System Operation
The fuel system for this engine uses Hydraulic Electronic Unit Injectors (HEUI). The injection pump, the fuel lines and the nozzles that are used in mechanical engines have been replaced with an hydraulic electronic unit injector in each cylinder. A solenoid on each injector controls the amount of fuel that is delivered by the injector. High pressure engine oil is used to operate the injector. An Engine Control Module (ECM) sends a signal to the injection actuation pressure control valve in order to control injection pressure. Another electrical signal is sent to each injector solenoid in order to inject fuel into the cylinders.
Electronic Controls
The engine's electronic system consists of the ECM, the engine sensors, the fuel injection system, and the vehicle interface. The ECM is used to control the operation of the engine. The ECM flash file contains the software that is used to program the ECM. The flash file contains the operating maps that define the following characteristics of the engine:
- Horsepower
- Torque curves
- Engine speed (rpm)
Engine Governor
The ECM provides the functionality of the engine governor.
The ECM determines the timing, the duration and the pressure of injection. The amount of fuel that is delivered to the cylinders is precisely controlled by the ECM. This control is based on the actual conditions and the desired conditions at any given time during starting and operation of the engine.
An accelerator pedal position sensor is used to determine the desired engine speed. The ECM compares the desired engine speed to the actual engine speed. The actual engine speed is calculated from signals that are generated by the engine speed/timing sensors. If the desired engine speed is greater than the actual engine speed, the ECM adjusts the signal that is sent to the injectors and the fuel system's high pressure oil pump in order to reduce the engine speed. The ECM continuously monitors the engine for actual conditions in order to adjust for desired conditions.
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| Illustration 1 | g01120999 |
Typical example | |
The desired engine speed is typically determined by one of the following conditions:
- The position of the accelerator pedal
- The desired vehicle speed in cruise control
- The desired engine rpm in PTO control
Timing Considerations
The ECM determines the fuel injection timing. In addition to desired engine speed and actual engine speed, the following inputs are used by the ECM in order to calculate the engine timing:
- Coolant temperature
- Intake manifold air temperature
- Atmospheric pressure
- Boost pressure
The signal from the engine speed/timing sensor is used by the ECM to determine the orientation of the crankshaft. This signal is used by the ECM to calculate an output for the injector solenoids relative to the top center position of each piston. The injection signal is adjusted for optimum engine performance, for fuel economy, and for the control of white smoke. The injection signal is output to each injector solenoid at the optimum time.
Fuel Injection
The ECM controls the injection timing and injection duration by varying the output signals to the injectors. The injectors pump fuel into the cylinder only while the injector solenoid is energized. The ECM outputs a high voltage signal to the injector solenoid in order to energize the solenoid. Energizing the injector solenoid actuates a seated pin inside the injector. The pin is seated and the injection actuation pressure increases within the fuel injector body. The hydraulic force that is provided by the actuation pressure is used to move an intensifier piston in the body of the injector. The intensifier piston multiplies the hydraulic force that is transfered to the fuel. As the force of the pressurized fuel overcomes the spring tension that is used to seat the nozzle check, fuel injection occurs.
Precise control of the injection actuation pressure and of the injector solenoid allows the ECM to deliver fuel over a varied rate during a single injection. This strategy provides the engine with optimum fuel economy and with strictly controlled emissions.
The software that is used to control the ECM provides instructions for the amount of fuel that can be injected into the cylinder. The "FRC Fuel Limit" is a limit that is based on the boost pressure. The "FRC Fuel Limit" is used to control the air/fuel ratio for the control of emissions. When the ECM senses a higher boost pressure, the ECM increases the "FRC Fuel Limit". A higher boost pressure indicates that the density of air that is entering the cylinder is being increased. When the ECM increases the "FRC Fuel Limit", the ECM also adjusts the signals to the fuel system. This adjusts the delivery of fuel to the cylinders.
The "Rated Fuel Limit" is a limit that is based on the power rating of the engine and of 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" defines the power curves and the torque curves for a specific engine family and for a specific engine rating. All of these limits are determined at the factory. These limits are contained in the ECM software and these limits cannot be changed.
Injection Actuation Pressure Control System
The ECM controls injection actuation pressure by controlling the output current to the injection actuation pressure control valve (IAPCV). The IAPCV utilizes the movement of spool valves that are inside the high pressure oil pump to control pump outlet pressure. By adjusting flow of control oil to the spool valves, the IAPCV controls the injection actuation pressure that is provided to the injectors. This determines the pressure of the fuel that is injected into the cylinder by the injectors.
