3126B TRUCK ENGINE FOR FMTV MILITARY AP Caterpillar

P-1.0 3126B HEUI Electronic System Overview

Usage:

System Operation

The 3126B HEUI Truck Engines use a Hydraulic Electronic Unit Injector fuel system. The injection pump, fuel lines and nozzles required for fuel injection in mechanical Caterpillar engines have been replaced with a hydraulic electronic unit injector in each cylinder. Some mechanical drive components, cam lobes, lifter, push rod, and rocker arms required for fuel injection in mechanical or Electronic Unit Injector Caterpillar engines have been replaced with a high pressure oil system.

A solenoid on each injector controls the amount of fuel delivered by the injector. A gear-driven axial piston pump raises the normal engine operating oil pressure to injector actuation pressure levels required by the injectors. An Engine Control Module (ECM) sends a signal to the injection actuation pressure control valve to control injection pressure, and another signal to each injector solenoid to inject fuel.

Electronic Controls

The 3126B HEUI Truck Engines electronic system consists of the Engine Control Module (ECM), Engine Sensors, Injection Actuation Pressure Control Valve, and Vehicle Interface. The ECM is the computer which controls the 3126B HEUI engine. The Personality Module in the ECM contains the software which controls how the ECM behaves (the personality module stores the operating maps that define power rating, torque curves, rpm, etc).

Engine Governor

The Electronic Control system on the 3126B HEUI engine serves as the engine governor. The Electronic Control system determines when and how much fuel to deliver to the cylinders, as well as injection pressure based on the actual and desired conditions at any given time during starting and operation.

Basic Governor

The basic governor operation considers the desired and actual conditions, and then takes action to best accommodate the desired conditions.

The desired conditions are typically the position of the accelerator pedal, desired vehicle speed when in cruise control, or desired engine rpm when in PTO control. The actual conditions are based on current operating conditions such as coolant temperature, load conditions, etc.

Timing Considerations

Once the ECM has determined how much fuel is required, it must next determine when to inject the fuel. Injection timing is determined by the ECM after considering input from the coolant temperature sensor, intake manifold air temperature sensor, and boost pressure sensor.

The ECM knows the cylinder position for timing because of the signal from the Engine Speed/Timing Sensors. The ECM adjusts timing for best engine performance, fuel economy and white smoke control. Actual and Desired Timing cannot be viewed with an Electronic Service Tool.

The ECM knows where top center on cylinder #1 is from the signal provided by the engine Speed/Timing Sensors. The ECM decides when injection should occur relative to top center and provides the signal to the injector at the desired time.

Fuel Injection

The ECM controls the amount of fuel injected by varying signals to the injectors. The injectors will pump fuel only if the injector solenoid is energized. The ECM sends a high voltage signal to energize the solenoid. The energized solenoid lifts the poppet off its seat, closing the oil path to drain and opening the inlet for the high pressure oil. The high pressure oil enters the injector and acts on an intensifier piston, increasing the pressure and injecting fuel. By controlling the timing and duration of the high voltage signal, the ECM can control injection timing and the amount of fuel injected.

The ECM also controls the pressure of the fuel injected into the cylinder by controlling the Injection actuation pressure control valve. The injection actuation pressure control valve is a dump valve closely controlling the output pressure of the high pressure oil pump.

The Personality Module inside the ECM sets certain limits on the amount of fuel that can be injected. FRC Fuel Limit is a limit based on boost pressure to control the air/fuel ratio for emissions control. When the ECM senses a higher boost pressure (more air into cylinder), it increases the FRC Fuel Limit (allows more fuel into cylinder).

Rated Fuel Limit is a limit based on the power rating of the engine and rpm. It is similar to the rack stops and torque spring on a mechanically governed engine. It provides power and torque curves for a specific engine family and rating. All of these limits are determined at the factory in the Personality Module and cannot be changed in the field. Injection timing depends on engine rpm, load and other operating factors.

Injection Actuation Pressure System

The ECM controls fuel injection by controlling oil. The pressure of the oil in the high pressure oil manifold is controlled by the ECM through control of the injection actuation pressure control valve. The injection actuation pressure control valve (dump valve) controls the high pressure pump outlet pressure by dumping excess flow back to the oil sump.

The ECM monitors the pressure in the high pressure manifold through the injection actuation pressure sensor. The injection actuation pressure sensor is located in the top of the manifold on the left side of the engine. The injection actuation pressure sensor signal is compared by the ECM to the desired injection actuation pressure. The ECM determines the desired injection actuation pressure based on several inputs and changes the position of the injection actuation pressure control valve to adjust the oil pressure in the high pressure manifold.

High pressure oil is routed from the pump to the high pressure manifold through a steel tube. From the manifold the oil is routed to each injector through the high pressure oil manifold. All injectors have a constant supply of oil while the engine is running. Cutting out an injector disables the electrical signal to the injector solenoid, but does not interrupt the oil flow to the injector.

