Electronic Control Modules (ECM) are used to control the engine. Each module is an environmentally sealed unit that is mounted in a terminal box on the engine. The following modules are standard:
Master ECM - The master ECM controls most of the functions of the engine. The master ECM monitors various inputs from sensors in order to activate relays, solenoids, etc at the appropriate levels. The master ECM supports the following primary functions:
- Engine speed governing
- Air/fuel ratio control
- Start/stop sequencing
- Engine monitoring and protection
- Control of the ignition and detonation of the left cylinder bank
Slave ECM - The slave ECM supports the control of ignition and of detonation of the right cylinder bank.
The master ECM and the slave ECM communicate via the Cat Data Link.
The master ECM contains the logic and the outputs for control of engine starting and of engine shutdown. Program this logic through the configuration screens that are in Caterpillar Electronic Technician (ET). The logic responds to signals from the following components:
- Engine control switch
- Emergency stop switch
- Remote start switch
- Data link
- Prelubrication system
- Other inputs
When the programmable logic determines that it is necessary to crank the engine, the ECM supplies +Battery voltage to the relay for the starting motor. The ECM removes the voltage when the programmable crank terminate speed is reached or when a programmable cycle crank time has expired.
The engine must be equipped with an energize-to-run Gas Shutoff Valve (GSOV). The source of the voltage to the GSOV depends on the engine's configuration. The GSOV may be energized by the customer's equipment or by the engine's control system.
If the engine's control system controls the GSOV, the ECM supplies +Battery voltage to the GSOV whenever the programmable logic determines that fuel is required to operate the engine.
For more information on programmable parameters, see Troubleshooting, "Programming Parameters".
The ECM provides variable ignition timing that is sensitive to detonation.
Each cylinder has an ignition transformer that is located under the valve cover for the cylinder. To initiate combustion, the ECM sends a pulse of approximately 100 volts to the primary coil of each ignition transformer at the appropriate time and for the appropriate duration. The transformers step up the voltage in order to create a spark across the spark plug electrode.
Detonation sensors monitor the engine for excessive detonation. The engine has detonation sensors that monitor each cylinder. The sensors generate data on vibration that is processed by the ECM in order to determine detonation levels. If detonation reaches an unacceptable level, the ECM retards the ignition timing of the cylinder that is experiencing the detonation. If retarding the timing does not limit detonation to an acceptable level, the ECM shuts down the engine. The maximum timing retard that is allowed due to detonation is six degrees from the desired timing.
The ECM provides extensive diagnostics for the ignition system. The ECM also has an input that is used to toggle between different settings for the ignition timing. This allows the engine to be easily converted for use with alternate fuels.
The ECM maintains the desired engine speed by controlling the electronic actuator for the throttle. The actuator is located above the air inlet manifold.
The actuator is electrically controlled and electrically actuated. The ECM sends a throttle command to the actuator via the CAN data link. The actual throttle position can be determined by comparing a scribe mark on the throttle shaft with the increments on a protractor. The throttle position may also be viewed in Cat ET.
Desired engine speed is determined by the status of the idle/rated switch, the desired speed input (analog voltage or 4 to 20 mA), and parameters such as maximum engine high idle speed that are programmed into the ECM. Actual engine speed is detected via a signal from the speed/timing sensor. Parameters such as governor gain that controls the engine stability can be programmed via the configuration screens that are in Cat ET.
Engine Monitoring and Protection
The ECM monitors both the engine operation and the electronic control system.
Problems with engine operation such as low oil pressure produce an event code. The ECM can issue a warning or a shutdown for a low oil pressure event. This depends on the severity of the condition.
The engine is equipped with an Advisor Monitor Display. The Advisor module and the engine ECM communicates via the Cat Data Link. Engine status and engine diagnostics can be viewed with the Advisor module.
For information that relates to system overview of the engine monitoring system, refer to Troubleshooting, "Engine Monitoring System".
For information that is related to the monitoring system parameters for this engine, refer to Troubleshooting, "Event Codes".
For information that is related to troubleshooting event codes that are active or logged, refer to Troubleshooting, "Event Codes".
Problems with the electronic control system such as an open circuit produce a diagnostic code. For more information, refer to Troubleshooting, "Diagnostic Trouble Codes".
This system consists of an electronic fuel metering valve, output drivers in the ECM, and maps in the ECM. The ECM compensates for changes in the BTU of the fuel in order to maintain desired emission levels. The ECM provides control of the air/fuel mixture for maximum performance and for efficiency at low emission levels. The system is dependent on information from the following inputs:
- Status of various sensors
- Status of some output drivers in the ECM
- Control maps in the ECM
- Parameter settings that have been entered via the configuration screens in Cat ET
To accurately control the air/fuel ratio, the ECM depends on the following parameters that are programmed via the "Configuration" screen of Cat ET. For details on these parameters, refer to Systems Operation/Testing and Adjusting, "Electronic Control System Parameters".
- "Air/Fuel Integral Gain"
- "Air/Fuel Proportional Gain"
- "Desired Engine Exhaust NOx Level Setting"
- "Emissions Feedback Mode Configuration"
- "Fuel Specific Heat Ratio"
- "Fuel Quality"
- "Gas Specific Gravity"
The system consists of an electronic fuel metering valve, output drivers in the ECM, and maps in the ECM. The ECM compensates for changes in the BTU of the fuel in order to maintain desired emission levels.
Refer to Systems Operation/Testing and Adjusting for information that is related to the operation of the air/fuel ratio control for your engine.
Optional Prelubrication and Post Lubrication
The prelubrication system consists of an oil pressure sensing switch and a prelubrication pump. The ECM controls the prelubrication pump in order to raise the oil pressure to a sufficient level prior to cranking the engine.
The strategy for post lubrication begins as the engine coasts after shutdown. This ensures that the bearings that are for the turbocharger shaft have adequate lubrication during the engine deceleration as the engine coasts to a stop.
The following parameters are used to configure the prelubrication system:
- "Engine Pre-lube"
- "Engine Pre-lube Time Out Period"
- "Engine Post-lube Time Out Period"