Multiport fuel injection system (MPI)
In the system under consideration, to control the injection of fuel through injectors directly into the intake port of each of the combustion chambers of the engine, electrical impulses of a clearly limited duration are used. The moment and duration of the opening time of each of the injectors is controlled by the electronic control module (ECM) systems. The ECM continuously monitors the engine's operating parameters and, based on the analysis of incoming information, determines the required amount of fuel injected into each of the intake ports. In parallel, the ECM also controls the idle speed and ignition timing settings. The throttle body serves solely to control the air supply to the air supply system. Due to the fact that each of the cylinders is equipped with its own injector located in the immediate vicinity of the intake valve, this scheme allows for very precise control of the composition of the air-fuel mixture.
Fuel enters the injectors under a constant pressure, the value of which exceeds the pressure in the intake manifold. The fuel pressure regulator maintains a constant pressure difference between the inlet and outlet sections of each of the injection injectors. The regulator is equipped with a check valve, a diaphragm type sensing element and a loaded spring. The pressure drop is controlled by throttling the fuel in the gap between the shut-off valve and its seat. Excess fuel is returned to the fuel tank through the return line.
Since fuel is supplied to each of the injectors at a constant pressure, the amount of fuel injected into the engine is determined solely by the duration of the injector opening, which is controlled by the ECM. The same module monitors the compliance of the valve timing and ignition phases.
Fuel pressure pulsation damper (if provided) serves to eliminate wave formation that occurs in petrol pipelines at the moments of opening and closing of injection injectors. The damper is equipped with air and fuel chambers separated by a membrane, which actually damps elastic vibrations in the fuel flow.
The amount of air supplied to the engine is determined by the position of the throttle valve and the speed of the crankshaft. An intake air flow sensor provides the control module with information from which the ECM determines how long the injectors need to open.
Unless otherwise required by the nature of the task being performed, be sure to disconnect the negative cable from the battery before you start servicing the components of the power system. Always have a class B fire extinguisher ready.
Before removing components (injectors, fuel line, pressure regulator) /disconnecting the fuel lines, do not forget to depressurize the fuel system. Try not to allow fuel to come into contact with exposed areas of the body. Wrap a rag around the union to be disconnected to prevent splashing of the fuel under residual pressure. Soak up spilled fuel immediately with paper towels, an adequate supply of which should always be on hand.
Fuel pump and fuel lines
The supply of fuel from the gas tank to the injection system and the return of its excess back to the gas tank is carried out through two metal lines laid under the bottom of the car. The rotary type submersible electric fuel pump is located inside the gas tank and is integrated into a single assembly with the fuel flow sensor unit. A fuel filter is provided at the outlet of the fuel pump, which provides filtering of particles up to 20 ÷ 30 microns in size.
The fuel vapor return system carries out the removal of fuel vapors back to the gas tank through a separate return line.
The fuel pump continues to function during the entire time the engine is running, i.e., while the ECM receives reference pulses from the electronic ignition system (see chapter Engine electrical equipment). After 2÷3 seconds after the interruption of the supply of reference pulses, the pump stops.
Use two wrenches when loosening the nipple connectors to avoid unwanted and dangerous deformation of the fuel lines. Strictly observe the regulatory requirements for tightening torques of connectors. Remember that the sealing rings of the fitting connections must be replaced without fail when the latter are joined.
Exhaust system
The exhaust system consists of an exhaust manifold equipped with an oxygen sensor (ov), downpipe, catalytic converter, and muffler.
The catalytic converter is the main component of the emission control system. The monoblock transmitter can be used in combination with a three-function reducing (see Chapter Engine management systems).