Customer Parameters Affect on Engine Governing

A unique feature of Electronic Engines is Customer Specified Parameters. These parameters allow the truck owner to instruct the ECM how to fine tune the engine operation to accommodate the typical usage of the vehicle, and to match the power train of the vehicle. Many of the Customer Parameters provide additional restrictions on the "Required Action" the ECM will take in response to the drivers' input.

Some parameters are intended to notify the driver of potential engine damage (Engine Monitoring Parameters). Some parameters enhance fuel economy (Vehicle Speed, Cruise Control, Engine/Gear Limits and Idle Shutdown Parameters). Other parameters are provided to enhance the engine installation or provide engine operation information to the truck owner.

Engine Monitoring

Caterpillar provides a factory installed Engine Monitoring system. The Caterpillar Engine Monitoring system monitors engine coolant temperature, and coolant level (optional). The coolant temperature sensor is standard on all engines.

Caterpillar Engine Monitoring can be programmed to four different modes (OFF, WARNING, DERATE, or SHUTDOWN). Some configurations do not allow the SHUTDOWN option to be selected. The Coolant Temperature Sensor will operate in the Engine Monitoring Mode selected.

Caterpillar Engine Monitoring OFF Operation

If Caterpillar Engine Monitoring is programmed to OFF, the control system ignores the coolant temperature sensor if conditions are exceeded which could cause the ECM to take Engine Monitoring action. The engine still uses the Coolant Temperature sensor for normal engine operation, such as for Cold Mode operation.

Caterpillar Engine Monitoring WARNING Operation

If the system is programmed to WARNING, the ECM causes the Check Engine/Service Engine Soon Lamp to Flash (because of the Active Diagnostic Code) to indicate a problem has been detected by the Engine Monitoring System. The diagnostic code is logged. No further ECM or engine action occurs if the ECM is programmed to WARNING.

Caterpillar Engine Monitoring DERATE Operation

Figure 1 - Engine Monitoring Coolant Temperature Graph

Figure 2 - Engine Monitoring Coolant Temperature Graph for Emergency Vehicles

If the system is programmed to DERATE, the ECM begins by flashing the Check Engine/Service Engine Soon Lamp to indicate a problem has been detected by the Engine Monitoring System. The diagnostic code is logged. For high coolant temperature conditions, the ECM limits the maximum vehicle speed and reduces available power as shown in Figure 1 - Engine Monitoring Coolant Temperature Graph on page 10 and Figure 2 - Engine Monitoring Coolant Temperature Graph for Emergency Vehicles on page 10.

This derating of usual engine performance is provided to influence the drivers' attention so action can be taken to avoid engine damage. The two graphs show the temperature derate trip points for the 3126B engines, and a rating for special applications.

Caterpillar Engine Monitoring SHUTDOWN Operation

If the system is programmed to SHUTDOWN the ECM takes all the action indicated for the DERATE mode and will eventually shut down the engine under some conditions.

When Very High Coolant Temperature, Very Low Coolant Level, or Very Low Oil Pressure is detected, SHUTDOWN mode begins by flashing the Warning Lamp the same as for DERATE. SHUTDOWN Mode will eventually cause the engine to shut down if the conditions continue long enough, and are severe enough. Following an Engine Monitoring Shutdown, the engine can be restarted an unlimited number of times to allow the vehicle to be pulled off to the side of the road.

Other ECM Performance Functions

The ECM also provides enhanced control of the engine for vehicle functions such as engine exhaust braking. The diagram 3126B HEUI Sensor and Connector Locations on page 13 shows many of the OEM systems the ECM can monitor to provide enhanced vehicle performance, fuel economy and driver convenience.

Self-Diagnostics

The 3126B HEUI electronic system has some ability to diagnose itself. When a problem is detected, a diagnostic code is generated and the Check Engine/Service Engine Soon lamp may come ON. In most cases, the code is also stored in permanent memory (Logged) in the ECM.

When diagnostic codes occur, they are called Active. They indicate a problem of some kind currently exists. They should always be serviced first. If a truck has an Active Code, find the code in the front of this manual and proceed to the indicated page to diagnose the cause.

Diagnostic codes stored in memory are Logged. Since the problem may have been temporary or may have been repaired since the time it was logged, logged codes do not necessarily mean something needs to be repaired. They are instead meant to be an indicator of probable causes for intermittent problems.

Some of the codes require passwords to clear. Codes not requiring passwords to clear are automatically deleted from memory after 50 engine operating hours.

Diagnostic Codes Effect on Engine Performance

This manual contains a table listing all of the PID-FMI Diagnostic codes, along with the page number where details regarding the cause, performance affect, and troubleshooting of the code can be located.

The table in PA-12: Possible Performance Effect of Active Diagnostic Codes on page 46 lists all 3126B HEUI Diagnostic Codes, and whether each code may or may not affect engine performance.

The discussion on Engine Monitoring mentions the Check Engine/Service Engine Soon Lamp flashes when a specific condition exists. When the ECM detects the engine problem, it generates an Active Diagnostic Code and also Logs the code to indicate when, and if appropriate, how many times the problem occurs. There are two types of Diagnostic Codes, Fault Codes and Event Codes.

