3412C Engine Caterpillar

Illustration 1	g00795230
Right side view (1) Electronic control module (ECM) (2) Rack position sensor (3) Boost pressure sensor (4) Coolant temperature sensor (5) Engine oil pressure sensor (6) Atmospheric pressure sensor (7) Speed sensor (8) Speed sensor

Illustration 2	g00354014
View A-A (9) Fuel shutoff solenoid (10) Rack solenoid (BTM) (11) ATA data link

The electronic control system is designed into the engine's fuel system. The system is designed to electronically control the delivery of fuel and injection timing.

The engine uses the following three types of electronic components:

• input component

• control component

• output component

An input component is one that sends an electrical signal to the ECM of the system. The signal that is sent varies in either of the following ways:

• voltage

• frequency

The ECM interprets the signal from the input component as information about the condition, environment, or operation of the engine.

A control component (ECM) receives the input signals from the input components. Electronic circuits inside the control component evaluate the signals from the input components. These electronic circuits also supply electrical energy to the output components of the system. The electrical energy that is supplied to the output components is based on predetermined combinations of input signal values.

An output component is one that is operated by a control module. The output component receives electrical energy from the control group. The output component uses that electrical energy in one of two ways. The output component can use that electrical energy in order to perform work. As an example, a moving solenoid plunger will perform work. The output component can use that electrical energy in order to provide information. As an example, a dash panel light or an alarm will provide information to the operator of the engine.

These electronic components provide the ability to electronically control the engine operation. Engines with electronic controls offer the following advantages:

• improvement in performance

• improvement in fuel consumption

• reduction in emissions levels

Various sensors feed engine data to the ECM. These sensors modify the following functions:

• boost pressure

• engine oil pressure

• engine speed

• fuel rack position

• throttle position

• on/off ignition

The ECM processes the data. Then, the ECM sends electronic signals to the fuel injection solenoids. The fuel injection solenoids move the fuel rack. This will optimize the efficiency and the performance of the engine.

The electronic engine control system also has the following built-in functions:

• engine overspeed

• on board diagnostics

Data Link

A data link is used for the following items:

• communicate the information from the engine.

• communicate with Caterpillar service tools.

• calibrate the electronic engine control system.

• troubleshoot the electronic engine control system.

• program the electronic engine control system.

The electronic engine control system includes a Data Link. The Data Link communicates with other microprocessor based devices. These devices are compatible with SAE Recommended Practices J1708 and J1587. The Data Link can reduce the duplication of sensors by allowing the controls to share information.

The Data Link is used to communicate engine information to other electronic control systems. The Data Link can interface with Caterpillar service tools such as the Electronic Control Analyzer Programmer (ECAP).

The Data Link monitors engine information. The engine information that is available on the Data Link includes the following information:

• boost pressure

• engine identification

• engine speed

• oil pressure

• rack position

• status and diagnostic information

• throttle position

The Electronic Control Analyzer Programmer (ECAP) is used to program the customer specified parameters.

The ECAP is one method of programming the customer specified parameters that are selected by the customer. The tool plugs into the Data Link Connector. This allows the tool to communicate with the ECM. Also, the ECAP can be used to display the real time values of all the information that is available on the Data Link. This will help diagnose engine problems.

System Diagnostic Codes

Refer to Electronic Troubleshooting Guide for a complete explanation of the Diagnostic Codes.

Electronic Control Module (ECM) And Personality Module

Illustration 3	g00354015
ECM and personality module (1) Electronic Control Module (ECM) (2) Fuel outlet (3) Fuel inlet (4) Personality module

The 3412C Generator Set Engine uses an ECM microprocessor. The ECM is mounted on the top of the aftercooler housing. The ECM (1) and the Personality Module (4) are cooled by fuel. The fuel circulates through a manifold between two circuit boards in the control module. The fuel enters the control module from the fuel transfer pump. The fuel enters the control module through the fuel inlet (3). Then, the fuel exits the control module through the fuel outlet (2) .

The inputs and the outputs to the control module are designed to withstand the short circuits to the battery voltage without damage to the control. The electronic engine control system has the following features that are designed into the system.

• Resistance to radio frequency

• Resistance to electromagnetic interference

The system has passed tests for interference that is caused by two-way radios and by switching noise.