The injection actuation pressure sensor provides a signal to the ECM that represents the pressure of the oil that is in the high pressure oil manifold. The injection actuation pressure sensor's signal is compared by the ECM to the desired injection actuation pressure. The desired injection actuation pressure is a calculated value that is based on sensor inputs, on control maps, and on power demands of the engine. The difference between the actual pressure and the desired pressure is used by the ECM to calculate adjustments to the control current that is output to the injection actuation pressure control valve. The ECM provides continuous monitoring and precise control of the pressure that is in the high pressure oil manifold.
High pressure oil is routed from the high pressure oil pump to the high pressure manifold through a steel tube. From the manifold, the oil is routed into each injector. All injectors have a constant supply of oil while the engine is running. Disabling the electrical signal to the injector solenoid does not interrupt the flow of high pressure oil that is available to the fuel injector.
"Basic" Systems and "Full Feature" Systems
Some 3126B HEUI Truck Engines ((S/N: 7AS8SZ)) were manufactured with one of two different engine control modules that were available. Each ECM must use different ECM software. These systems are commonly referred to as "Basic" and "Full Feature". "Basic" systems are typically found in GM trucks and chassis, while "Full Feature" systems are found in other applications. The "Basic" system and the "Full Feature" system use different default values for several of the customer parameters that are common to both of the systems. The ECM flash file for a "Basic" system cannot be used with a "Full Feature" system. The reverse is true as well. The "Full Feature" ECM provides some features that are not available with the "Basic" ECM. Refer to Troubleshooting, "Programming Parameters" for more details.
Other 3126B Truck Engines ((S/N: 8YL8SZ)) use an ECM that defines the features of both systems through the use of unique software. A new ECM parameter is used in the ECM flash file that is used to define each system. The "Truck Manufacturer" parameter is used to define the functionality of the "Basic" system versus the "Full Feature" system. This ECM parameter is configured at the factory to select the correct defaults and options for any given application. If an ECM replacement is required, the "Truck Manufacturer" parameter must be programmed for the specific vehicle. The software will then configure the ECM with the correct settings for that application.
Cold Mode
Cold mode is activated when the sum of coolant temperature and the inlet manifold air temperature is below 18 °C (64 °F). When cold mode is active, the idle rpm speed ramps up to the default value of 1000 rpm unless another value has been programmed into the "Warm Up Mode Idle Speed" parameter. Cold mode remains active until any of the following conditions are met:
- The sum of coolant temperature and the inlet manifold air temperature warms to 18 °C (64 °F).
- The engine has been started for 12 minutes.
- The service brake is depressed.
- The clutch pedal is depressed.
- The automatic transmission is placed in gear.
Customer Parameters and Engine Speed Governing
Unique features with electronic engines are customer specified parameters. These parameters allow the vehicle owner to define characteristics of engine operation to the specific needs of the application. The configuration of these parameters allows the vehicle owner to specify some aspects of engine operation for the typical usage and for the power train of the vehicle.
Many of the customer parameters provide control of the actions that will be performed by the ECM in response to the driver's input. For example, the "PTO Top Engine Limit" is a limit that is used to control the maximum engine speed during PTO operation. The "PTO Top Engine Limit" feature instructs the ECM to suppress the signal to the fuel injectors at engine speeds above an engine rpm that has been predefined .
Some of the engine monitoring parameters are intended to notify the driver of potential engine damage. Some parameters can be used in order to enhance fuel economy (Vehicle Speed, Cruise Control, Engine/Gear Speed Limit Parameter and Idle Shutdown). Some of the parameters must be used in order to accommodate the installation of the engine into a vehicle. Other parameters are also used to provide operating information about the engine to the truck engine owner.
Engine Monitoring
This engine utilizes a factory installed engine monitoring system. The engine monitoring system monitors the following variables:
- Coolant temperature
- Inlet manifold air temperature
- Coolant level (option)
- Engine oil pressure (option)
The engine monitoring system can be programmed to four different modes. The four modes of programming are "OFF", "WARNING", "DERATE", and "SHUTDOWN". The ECM will react to engine conditions according to the mode that is selected.
Functions of the Engine Monitoring System
"OFF" Mode
This option is not applicable for OCT01 ECM software.
If the engine monitoring system is programmed to "OFF", the ECM will not flag high coolant temperature or high inlet manifold air temperature. The ECM will not initiate warnings, derates, or shutdowns. If an adverse engine condition warrants an action, the ECM will not take action.
The ECM continues to monitor the engine sensors for engine operation. Cold mode operation, control of the air inlet heater, and control of the cooling fan will remain functional.
