The ECM consists of two main components, the control computer (hardware) and the flash file (software). The control computer consists of a microprocessor and electronic circuitry. The flash file contains the engine's operational characteristics. The operating maps influence the engine's performance.
The engine ECM governs engine speed. The engine ECM and the flash file work together by controlling the amount of fuel that is delivered by the injectors. Desired engine rpm is determined by the throttle position sensor signal and certain sensor readings. Diagnostic codes may derate the engine. Actual engine rpm is measured by the engine speed/timing sensor.
The engine ECM controls the timing and the duration of the fuel that is injected. The engine ECM varies the signals to the fuel injectors. Fuel is injected only while an injector solenoid is energized by a 105 volt signal from the engine ECM. The timing of the injection signal determines the engine timing. The length of the injection signal determines engine speed. By controlling the timing and duration of the 105 volt signal, the ECM controls the engine speed.
Injection timing depends on the desired engine rpm and on the load. The ECM detects the top center position of each piston. The ECM sends an injection signal at the desired time.
During a cold start or extended periods at low idle, the engine ECM will automatically turn off one unit injector at a time in order to determine if the cylinder is firing. If the ECM determines that the cylinder is not firing, the ECM turns off the unit injector. If the ECM determines that the cylinder is firing, the ECM turns on the unit injector. This strategy improves engine starting. This strategy reduces the following: white smoke, the use of ether injection and warm-up time.
Cold mode controls fuel injection timing when the engine is cold. When the engine is cold, controlling the fuel injection timing reduces the possibility of engine damage. When the engine is cold, controlling the fuel injection timing helps minimize white smoke.
Cold mode is activated whenever the engine coolant temperature is below
The flash file inside the engine ECM sets certain limits on the amount of fuel that can be injected. The FRC limit is a limit that is based on the boost pressure. The boost pressure is calculated as the difference in pressure between atmospheric pressure and turbocharger outlet pressure. The FRC limit is used to control the air/fuel ratio for control of emissions. When the engine ECM senses a higher boost pressure, the engine ECM increases the FRC limit. A higher boost pressure indicates that there is more air in the cylinder. When the engine ECM increases the FRC limit, the engine ECM allows more fuel into the cylinder.
The rated fuel position is a limit that is based on the power rating of the engine. The rated fuel position is similar to the rack stops and the torque spring on a mechanically governed engine. The rated fuel position determines maximum power and torque values for a specific engine family and for a specific rating. The rated fuel position is programmed into the flash file at the factory.
"Multi-Torque" and "Dual Horsepower" Selection (if applicable)
This feature permits the use of different torque maps for different transmissions. The feature reduces the number of software part numbers that are required for operation. The feature protects the transmission from excessive torque.
The selection of "Multi-Torque" and "Dual Horsepower" is available through Caterpillar Electronic Technician (ET). If you select "Dual Horsepower", the engine ECM will use the low power default torque map for all transmission gears. If you select "Multi-Torque", the engine ECM will request the serial number of the transmission from the transmission ECM.
Note: If the transmission ECM does not communicate with the engine ECM, the engine ECM will use the low power default torque map. You may think that the low power is an engine problem. The problem is really the failure of communications between the transmission ECM and the engine ECM. Cat ET will continue to display "Multi-torque" on the Cat ET configuration screen in this circumstance. Power down the machine and then restart the machine. The ECM will then reset the display to the default "Dual Horsepower" configuration.
Block Diagram of Electronic Governor
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| Illustration 1 | g01206901 |
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Typical schematic | |
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| Illustration 2 | g01206905 |
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Typical schematic | |
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| Illustration 3 | g01595904 |
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| Illustration 4 | g01206909 |
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Typical schematic | |
Location of the 3512C Engine Sensors
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| Illustration 5 | g01208645 |
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Front and Left view (1) Turbocharger compressor outlet pressure sensor (boost) (2) Aftercooler temperature sensor (front) (3) Right turbocharger compressor inlet pressure sensor (4) Coolant temperature sensor (6) Left exhaust temperature sensor (5) Left turbocharger compressor inlet pressure sensor (7) Fuel filter differential pressure switch (8) Filtered engine oil pressure sensor (9) ECM connector J1/P1 (10) Machine connector (11) Connection for the prelube (12) Connector for the remote shutdown (13) Low oil level switch (14) Unfiltered engine oil pressure sensor (15) Atmospheric pressure sensor (16) ECM connector J2/P2 (17) Engine speed/timing sensor | |
Location of the 3512C Engine Sensors
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| Illustration 6 | g01208648 |
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Rear and Right view (18) Aftercooler temperature sensor (rear) (19) Right exhaust temperature sensor (20) Connector for the wastegate solenoid (21) Timing calibration plug (22) Crankcase pressure sensor (23) Connector for the engine oil renewal solenoid (24) Coolant flow switch | |