The ECM power supply provides electrical power to all engine mounted sensors and actuators. The following precautions have been designed into the ECM.

• Reverse voltage polarity protection

• Power system voltage swings or surges due to sudden alternator load

In addition to acting as a power supply, the ECM also monitors all sensor inputs. The ECM provides the correct outputs. Also, the ECM ensures the desired engine operation.

The memory of the ECM stores a selected factory rating and the memory of the ECM identifies a selected factory engine rating. The memory also contains a personality module identification code. This code is used to avoid unauthorized tampering or switching of personality modules and other pertinent manufacturing information.

The wiring harness provides communications to the following areas:

• various sensors

• data link connector

• engine connectors

The Personality Module is attached to the ECM. The Personality Module provides all of the instructions that are necessary for the ECM to function. The Personality Module contains the information for the engine performance and the certification of the engine. This information includes the information on the fuel ratio and the rack control maps for a particular ratings group.

The ECM is programmed to perform the following functions:

• diagnostic tests on all inputs

• diagnostic tests on all outputs

• separate a fault to a specific circuit.

Once a fault is detected, the fault can be displayed on a diagnostic lamp. The Diagnostic Code can be read by using a service tool (ECAP). A multimeter can be used to check most problems. Also, a multimeter can be used to troubleshoot most problems. The ECM records most of the diagnostic codes that are generated during operation of the engine. The recorded codes or the intermittent codes can be read by the ECAP.

Throttle Control Sensor

A Throttle Control Sensor is used to interface with the throttle. The output of the Throttle Control Sensor is a constant frequency Pulse Width Modulation (PWM) signal rather than an analog voltage. Refer to Pulse Width Modulation in the glossary. The PWM signal overcomes the serious errors that can result from analog signals. These errors occur from the following problems.

• leakage between pins

• contamination in the wiring harness

• contamination in the connectors

The engine returns to low idle if the PWM signal is invalid from a broken wire or a shorted wire.

Fuel Rack Controls

Illustration 4	g00354016
Cross section view of the rack housing (1) Shutoff solenoid (2) Rack solenoid (BTM) (3) Fuel rack servo

Illustration 5	g00354018
Cross section view of rack position sensor (4) Fuel rack (5) Rack position sensor (6) Shutoff override shaft and lever assembly (manual shutoff)

Illustration 6	g00354019
Cross section view of engine speed sensor (7) Flywheel starter gear (8) Engine speed sensor

Engine oil pressure is used to move the fuel rack. An electronically actuated rack solenoid (BTM) (2) controls a double acting hydraulic servo. The servo directs engine oil pressure to either side of a piston that is connected to the fuel rack. The oil pressure moves the piston. The piston moves the fuel rack.

The servo group is a gerotor type oil pump. The servo group increases the pressure of the engine oil that is supplied to the governor. The increased oil pressure allows a better regulation of engine speed during the rapid application or the removal of heavy loads on the engine.

The rack solenoid (BTM) (2) is installed in the side of the rack actuator housing on the fuel injection pump. The rack solenoid (BTM) (2) is controlled by the ECM. The lever of the rack solenoid (BTM) is engaged in a collar on the rack servo valve. The rack solenoid (BTM) is spring loaded toward the fuel off position. The rack solenoid (BTM) must receive a positive voltage in order to move to the fuel on position.

Rack position sensor (5) is located inside the rack actuator housing. The rack position sensor is attached to the fuel rack by a magnet. The rack position sensor is a linear potentiometer that provides accurate feedback information for the ECM.

In addition to the rack position data, the ECM receives data from other sensors that are located in the rack actuator housing. The engine speed sensor (8) is triggered by radial slots on the flywheel. Oil pressure, inlet air pressure, and the boost pressure sensors are mounted on the engine. These sensors are connected to the ECM. The ECM will limit engine speed and power output of the engine if low oil pressure occurs. When there is a change in boost and/or inlet air pressure, the control module adjusts the quantity of fuel or the timing of fuel that is delivered to the engine.

The ECM operates an energized to run type shutoff solenoid (1). The shutoff solenoid will apply an additional force on the fuel rack in order to move the rack to the fuel off position, if the rack solenoid (BTM) (2) is unable to move the fuel rack to the fuel off position. A manual shutoff (6) (shutoff override shaft and lever assembly) is provided. The manual shutoff control shaft is spring loaded to a neutral position.