"WARNING" Mode
If the engine monitoring system is programmed to "WARNING", the ECM illuminates a warning lamp in the case of an abnormal operating condition or active diagnostic code. The ECM will also flash the check engine lamp when a diagnostic code becomes active. The lamps are used to communicate an abnormal operating condition. The engine monitoring system illuminates the lamps in order to warn the operator. The ECM will log the diagnostic code, but no further action will be initiated.
"DERATE" Mode
If the engine monitoring system is programmed to "DERATE" the ECM begins to begin flashing the check engine lamp and the warning lamp. . Again, this is done in order to communicate the problem to the operator. The ECM logs the diagnostic code. For a high coolant temperature, the ECM will limit the maximum vehicle speed. The engine power rating is also reduced. Refer to Illustration 2 and Illustration 3.
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| Illustration 2 | g01121008 |
Coolant temperature bargraph Limited derate mode (10 percent per second) | |
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| Illustration 3 | g01121023 |
Coolant temperature bargraph for emergency vehicles Limited derate mode (10 percent per second) | |
The ECM will also respond to a low coolant level by limiting the maximum vehicle speed. The engine power rating is derated as well. Refer to Illustration 4.
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| Illustration 4 | g01121033 |
Graph for the coolant level Limited derate mode (10 percent per second) | |
The response to a very low oil pressure will also affect the vehicle speed and the engine power rating. Refer to Illustration 5.
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| Illustration 5 | g01121043 |
Graph for very low oil pressure | |
An engine derate is provided in order to protect the engine and/or the vehicle from specific abnormal conditions.
"SHUTDOWN" Operation
If the system is programmed to "SHUTDOWN", the ECM activates the actions of the "DERATE" mode. If the conditions deteriorate to predetermined levels, the ECM will initiate the engine shutdown.
The "SHUTDOWN" mode begins when any of the following conditions exist:
- "Very low oil pressure"
- "Very low coolant level"
- "Very high coolant temperature"
Note: The very low oil pressure is only available on "Full Feature" systems.
After the ECM has completed an engine shutdown for conditions that relate to engine monitoring, the ECM allows the engine to be restarted. If adverse conditions persist, engine monitoring will repeat the engine shutdown.
Other Functions of the Engine Monitoring System
The ECM also provides enhanced control of the engine for vehicle functions such as exhaust brake and PTO controls. Refer to Troubleshooting, "Customer Specified Parameters" for supplemental information that is related to other functions of the monitoring system.
Self-Diagnostics
The ECM has the ability to diagnose problems that relate to the engine's and to the vehicle's electronics. When an electrical problem is detected the ECM activates a diagnostic code. The ECM communicates this diagnostic information to the operator by illuminating a check engine/diagnostic lamp. The ECM also stores the information in permanent memory. An active diagnostic code indicates that an electrical problem has been detected by the ECM. The code will remain active while the problem is detected by the ECM.
Diagnostic codes that are stored in the ECM memory are referred to as logged diagnostic codes. A logged diagnostic code that is read from ECM memory does not necessarily indicate that something needs to be repaired. The problem may have been temporary, or the problem may have been repaired since the problem was logged. Logged diagnostic codes intended to provide historical information about electrical problems that have been detected by the ECM. A common use for this information is troubleshooting intermittent electrical problems.
Event codes are used to identify engine operating conditions that are outside the normal operating range. Event codes are not typically an indication of an electronic system problem. For example, an event code is logged into ECM memory if engine overspeed condition occurs.
Some of the logged codes require passwords to be cleared from ECM memory. Diagnostic codes that do not require passwords to be cleared from memory are automatically deleted after 50 hours of engine operation.
Engine Snapshot Data
When a diagnostic code becomes active, the ECM records the time of the occurrence in ECM memory. The ECM also records an engine snapshot prior to the occurrence and after the occurrence. The engine snapshot is a record of specific operating parameters. The ECM records data for ten seconds before the diagnostic code becomes active and for three seconds after the diagnostic code becomes active.
An engine snapshot can also be triggered from the cruise control set/resume switch. In order to trigger the engine snapshot from the cruise control set/resume switch, quickly toggle the switch to the SET position. Then, quickly toggle the switch to the RESUME position. Toggling the cruise control set/resume switch from the RESUME position to the SET position will also activate the feature.
Caterpillar Electronic Technician (ET) can also be used to activate an engine snapshot. The data from an engine snapshot can be retrieved with Cat ET as well.
Effect Of Diagnostic Codes on Engine Performance
Diagnostic Codes
Diagnostic codes are activated by the ECM in order to indicate that an electrical problem or an electronic problem has been detected by the ECM. Some of the problems that cause the codes may have an effect on engine performance while other problems that are detected may not have an effect. More frequently, the driver will not detect any difference in engine performance.
