The engines were designed for electronic control. The injection pump, the fuel lines and the nozzles that are used in mechanical engines have been replaced with an electronic unit injector in each cylinder. A solenoid on each injector controls the amount of fuel that is delivered by the injector. An Electronic Control Module (ECM) sends a signal to each injector solenoid in order to provide complete control of the engine.
The electronic system consists of the Electronic Control Module (ECM), the engine sensors, and the Machine Interface. The ECM is the computer. The personality module is the software for the computer. The personality module contains the operating maps. The operating maps define the following characteristics of the engine:
- Horsepower
- Torque curves
- Engine speed (rpm)
The electronic controls determine the 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 compares the desired engine speed to the actual engine speed. The actual engine speed is determined through the crankshaft position sensor. If the desired engine speed is greater than the actual engine speed, the governor injects more fuel in order to increase engine speed.
Once the governor has determined the amount of fuel that is required, the governor must determine the timing of the fuel injection. Fuel injection timing is determined by the ECM after considering input from the following components:
- Coolant temperature sensor
- Inlet air temperature sensor
- Atmospheric pressure sensor
- Turbocharger outlet pressure sensor
At start-up, the ECM determines the top center position of the number 1 cylinder from the camshaft position sensor's signal. After start-up, the ECM determines the top center position of the number 1 cylinder from the crankshaft position sensor. The ECM decides when fuel injection should occur relative to the top center position and the ECM provides the signal to the injector at the desired time. The ECM adjusts timing for the best engine performance, the best fuel economy and the best control of white smoke. Actual timing cannot be viewed with an electronic service tool. Also, desired timing cannot be viewed with an electronic service tool.
The ECM controls the amount of fuel that is injected by varying the signals to the injectors. The injectors will pump fuel only if the injector solenoid is energized. The ECM sends a high voltage signal to the solenoid. This high voltage signal energizes the solenoid. By controlling the timing and the duration of the high voltage signal, the ECM can control injection timing and the ECM can control the amount of fuel that is injected.
The personality module inside the ECM sets certain limits on the amount of fuel that can be injected. The FRC Limit is a limit that is based on the turbocharger outlet pressure. The FRC Limit is used to control the air/fuel ratio for control of emissions. When the ECM senses a higher turbocharger outlet pressure, the ECM increases the FRC Limit. A higher turbocharger outlet 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 engine rpm. The Rated Fuel Limit is similar to the rack stops and the torque spring on a mechanically governed engine. The Rated Fuel Limit provides the power curves and the torque curves for a specific engine family and a specific engine rating. All of these limits are determined at the factory. These limits are in the personality module and these limits cannot be changed.
Effect Of Diagnostic Codes On Engine Performance
When the ECM detects an engine problem, the ECM generates an active diagnostic code. Also, the ECM logs the diagnostic code in order to indicate the time of the problem's occurrence. The ECM also logs the number of occurrences of the problem. There are two types of diagnostic codes. There are fault codes and event codes.
Diagnostic fault codes are provided in order to indicate that an electrical problem or an electronic problem has been detected by the ECM. In some cases, the engine performance can be affected when the condition that is causing the code exists. More frequently, the operator cannot detect any difference in the engine performance.
If the operator indicates that a performance problem occurs, the diagnostic code may indicate the cause of the problem. Use the diagnostic enable switch to access the diagnostic codes. The problem should be corrected.
If the operator does not indicate a problem with the engine performance and a diagnostic code is logged by the ECM, the situation indicates that the ECM detected an abnormal condition, but the abnormal condition did not affect engine performance.
In this situation, the system has no faults except when either of the following conditions exist:
- There are several occurrences of the diagnostic code in a very short period of time.
- The ECM is indicating an active code at the present time.
Diagnostic event codes are used to indicate that some operational problem has been detected in the engine or in the machine by the ECM. This does not indicate an electronic malfunction.
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 parameters are System Configuration Parameters.
System Configuration Parameters are set at the factory. System Configuration Parameters affect emissions or power ratings within an engine family. Factory passwords must be obtained and factory passwords must be used to change the System Configuration Parameters.
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 family or emissions.
Refer to Troubleshooting, "Programming Parameters" and Troubleshooting, "Factory Passwords".