Multiport Fuel Injection (MPI) system
In the system under consideration, electrical pulses of a strictly limited duration are used to control fuel injection through injectors directly into the intake port of each of the engine combustion chambers. The moment and duration of opening of each of the injectors are controlled by the electronic control module (ECM) of the system. The ECM continuously monitors the operating parameters of the engine and, based on an analysis of the incoming information, determines the required volume of fuel injected into each of the intake ports. In parallel, the ECM also controls the settings of idle speed and ignition timing. The throttle body serves exclusively to control the supply of air to the fuel system. Due to the fact that each of the cylinders is equipped with its own injector, located in close proximity to the intake valve, this scheme provides the ability to very accurately control the composition of the air-fuel mixture.
Fuel is supplied to the injectors under constant pressure, the value of which exceeds the pressure in the intake manifold. The fuel pressure regulator maintains a constant pressure difference between the input and output sections of each of the injection injectors. The regulator is equipped with a shut-off valve, a membrane-type sensitive element and a loaded spring. The pressure difference is controlled by throttling the fuel in the gap between the shut-off valve and its seat. Excess fuel is diverted back to the fuel tank via the return line.
Since fuel is supplied to each of the injectors with 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.
The fuel pressure pulsation damper (if provided) serves to eliminate the wave formation that occurs in the fuel lines at the moments of opening and closing the injection injectors. The damper is equipped with an air and fuel chambers separated by a membrane, which actually dampens elastic oscillations in the fuel flow.
The amount of air supplied to the engine is determined by the position of the throttle valve and the crankshaft speed. The air flow sensor installed in the intake tract provides the control module with information on the basis of which the ECM determines the required duration of injector opening.
Unless otherwise specified by the nature of the task, always disconnect the negative battery cable before servicing any fuel system components. Always have a Class B fire extinguisher readily available.
Before removing components (injectors, fuel line, pressure regulator)/disconnecting fuel lines, do not forget to relieve pressure in the fuel system. Try to avoid fuel coming into contact with exposed areas of the body. The nipple connector to be disconnected should be wrapped with a rag to prevent splashing of fuel under residual pressure. Immediately collect spilled fuel with paper towels, a sufficient supply of which should always be on hand.
Fuel pump and fuel lines
Fuel is supplied from the gas tank to the injection system and its excess is returned back to the gas tank via two metal lines laid under the bottom of the car. The submersible electric fuel pump of the rotary type is located inside the gas tank and is combined into a single assembly with the fuel consumption sensor unit. At the outlet of the fuel pump there is a fuel filter that ensures the filtration of particles up to 20÷30 microns in size.
The fuel vapor return system returns fuel vapors back to the fuel tank through a separate return line.
The fuel pump continues to operate as long as the engine is running, i.e. as long as the ECM receives reference pulses from the electronic ignition system (see Chapter Engine electrical equipment). After 2÷3 seconds after the supply of reference pulses ceases, the pump stops.
When loosening the nipple connectors, use two wrenches to avoid unwanted and dangerous deformations of the fuel lines. Strictly follow the regulatory requirements for tightening forces of the connectors. Remember that the sealing rings of the nipple connections must be replaced without fail when joining the latter.
The article is reprinted from a web resource mitsubishiman.ru
Exhaust system
The exhaust system consists of an exhaust manifold(s) equipped with an oxygen sensor, a downpipe, a catalytic converter, and a muffler.
The catalytic converter is the main component of the exhaust gas toxicity reduction system. The monoblock converter can be used in combination with a three-function reduction converter (for more details, see Chapter Engine management systems).