If the check engine lamp is flashing and a change in engine performance is apparent, the cause of the code may also be the cause of the change in engine performance. Troubleshoot active diagnostic codes prior to performing any other service on an engine. Be sure to check for the occurrence of logged diagnostic codes in ECM memory. This will provide information on problems that are intermittent or problems that occur only during specific operating conditions.
Event Codes
Event codes are used to identify abnormal operating conditions of the engine. Event codes seldom identify electrical problems or electronic problems with the engine. During the detection of an event, the ECM logs the code into memory.
The following codes are available for this engine:
- 84-00 Vehicle Overspeed Warning (41)
- 100-11 Very Low Oil Pressure (46)
- 110-11 Very High Coolant Temperature (61)
- 111-11 Very Low Coolant Level (62)
- 190-00 Engine Overspeed Warning (35)
The ECM uses an internal clock to time stamp the occurrence of an event code. This information is also stored in ECM memory.
ECM Lifetime Totals
The ECM records the total data in permanent memory for the following parameters:
Total Time (Engine Hours) - The total time is accumulated during the operational hours of the engine. The engine hours do not include the time when the ECM is powered and the engine is not running.
Total Distance - The distance data requires a vehicle speed sensor or an electronic vehicle speed source to be connected to the ECM. The same sensor must be used for the vehicle speed parameter. Distance can be displayed in miles or kilometers.
"PTO Time" and "PTO Fuel" - This is recorded when the PTO on/off switch is in the ON position and vehicle speed is within the range of the "PTO Vehicle Speed Limit" parameter.
"Idle Time" and "Idle Fuel" - Idle information is recorded only when the engine speed is set by using the cruise switches and the vehicle speed is within the range of the "Idle Vehicle Speed Limit" parameter.
Average Load Factor - This provides relative engine operating information. The average load factor is derived from the engine's "Total Maximum Fuel", "Idle Fuel", and "Fuel Consumption" data.
Total Fuel - This is the maximum amount of fuel that is consumed by the engine during operation.
Total Maximum Fuel - This is the amount of fuel that could have been consumed by the engine during operation.
Note: Fuel information can be displayed in US gallons or in liters.
This information can be viewed with Cat ET.
Other Information That is Stored in the ECM Memory
The "Fleet Trip Data" allows information that is related to engine operation to be recorded over specified intervals. These intervals are defined by the vehicle owner (July 1999 and newer ECM software). This data is stored in ECM memory. If power is removed from the ECM, the data is retained in memory with an internal battery backup.
Fleet Trip Data
The functionality for the fleet trip data includes a "Fleet Trip Segment", histograms, and custom data. The "Fleet Trip Segment" includes data for the following parameters:
- Time (engine hours)
- Driving time
- Distance
- Fuel
- Idle time
- Idle fuel
- PTO time
- PTO fuel
- Average load factor
- Average vehicle speed
- Idle time (percent)
- PTO time (percent)
- Overall fuel economy
- Driving fuel economy
- Average driving speed
- Maximum vehicle speed
- Maximum engine speed
- Start time
- End time
- Odometer (start)
- Odometer (end)
The "Fleet Trip Data" feature can be configured for three different histograms:
- Engine operation versus engine speed
- Vehicle speed versus time
- Engine speed and vehicle speed versus time
Cat ET can be used to calculate the averages of the parameters over time. Custom data is also available. Custom data allows the recording of engine parameters that are specified by the vehicle owner.
Maintenance of the fleet trip data can be performed by using any of the following tools:
- Cat ET
- Caterpillar Fleet Information Software (FIS)
- Caterpillar Driver Information Display (CAT ID)
- Caterpillar Messenger
Maintenance Indicator Data
The ECM records the current totals when a reset occurs for the following maintenance options:
- PM1
- PM2
- Cooling system clean/flush
The ECM uses the previous point of maintenance in order to calculate the time of the next scheduled maintenance.
The "Maintenance Indicator Mode" can be programmed to hours or to distance.
The "PM1" maintenance parameter can be programmable to "Off", to "Automatic Distance", to "Automatic Hours", to "Manual Distance", or to "Manual Hours".
If the "PM1" is programmed to the "Automatic" mode, the ECM calculates the next point of maintenance by considering the history of the vehicle's operation from the previous maintenance interval. If the vehicle has a history of poor fuel economy the "Maintenance Indicator" parameter will occur sooner than a vehicle with better fuel economy.
