Central Fuel Injection (CFI)
The central fuel injection system is modular, providing pulsating injection from a point source. In accordance with the engine operating cycle, fuel is sprayed into the incoming air flow by a single-coil injector installed in the throttle body of the intake manifold.
Fuel is supplied from the gas tank by low pressure, as well as an electric pump mounted in the tank, the fuel is filtered and supplied to the charging cavity, from where it is supplied to the regulator, where the pressure is maintained at a certain level of 1 atm. (14.5 psi).
The single nozzle of the injector is mounted vertically above the throttle valves and is supplied complete with a fuel pressure regulator. Excess fuel pumped into the engine by the pump is returned to the gas tank through steel return lines.
The fuel injection unit consists of five separate elements that perform the function of atomizing fuel and air. The throttle body is fixed to the normal 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.
Air flow into the engine is controlled by a single throttle valve mounted in a two-piece cast aluminum housing called the throttle body. The throttle valve is configured exactly like the throttle valves in a conventional carburetor: it is operated 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 metered the volume of fuel entering the engine.
The injector valve consists of a ball driven by a solenoid and a seat.
An electrical signal from the EEC's electronic processor energizes the solenoid, causing the ball to rise above the seat and allowing fuel to flow through the valve.
Since the hole in the injector is of constant cross-section and the fuel consumption is also constant, the amount of fuel entering the engine is regulated by the excitation time of the solenoid by an 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 neck. It is located so as to neutralize the effect of fuel drops coming from the feed pipe. The regulator device is insensitive to the "back" pressure in the fuel return pipes to the tank.
Another function of the pressure regulator is to maintain the pressure of the fuel being pumped when the fuel pump is idling. In this case, the regulator acts as a check valve and holds the fuel in the space between itself and the pump.
Constant 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 operation at idle. The fuel pressure in the injector nozzles is maintained constant within 14.5 psi.
The throttle actuator maintains idle speed by adjusting the throttle lever position to the required air flow to provide the desired engine speed under all conditions, from a cold engine at idle to a hot engine at normal operating temperature. The idle speed switch (ITS) senses when the throttle lever contacts the actuator and signals the engine speed to be sensed. The DC motor increases or decreases the linear speed of the shaft through a gearbox mechanism. The direction of rotation is determined by the polarity of the applied voltage. The throttle position sensor (non-adjustable) is mounted on the throttle shaft on the coil side of the fuel injection unit and is used to provide a voltage drop proportional 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) in selecting the correct mixture of fuel, spark and EGR under all engine speed and load conditions.
Electronic Fuel Injection (EFI)
Electronic Fuel Injection (EFI) is used on 1991 four-cylinder engines and all V6 engines. In the 3.0LV6 engine, fuel is metered into the intake air flow according to engine demand through six injectors mounted on the intake manifold. In terms of power supply, the injectors are divided into two groups of three each. Each group is activated once per crankshaft revolution. In the 3.8LV6 engines, fuel is injected into each intake port simultaneously in a sequence of three: injectors 1, 2 and 4 are activated 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 of the 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 required composition of the air-fuel mixture during the entire engine operation. After that, the computer issues a command for the consumption of an approximate amount of fuel to the fuel injectors. The time of connection of the injectors ("on" or "open") is controlled by the EEC computer. The air entering the engine is assessed by speed, pressure, and temperature sensors.
The values given by these sensors are processed by the EEC-IV computer. The computer determines the opening time of the injector and issues a command to the injector to measure the exact amount of fuel.
The EEC-IV engine control system also detects and compensates for vehicle wear, random changes and changes due to altitude differences.
The fuel delivery system is the same for both designs: an electric pump mounted in the tank forces fuel under pressure through a system of metal and plastic tubes, as well as an internal fuel filter reservoir, to the fuel injection manifold. The fuel injection manifold includes electric fuel injectors mounted above each inlet. Under the influence of an electric pulse, the injectors eject a precisely measured portion of fuel into the incoming air flow.
The pressure regulator maintains a constant pressure level across all injector nozzles. The regulator is manufactured together with the fuel injectors and is located below them. Excess fuel passes through the regulator and returns to the fuel tank via return lines.