Diagnostic Fault Codes are provided to indicate an electrical or electronic problem has been detected by the ECM. In some cases the engine performance can be affected when the condition causing the code exists. More frequently, however, the driver cannot detect any difference in the engine performance.

If the driver indicates a performance problem occurs whenever the Check Engine/Service Engine Soon Lamp is flashing, one of the Diagnostic Codes may be the cause of the problem, and should be corrected.

If the driver does not indicate a problem with the engine performance and a Diagnostic Code is logged by the ECM, it indicates the ECM detected an abnormal condition, but it did not affect performance.

If this is the case, unless there are several occurrences of the specific diagnostic code is a very short period of time, or the ECM is indicating the problem exists at the present time, there is most likely nothing wrong with the electronic system, and nothing to repair.

Diagnostic Event Codes are provided to indicate an operational problem has been detected in the engine (or truck) by the ECM. This usually does not indicate an electronic malfunction. Event codes typically are not an indication of an electronic system problem.

Current Totals Stored In The ECM

The ECM maintains engine total data for the following parameters. This information can be viewed on an electronic service tool.

Total Time is engine running hours (it does not include time when the ECM is powered ON without the engine running).

Total Distance data requires a vehicle speed sensor connected to the ECM (the same sensor used for ECM vehicle speed). This is the total number of kilometers (miles) the engine has been operated.

Total PTO Time and Total PTO Fuel are logged when the PTO ON/OFF switch is ON and the engine is operated under load, with the vehicle speed below the programmed PTO Vehicle Speed Limit.

Total Idle Time and Total Idle Fuel can include time when the engine speed is set using the Cruise switches and the vehicle speed is within range of the Idle Vehicle Speed Limit Parameter, but the engine is not operating under load.

Maintenance Indicator Data

The ECM records the Lifetime Data Totals when a maintenance reset occurs for three levels of maintenance - Maintenance Indicator PM1, Maintenance Indicator PM2, and Maintenance Indicator Coolant Flush/Fill. The previous maintenance point is used by the ECM to calculate when the next maintenance is due.

The Maintenance Indicator feature is programmable to hours or distance. The PM1 maintenance is programmable to OFF, Automatic-Distance, Automatic-Hours, Manual-Distance, or Manual-Hours.

If PM1 is programmed to Automatic (Distance or Hours), the ECM calculates the next maintenance due by considering the vehicle operation history from the previous maintenance interval. If the vehicle has a history of poor fuel economy, the maintenance indicator will occur sooner than a vehicle with better fuel economy.

The ECM also uses the Engine Oil Capacity, with a larger capacity providing a longer maintenance interval. Engine Oil Capacity is programmed in liters (quarts). If the PM1 Maintenance Indicator is programmed to Manual, the owner can program in their own specific maintenance mileage or time interval. PM2 and Coolant Flush/Fill intervals are determined by the factory.

CAT ID

The Caterpillar Driver Information Display (CAT ID) is available to provide operating information to the driver about the engine such as engine rpm, coolant temperature, boost pressure, etc, as well as engine fault codes with the PID-FMI and a brief text description.

CAT ID will also allow changing/resetting of certain operating parameters if the ECM is programmed to access these parameters as well as PM1 Reset and Theft Deterrent.

The Theft Deterrent feature allows the driver to input a four character password to shut the engine down and/or prevent the engine from restarting until the four character password is successfully entered.

NOTE: For CAT ID to function properly a DEC97 or later Personality Module is required in the ECM. The CAT ID must also have the EPROM chip capable of supporting communication with 3126B HEUI engines, software version 1.3 or later. The version number is displayed initially on power up of CAT ID.

Programmable Parameters

Certain parameters that affect 3126B HEUI Truck Engine operation may be changed with electronic service tools. The parameters are stored in the ECM, and are protected from unauthorized changes by passwords. These parameters are either "System Configuration Parameters" or "Customer Parameters".

System Configuration Parameters are set at the factory and affect emissions or power ratings within a family of engines. Factory Passwords must be obtained and used to change System Configuration Parameters.

Customer Parameters are variable and can be used to affect cruise control, vehicle speed limits, progressive shifting, rpm/power ratings within the limits set by the factory, Caterpillar Engine Monitoring, and PTO operation. Customer Passwords are necessary to change Customer Specified Parameters.

Some parameters may affect engine operation in ways a driver does not expect. Without adequate training, these parameters may lead to power or performance complaints, even when the engine is performing to specification. Refer to P-3.0 Programming Parameters on page 30 for more details.

Passwords

"System Configuration Parameters" are protected by Factory Passwords. Factory passwords are calculated on a computer system available only to Caterpillar dealers. Since factory passwords contain alphabetic characters, only an ECAP or Caterpillar Electronic Technician may change System Configuration Parameters. System Configuration Parameters affect power family or emissions.

"Customer Parameters" are protected by Customer Passwords. The customer passwords are programmed by the customer. See Customer Specified Parameters on page 30 for information on when passwords are needed and how to obtain them.