The ECM also uses the engine oil capacity to determine the maintenance interval. An engine oil capacity that is larger provides oil change intervals that are longer. The engine oil capacity is programmed into the ECM in liters or in quarts. If the "PM1" is programmed to the "Manual" mode, the owner can program the ECM with a unique maintenance interval.
The maintenance interval can also be programmed to the owner's specific interval that can be based on mileage or on time.
The interval for the "PM2" and the interval for the cooling system clean/flush are established by the factory.
Messenger
Caterpillar Messenger is available to provide engine operating information to the driver. The "Fleet Trip Data", and the "Maintenance Indicator" data can be viewed. However, the fleet trip histograms and the custom data cannot be viewed from the display.
Messenger provides the ability to enter an ID code for a driver in order to divide the "Fleet Trip Data" for two drivers. If the driver enters the information regarding the state of travel, the "Fleet Trip Data" can be tagged by the state of travel.
Messenger can be used in order to tag portions of the "Fleet Trip Data" into two ID codes. Messenger can also be used in order to tag portions of the "Fleet Trip Data" into the state of travel. The ID code and the information regarding the state of travel cannot be viewed from the display. Only the Caterpillar FIS can view this information. The ability to reset any of these parameters is dependent on customer parameters in the ECM.
Messenger will also display operating information such as engine rpm, coolant temperature, boost pressure, PTO parameters, etc.
Diagnostic data can also be viewed with Messenger. Engine diagnostic codes that use the PID-FMI format can be displayed. Messenger also displays a brief text description of the diagnostic codes that are active.
Another available feature on Messenger is the theft deterrent. The theft deterrent allows the driver to input a password prior to shutdown. The theft deterrent will prevent the engine from restarting until the password is successfully entered. Messenger must have the version of software that is capable of supporting this feature.
An "Auto-Enable" option is available for the theft deterrent. If this option is selected, the theft deterrent will automatically be activated when the engine is shut down. The driver must input the correct password in order to start the engine.
"Secure Idle" is another theft deterrent. This allows the driver to bring the engine to an idle condition. The driver then enters the password. The engine will remain at low idle until the password is re-entered. If the engine is shutdown, a password will be required to go above low idle after start-up.
Fleet Information Software (FIS) (JUL99 and Newer ECM Software)
The Caterpillar FIS is another method that can be used to review the trip information. The entire "Fleet Trip Segment", which includes the following elements of data can be accessed with the Caterpillar FIS:
- Histograms
- Custom data
- Information that is tagged by the ID code
- Information that is tagged by the state of travel
Maintenance Indicator information can also be accessed by using the Caterpillar FIS.
When the Caterpillar FIS downloads the information, the Caterpillar FIS also resets the ECM in order to prepare the ECM for the next trip. The information can be downloaded to a computer with the Caterpillar FIS, or the information can be downloaded to an Argo Mobile Data Tool. The Argo Mobile Data Tool is then connected to a computer in order to download the information.
Programmable Parameters
Certain parameters that affect the operation of the HEUI engine may be changed using Cat ET. These parameters are stored in the ECM and most of the parameters are password protected. These parameters are either system configuration parameters or customer parameters.
System configuration parameters are parameters that define the engine operation or the engine application. These parameters are set at the factory. System configuration parameters define the power rating and emissions levels. Factory passwords are required to change system configuration parameters. Factory passwords are available only to authorized Caterpillar Dealers.
Customer parameters are parameters that are available to the customer or to the vehicle manufacturer. Some of the customer parameters are configured to specifically define the application of the engine. Other customer passwords can be set by the owner in order to tailor the engine to the specific use by the customer. The following parameters are typical parameters that can be configured by the customer:
- Parameters that define cruise control functions
- Vehicle speed limits
- Parameters that define the progressive shifting
- Engine rpm settings
- Maintenance interval schedules
Customer passwords may be required to change customer specified parameters.
Some of the parameters may affect engine operation in an unusual way. A driver might not expect this type of effect. Without adequate training, these parameters may lead to power complaints or performance complaints even though the engine's performance is to the specification.
Refer to Troubleshooting, "Customer Specified Parameters".
Passwords
System configuration parameters specify the power rating, the family, and the emissions of an engine. These parameters are protected by factory passwords. Changing these parameters requires the use of factory passwords. Factory passwords are available only through authorized Caterpillar dealers. Cat ET must be used to change system configuration parameters.
Customer parameters are protected by customer passwords. The customer passwords are programmed by the customer. Factory passwords can be used to change customer passwords if customer passwords are lost.
Refer to Troubleshooting, "Customer Passwords" and Troubleshooting, "Factory Passwords".