3126B Truck Engine Caterpillar

Illustration 1	g00292549
Electronic Control System Components (left side view) (1) Grommet for injector harness. (2) Injection actuation pressure sensor. (3) Air inlet heater. (4) Inlet air temperature sensor. (5) Atmospheric pressure sensor (if equipped). (6) Boost pressure sensor. (7) Engine harness connector "J2/P2". (8) Engine ground stud connection. (9) Vehicle harness connector "J1/P1". (10) Oil temperature sensor (if equipped). (11) Injection actuation pressure control valve. (12) Engine speed-timing sensors. (13) Coolant temperature sensor. (14) Oil pressure sensor (if equipped). (15) Electronic Control Module (ECM).

Illustration 2	g00292594
Electronic Control System Components (top view) (1) Grommet for injector harness. (2) Injection actuation pressure sensor. (3) Air inlet heater. (4) Inlet air temperature sensor. (5) Atmospheric pressure sensor (if equipped). (6) Boost pressure sensor. (8) Engine ground stud connection. (11) Injection actuation pressure control valve. (16) Relay of air inlet heater.

The electronic control system is integrally designed into the engine's fuel system and the engine's air inlet and exhaust system in order to electronically control the fuel delivery and the injection timing. The electronic control system provides increased timing control and fuel air ratio control in comparison to conventional mechanical engines. Injection timing is achieved by the precise control of the injector firing time. Engine rpm is controlled by adjusting the injection duration. The Electronic Control Module (ECM) energizes the unit injector solenoids in order to start the injection of fuel. Also, the Electronic Control Module (ECM) de-energizes the unit injector solenoids in order to stop the injection of fuel.

Refer to Systems Operation/Testing And Adjusting, "HEUI Injector Operation" for a complete explanation of the fuel injection process.

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

• pulse width

The variation of the signal is in response to a change in some specific system of the vehicle. Some specific examples of an input component are the engine speed-timing sensors, the coolant temperature sensor, and the cruise control switches. The ECM interprets the signal from the input component as information about the condition, environment, or operation of the vehicle.

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. The output component can use that electrical energy in order to provide information.

As an example, a moving solenoid plunger will perform work. By performing work, the component has functioned in order to regulate the vehicle.

As an example, a dash panel light or an alarm will provide information to the operator of the vehicle.

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