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Electronic Control Module (ECM)
The ECM is the center of the engine control system. The ECM governs engine speed by controlling the electrical signals to the injector solenoids.Air Inlet Heater Operation
Background
The Air Inlet Heater is used to improve the cold start capability of the engine and to reduce white smoke. The ECM controls the Air Inlet Heater Grid through the Air Inlet Heater Relay.The Air Inlet Heater operation is determined at three different times (Power Up/Preheat, Cranking, and Engine Started Cycle) based on various engine parameters.ECM Power Up and Preheat Cycle
If the Coolant Temperature is less than 49°C (120°F), the ECM will turn the heater ON for 30 seconds as a preheat cycle.The Heater should turn ON, and then OFF when the cycle is complete. If the operator attempts to start the engine before the 30 second preheat cycle ends the ECM begins using the strategy for the Cranking Cycle.Cranking Cycle
When the engine is cranking, the Heater will turn ON if the Coolant Temperature is less than 49°C (120°F), and stay ON while cranking. If the engine fails to start the Heater will activate for 30 seconds (preheat cycle is restarted).Engine Start Cycle
After the engine has started, the Heater operation is determined by the Coolant Temperature.If the coolant temperature is less than 49°C (120°F), the Engine Start Cycle begins. The Engine Start Cycle has two segments, a continuous mode followed by an On/Off cycling mode. The Continuous On mode lasts for a maximum of five minutes. The On/Off cycle mode can last for a maximum of 15 minutes. During the On/Off cycle mode, the Heater is cycled ON and OFF for ten seconds. The Air Inlet Heater will turn OFF anytime the Coolant Temperature exceeds 49°C or 120°F.Figure 17 - Air Inlet Heater Operation Chart Engine Speed/Timing Sensors
The 3126B engine uses two Engine Speed/Timing Sensors, both detecting engine speed and timing reference from a unique pattern on the camshaft gear. The ECM calculates the time between pulses created by the sensor as the camshaft gear rotates to determine engine speed. The ECM stores the pattern of the pulses and compares the signal pattern to the expected pattern to determine crankshaft position. After locating No. 1 cylinder, the ECM triggers each injector in the correct firing order and at the correct time. The actual timing and duration of each injection is based on engine speed and load. A loss of signal from one of the sensors will not cause noticeable engine operation changes. The loss of the signal from both sensors will result in the ECM terminating injection and shutting down the engine, or preventing it from starting.Both sensors are magnetic sensors with and integral connector. They must be serviced as a pair. If one requires replacement, they must both be replaced. The two sensors are not interchangeable, do not switch sensor positions. The Top Camshaft Sensor (Sensor #1) must be connected to the engine harness with the black harness connector and the Bottom Camshaft Sensor (Sensor #2) must be connected to the grey harness connector. If the sensors are replaced, a timing calibration in NOT necessary for the 3126B Marine Engine. Timing calibration is only necessary after replacing an ECM.Repair any Speed/Timing Sensor faults at the earliest possible opportunity to prevent unscheduled engine down time.Boost Pressure Sensor
The Boost Pressure Sensor measures the absolute pressure in the inlet air manifold.The boost pressure is calculated by the ECM to control the fuel to air ratio. The boost pressure is communicated over the data link and on the Electronic Service Tool.The Boost Pressure Sensor measures pressure from 20 to 340 kPa (3 to 49 psi). The sensor is supplied with 5 VDC by the ECM.Injection Actuation Pressure Sensor
The Injection Actuation Pressure Sensor provides an injection actuation pressure signal to the ECM. The ECM modifies the current to the Injection Actuation Pressure Control Valve to control the injection and actuation pressure. Desired injection actuation pressure is based on fuel quantity, injection timing, engine speed, and engine operating mode (cold versus warm mode).The Injection Actuation Pressure Sensor is supplied with 5.0 VDC by the ECM. The sensor returns a voltage signal to the ECM that varies between 0 and 4.8 VDC. The operating range of the sensor is 400 to 31000 kPa (58 to 4496 psi).Injection Actuation Pressure Control Valve
The Injection Actuation Pressure Control Valve regulates the high pressure oil system that drives the hydraulic electronic unit injectors. The Injection Actuation Pressure Sensor indicates the actual injection actuation pressure to the ECM.The ECM sends a pulse width modulated signal to the Injection Actuation Pressure Control Valve. The ECM adjusts this signal to the injection actuation pressure control valve to maintain the desired actuation pressure. The current of the signal varies between 0 and 800 milliamperes.The ECM calculates the desired injection actuation pressure based on the calculated fuel quantity, injection timing, engine speed, and the engine operating mode. The engine operating mode is either the cold mode or the warm mode.The Injection Actuation Pressure Control Valve Signal is Pulse Width Modulated and operates between 0 and 800 milliamperes.Coolant Temperature Sensor
The standard Coolant Temperature Sensor is used to monitor engine coolant temperatures. The engine response to high coolant temperature is determined by a customer programmable parameter on the Service/Monitoring System Screen.Cold Mode
The ECM uses the coolant temperature to determine the cold mode operation. When the engine control system is in cold mode, the following characteristics of engine operation are changed to improve operation of a cold engine:* The timing is advanced.* The actuation pressure for fuel injection is increased.* The fuel quantity is limited.The cold mode operation is activated whenever the coolant temperature is below 18 °C (64 °F). The cold mode remains active until one of the following changes occurs:* The coolant temperature increases above 18 °C (64 °F).* The engine has been running for a period of 12 minutes.