressure Circuit
The engine's air inlet manifold pressure is monitored by the turbocharger outlet pressure sensor. The sensor is located at the front of the engine. The sensor is mounted in a block on the bracket of the front water regulator housing. The sensor receives a 5.0 0.5 VDC supply voltage from the ECM. The output of the sensor is a DC signal. The signal has a range from 0.2 volts to 4.8 volts. The signal is interpreted by the ECM as the absolute pressure of the inlet manifold.Elevated Low Idle Override
Under some ambient operating temperatures without increased engine speed, the machine will not reach the proper operating temperature after start-up. This is due to the cooling capacity of the machine. The machine will cool below the proper operating temperature during idling.The elevated idle is enabled when the transmission is in neutral and the parking brake is engaged. Neutral status and parking brake status are based on inputs over the data link. These inputs are from the transmission control. The activation of the elevated idle is delayed on the engine start-up or on the engine cooldown.Air Filter Restriction
The air filter restriction is indicated by the monitoring control module when the pressure drop across the air cleaner filters exceeds the maximum allowable level that is recommended by Caterpillar. The monitoring control module receives the air restriction warning from the ECM through the data link.Engine Overspeed Lamp and Alarm Output
The ECM provides a signal to the machine's monitoring panel via the data link. This signal indicates whether the engine speed is at an acceptable level. A warning is indicated on the monitoring panel. The warning is indicated with an action lamp and an alarm. Overspeed is activated when engine speed exceeds 2100 rpm. The warning remains active until the engine speed decreases to 1900 rpm. Low Oil Pressure Warning
The ECM provides a signal to the machine's monitoring panel via the data link .