Fuel injection system — general information

Central fuel injection (CFI)

The central fuel injection system is modular, providing pulsating injection from a point source. In accordance with the engine stroke, fuel is atomized into the incoming air stream by a single-coil injector installed in the intake manifold throttle body.

Fuel is supplied from the gas tank due to low pressure, as well as an electric pump mounted in the tank, the fuel is filtered and fed into the charging cavity, from where to the regulator, where the pressure is maintained at a certain level of 1 atm. (14.5 psi).

The single injector nozzle is mounted vertically above the throttle valves and comes with a fuel pressure regulator. Excess fuel pumped into the engine by the pump is returned to the gas tank through steel return pipes.

The fuel injection unit consists of five separate elements that perform the function of spraying fuel and air. The throttle body is bolted to a conventional carburetor mounting flange on the intake manifold; it includes the air control system, fuel injector nozzle, fuel pressure regulator, fuel pressure diagnostic valve, cold engine speed and throttle position sensors.

Airflow into the engine is controlled by a single throttle valve mounted in a two-piece die-cast aluminum housing called the throttle body. The configuration of the throttle valve is exactly the same as the throttle valves in a convection carburetor: it is activated by the same pedal and cable system.

The fuel injector nozzles are mounted vertically above the throttle valve and are an electromechanical device that atomizes and doses the amount of fuel entering the engine.


The nozzle valve consists of a ball driven by a solenoid and a seat.

A pilot electrical signal supplied by the EEC electronics energizes the solenoid causing the ball to rise off the seat and allowing fuel to flow through the valve.

Since the hole in the injector is of constant section and the fuel consumption is also constant, the amount of fuel that enters the engine is controlled by the time the solenoid is excited by the electrical signal.

The pressure regulator is made integral with the main body of the fuel injection device and is located near the rear surface of the air inlet. It is located in such a way as to neutralize the effect of fuel droplets coming from the make-up pipeline. The regulator device is insensitive to "back pressure in the pipelines for returning fuel to the tank.

Another function of the pressure regulator is to maintain the pressure of the injected fuel at the moment of idling of the fuel pump. In this case, the regulator acts as a check valve and keeps the fuel in the space between itself and the pump.

A constant level of fuel pressure after the engine is turned off prevents the formation of gasoline vapors and allows the engine to be immediately restarted and also ensures its stable idling. The fuel pressure at the injector nozzles is kept constant at 14.5 psi².

The throttle actuator maintains the idle speed by adjusting the throttle lever position to the desired airflow to provide the desired engine speed under all conditions from a cold engine idling to a hot engine at normal operating temperature. Idle switch (ITS) determines the moment of contact of the throttle lever with the activator and gives a signal to determine the number of engine revolutions. The DC motor increases or decreases the linear speed of the shaft through the gear mechanism. The direction of rotation is given by the polarity of the applied voltage. Throttle position sensor (not adjustable) mounted on the throttle shaft on the coil side of the fuel injection unit and is used to provide a voltage drop in proportion to the change in throttle position. The TP sensor is used by the computer (EEC) to determine the nature of the action (close the throttle, open the throttle partially, open the throttle fully) when choosing the correct composition of the mixture of fuel, spark and EGR at any speed and load conditions of the engine.

Electronic fuel injection system (EFI)

Electronic fuel injection system (EFI) used on 1991 four-cylinder engines and all V6 engines. In the 3.0LV6 engine, fuel is metered into the intake air stream in accordance with the engine's demand through six injectors mounted on the intake manifold. According to the energy supply, the nozzles are divided into two groups of three pieces each. Each group is activated once per revolution of the crankshaft. In 3.8LV6 engines, fuel is injected into each inlet at the same time in a sequence of three, injectors 1, 2 and 4 fire simultaneously, then 3, 5 and 6, following the ignition order of the engine itself and, accordingly, its fuel demand. All six injectors are mounted on the intake manifold.

In both systems, the on-board computer for electronic engine control (EEC - IV) receives impulses from various engine sensors and, on this basis, calculates the required amount of fuel supply to maintain the desired composition of the air-fuel mixture during the entire operation of the engine. After that, the computer issues a command for the consumption of an approximate amount of fuel to the fuel injectors. Injector connection time ("included" or "open") controlled by the EEC computer. Air entering the engine. evaluated by speed, pressure, temperature sensors.

The values given by these sensors are processed by the EEC - IV computer. The computer determines the opening time of the nozzle opening and issues a command to the nozzle to measure the exact amount of fuel.

The EEC-IV engine control system also detects and compensates for vehicle wear, accidental changes, and changes due to different altitude positions.

The fuel supply system is the same for both designs: an electric pump built into the tank pumps fuel under pressure through a system of metal and plastic pipes, as well as an internal fuel filter tank to the fuel injection manifold. The fuel injection manifold includes electric fuel injectors mounted above each inlet. Under the influence of an electrical impulse, the nozzles eject a strictly measured portion of fuel into the incoming air stream.

The pressure regulator maintains a constant level of pressure across all nozzles of the injectors. The regulator is produced together with fuel injectors, located below them. Excess fuel passes through the regulator and returns to the gas tank through the return lines.