If the shutoff solenoid fails to energize, the solenoid override may be used to move the shutoff lever away from the fuel rack servo (3). This will allow the rack solenoid (BTM) to move the fuel rack even though the shutoff solenoid is not energized.

The manual shutoff may be used to shut down the engine when the shutoff solenoid is energized and the power is maintained to the ECM. This method of shutdown is used in some troubleshooting procedures.

The mechanical fuel ratio control, the torque control group, and the various adjustment screws have been eliminated. The electronic control module performs all of these functions. The control module adjusts the engine power and the torque rise. The control module compensates for the operation of an engine that has plugged air cleaners or the control compensates in order to limit the amount of smoke.

The amount of fuel that is needed by the engine to maintain a desired rpm is determined by the ECM. The engine speed will decrease when an additional load is applied and the engine is operating at a desired speed. The signal from the engine speed sensor (8) to the ECM changes. The control module performs the following tasks:

• receives the signal and receives the data

• processes all of the data

• sends a positive voltage to the rack solenoid (BTM)

The rack solenoid (BTM) moves the valve in fuel rack servo (3). This will cause the fuel rack to move in the Fuel On direction. The increase in fuel to the engine will increase engine speed. This action will continue until the engine is again running at the desired speed or until the rack position has increased up to a rack position limit.

The engine speed will increase if the load on the engine decreases. The ECM receives the changed signal from the engine speed sensor (8). The ECM reduces the electrical signal that goes to the rack solenoid (BTM). The rack solenoid (BTM) moves the valve in the fuel rack servo (3). This will move the fuel rack in the Fuel Off direction. The decrease in fuel to the engine will decrease engine speed. This action will continue until the engine is again running at the desired speed.

The electronic engine control system allows the engine to be cranked. The electronic engine control system allows the engine to start. The throttle control is not needed. The ECM will automatically provide the engine with the correct amount of fuel that is required to start the engine. Since some oil pressure is required for the fuel rack servo to move the fuel rack, electronically controlled engines may require a slightly longer cranking time to start.

Governor Servo

Illustration 7	g00354021
Rack movement toward Full Fuel (1) Piston (2) Cylinder (3) Sleeve (4) Valve (5) Fuel rack (A) Oil inlet (B) Oil outlet (C) Oil passage (D) Oil passage

When the rack solenoid (BTM) is energized, the rack solenoid (BTM) moves valve (4) to the left. The valve opens oil outlet (B) and the valve closes oil passage (D). Pressure oil from oil inlet (A) pushes piston (1) and fuel rack (5) to the left. Oil behind the piston goes through oil passage (C). The oil travels along valve (4) and exits through oil outlet (B).

Illustration 8	g00354022
No rack movement (constant engine speed) (1) Piston. (2) Cylinder. (3) Sleeve. (4) Valve. (5) Fuel rack. (A) Oil inlet. (B) Oil outlet. (C) Oil passage. (D) Oil passage. (1) Piston (2) Cylinder (3) Sleeve (4) Valve (5) Fuel rack (A) Oil inlet (B) Oil outlet (C) Oil passage (D) Oil passage

When the desired engine speed is reached, the rack solenoid (BTM) holds valve (4) in a fixed position. Piston (1) moves to the left until both oil outlet (B) and oil passage (D) are blocked by valve (4). Oil is trapped in the chamber behind piston (1). This creates a hydraulic lock. The piston and the fuel rack movement is stopped.

Illustration 9	g00354023
Rack movement toward Fuel Off (1) Piston (2) Cylinder (3) Sleeve (4) Valve (5) Fuel rack (A) Oil inlet (B) Oil outlet (C) Oil passage (D) Oil passage

When the rack solenoid (BTM) is de-energized, spring force in the solenoid moves valve (4) to the right. The valve closes oil outlet (B) and opens oil passage (D). Pressure oil from oil inlet (A) is now on both sides of piston (1). There is more area on the left side of the piston than the right side of the piston. The force of the oil is also greater on the left side of the piston. The piston and the fuel rack (5) moves to the right.