Electronic Fuel Injection (EFI) System - General Information

All vehicles covered in this Manual are equipped with the programmed fuel injection system (PGM-FI), which can be functionally divided into three main subsystems: the air intake system, the electronic control system, and the fuel supply system. The system operation is controlled by the PCM, which generates the necessary commands based on data received from information sensors (engine coolant temperature, throttle position [TPS], manifold absolute pressure [MAP], etc.). Based on the analysis of information received from the sensors, the PCM determines the optimal air-fuel mixture at the given moment.

The operation of the injection system closely interacts with the operation of the exhaust emission control system, for more detailed information on which refer to the Engine Control section.
Air Intake System
The system consists of the air cleaner, air ducts, throttle body, idle air control (IAC) valve and intake manifold. The intake manifold of both 4-cylinder and V6 engines consists of two sections: the lower (intake manifold proper) and the upper (surge chamber). Removal and installation procedures for both sections are described in the Engine section.

The throttle body has a single-bore, cross-flow design. The lower part of the throttle body is heated by engine coolant to prevent icing in cold weather. The idle speed adjusting screw is located on top of the throttle body. The throttle position sensor (TPS) is connected to the throttle shaft and monitors the degree of its opening.

At engine idle, the air-fuel mixture is controlled by the idle air control system (IAC), which includes the PCM, the engine coolant temperature (ECT) sensor, the IAC valve and a set of information sensors (intake air temperature [IAT] sensor, throttle position [TPS] sensor, manifold absolute pressure [MAP] sensor, etc.); refer also to the Engine Control section. The PCM controls the operation of the IAC valve based on the current engine load (operation of the air conditioning, power steering, coolant temperature, etc.). The valve regulates the flow of air entering the intake manifold through the throttle body. When generating commands to actuate the IAC valve, the PCM relies on data from various information sensors that determine the current vehicle speed, coolant temperature, air conditioning status (on/off), power steering usage, etc. To avoid instability of idle speed during engine start, the IAC valve opens while the crankshaft is cranking, immediately after the engine starts, in order to supply additional airflow into the intake manifold.
Electronic Control System
The composition and operating principle of the electronic control system and the PCM are described in detail in the Engine Control section.
Fuel Supply System
The fuel supply system components include: electric fuel pump, fuel pressure regulator, fuel injectors, fuel pulsation damper, fuel line and the main fuel system relay.

The electric fuel pump is located inside the fuel tank. The pump draws fuel from the tank through the strainer element, then pumps it through the additional fuel filter and supplies it to the fuel injectors. A relief valve is also provided to prevent excessive fuel pressure buildup in case of a blockage in the fuel passage.

The fuel pressure regulator maintains a constant fuel supply pressure to the injectors. Excess fuel is returned to the fuel tank through the return line.

The injectors are solenoid-operated constant-stroke valves. The main components of the injector are: the control solenoid, the plunger and the needle valve. All these parts are housed in a common body. When current flows through the solenoid coil, the needle valve partially opens, fuel under pressure fills the injector body cavity and is sprayed through its nozzle into the combustion chamber of the corresponding cylinder. The amount of injected fuel is determined by the duration of valve opening, i.e., the duration of voltage applied to the solenoid coil. To limit the current flowing through the injectors, resistors are included in the wiring circuits of the injectors.

The PCM controls the injector on-time. Base valve opening times for various combinations of input parameters (engine speed and intake air volume) are stored in the module memory. The necessary information is received by the module in the form of signals from various engine sensors.

The main fuel injection system relay is installed on the left or right side in front of the windshield under the cowl panel and consists of two operating elements: one is the PCM and fuel injector relay, and the second is the fuel pump relay.