General Description
GENERAL DESCRIPTION
The Multipoint Fuel Injection (MFI) system is a system that supplies the optimum air-fuel mixture to the engine for all the various operating conditions through the use of the latest electronic technology.
With this system fuel, which is pressurized at a constant pressure, is injected into the intake air port of the cylinder head. The injection quantity of fuel is controlled by an intermittent injection system where the electro-magnetic injection valve (fuel injector) opens only for a short period of time, depending on the quantity of air required for one cycle of operation. In actual operation, the injection quantity is determined by the duration of an electric pulse applied to the fuel injector and this permits simple, yet highly precise metering of the fuel.
- Further, all the operating conditions of the engine are converted into electric signals, and this results in additional features of the system, such as large improved adaptability, easier addition of compensating element, etc.
The MFI system also has the following features:
- Reduced emission of harmful exhaust gases
- Reduced in fuel consumption
- Increased engine output
- Superior acceleration and deceleration
- Superior startability and warm-up performance in cold weather since compensation is made for coolant and intake air temperature.
The fuel system consists of:
- The delivery line supplies fuel from the fuel tank to the intake manifold and consists of a pump filter, fuel pump and fuel filter.
- The return line returns excess fuel to the fuel tank via the pressure regulator to maintain a constant level of fuel pressure.
- The evaporation line consists of a purge control solenoid valve, two-way valve and canister. Two fuel cut valves are additionally provided.
- The fuel tank is equipped with a jet pump so that the fuel level of both fuel tank chambers can always be kept equal.
- The evaporation line consists of a canister, vent control solenoid valve, roll over valve, fuel cut valve, fuel temperature sensor, fuel level sensor, fuel tank pressure sensor, pressure control solenoid valve and purge control solenoid valve.
FUEL STORAGE
The fuel storage system consists of a fuel tank, fill spout and filler cap.
FUEL INJECTION AND CONTROL
The injectors are solenoid operated valves designed to deliver fuel in an appropriate spray pattern to promote total fuel atomization in the intake air stream
The fuel injection control system consists of the ECM (Electronic Control Module) and all of the engine and operating condition sensors. Using the information from the sensors to determine the proper fuel amount and delivery time, the ECM varies the injectors "ON" time to adjust the amount of fuel delivered during each individual firing cycle.
For a more detailed description of the fuel injection system operation, refer to Computers and Control Systems.
FUEL DELIVERY AND RETURN
The fuel delivery system delivers fuel at a pressure and quantity high enough to allow the fuel regulator to maintain a constant fuel pressure in the fuel delivery rail (in reference to the intake manifold pressure) under all driving conditions. A check valve in the fuel pump holds pressure in the system after engine shutdown to prevent vapor lock and to ensure adequate pressure is available during warm engine re-start conditions.
The fuel delivery components consist of fuel supply lines, a high pressure fuel pump (mounted in the fuel tank), a fuel filter assembly and a fuel pressure regulator.
The fuel return system recovers excess fuel vented by the fuel pressure regulator (mounted on the fuel rail) and returns it to the fuel tank. The fuel return line is low pressure and returns directly to the fuel tank. The fuel return system consist of lines and couplings
FUEL VAPOR RECOVERY
The fuel vapor recovery system provides a route for the recovery of fuel vapors (from the fuel tank) either for storage in the charcoal canister, or for evacuation through the purge control system. The vapor recovery system also consists of lines and couplings. Additionally contained in the vapor recovery system are two components, an overfill limiter and a fuel check valve. These components function as evaporative emissions control devices and are therefore covered in detail in Emission Control Systems.