System Operation
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| Illustration 1 | g01622271 |
(1) Electronic Unit Injector (2) Solenoid for the Fuel Rail Pump (3) Secondary Speed/Timing Sensor (4) Fuel Rail Pump (5) Primary Speed/Timing Sensor (6) Intake Manifold Pressure Sensor (7) Fuel Rail Pressure Sensor (8) Engine Oil Pressure Sensor (9) Intake Manifold Temperature Sensor (10) Coolant Temperature Sensor (11) Diagnostic Connector (12) Electronic Control Module (ECM) | |
The C6.6 engine was designed for electronic control. The engine has an Electronic Control Module (ECM), a fuel rail pump and electronic unit injectors. All of these items are electronically controlled. There are also a number of engine sensors. The ECM controls the engine operating parameters through the software within the ECM and the inputs from the various sensors. The software contains parameters that control the engine operation. The parameters include all of the operating maps and customer selected parameters.
The electronic system consists of the ECM, the engine sensors and inputs from the control panel. The ECM is the computer. The personality module is the software for the computer. The personality module defines the following characteristics of the engine:
- Engine power
- Torque curves
- Engine speed (rpm)
- Engine Noise
- Smoke and Emissions
Engine Speed Governor
The ECM determines the injection timing and the amount of fuel that is delivered to the cylinders. These decisions are based on the actual conditions and the desired conditions at any given time.
The governor has software that compares the desired engine speed to the actual engine speed. The actual engine speed is determined through the primary speed/timing sensor and the secondary speed/timing sensor. If the desired engine speed is greater than the actual engine speed, the governor injects more fuel in order to increase engine speed.
Timing Considerations
Fuel injection timing is determined by the ECM after considering input from the following components:
- Engine coolant temperature sensor
- The sensor for the intake manifold air temperature
- The sensor for the intake manifold pressure
- Speed/timing sensors
- Speed demand input device
At start-up, the ECM determines the top center position of the number 1 cylinder from the secondary speed/timing sensor in the fuel rail pump. The ECM decides when fuel injection should occur relative to the top center position. The ECM optimizes engine performance by control of each of the electronic unit injectors so that the required amount of fuel is injected at the precise point of the engine's cycle. The electronic unit injectors are supplied high pressure fuel from the fuel rail. The ECM also provides the signal to the solenoid in the fuel rail pump. The solenoid in the fuel rail pump controls a valve in the fuel rail pump. This valve controls the pressure in the fuel rail. Fuel that is not required for the engine is diverted away from the fuel rail pump back to the fuel tank.
The ECM adjusts injection timing and fuel pressure for the best engine performance, the best fuel economy and the best control of exhaust emissions. The actual timing can be viewed with an electronic service tool. Also, the desired timing can be viewed with an electronic service tool.
Fuel Injection
The personality module inside the ECM sets certain limits on the amount of fuel that can be injected.
The Fuel Ratio Control Limit is a limit that is based on intake manifold air pressure and engine rpm. The FRC Limit is used to control the air/fuel ratio in order to control the exhaust emissions from the engine. When the ECM senses a higher intake manifold air pressure, the ECM increases the FRC Limit. A higher intake manifold air pressure indicates that there is more air in the cylinder. When the ECM increases the FRC Limit, the ECM allows more fuel into the cylinder.
The Rated Fuel Limit is a limit that is based on the power rating of the engine and on the engine rpm. The Rated Fuel Limit enables the engine power and torque outputs to conform to the power and torque curves of a specific engine model.
These limits are in the personality module and these limits cannot be changedby the operator.
Diagnostic Codes
When the ECM detects an electronic system fault, the ECM generates a diagnostic code. Also, the ECM logs the diagnostic code in order to indicate the time of the occurrence of the fault. The ECM also logs the number of occurrences of the fault. Diagnostic codes are provided in order to indicate that the ECM has detected an electrical fault or an electronic fault in the engine control system. In some cases, the engine performance can be affected when the condition that is causing the code exists.
If the operator indicates poor performance, the diagnostic code may indicate the cause of the fault. Use the display on the control panel or the electronic service tool to access the diagnostic codes. The fault should then be corrected.
Event Codes
Event Codes are used to indicate that the ECM has detected an abnormal engine operating condition. The ECM will log the occurrence of the event code. This does not indicate an electrical malfunction or an electronic malfunction. For example, if the temperature of the coolant in the engine is higher than the permitted limit, then the ECM will detect the condition. The ECM will then log an event code for the condition. The engine may be derated when an event code is active.
Programmable Parameters
Certain parameters that affect the engine operation may be changed with electronic service tools. The parameters are stored in the ECM, and the parameters are protected from unauthorized changes by passwords. These restricted parameters are System Configuration Parameters.
System Configuration Parameters are set at the factory. System Configuration Parameters affect emissions or power ratings within the engine. Factory passwords must be obtained and factory passwords must be used to change the System Configuration Parameters.
Passwords
System Configuration Parameters are protected by factory passwords. Factory passwords are calculated on a computer system that is available only to Caterpillar dealers. Since factory passwords contain alphabetic characters, only an electronic service tool may change System Configuration Parameters. System Configuration Parameters affect the power rating or the emissions.
Refer to Troubleshooting, "Programming Parameters" and Troubleshooting, "Factory Passwords".