Fuel Delivery and Air Induction: Description and Operation
GENERAL- 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 improved adaptability, easier addition of compensating element, etc. The MFI system also has the following features:
1) Reduced emission of harmful exhaust gases.
2) Reduced fuel consumption.
3) Increased engine output.
4) Superior acceleration and deceleration.
5) Superior startability and warm-up performance in cold weather since compensation is made for coolant and intake air temperature.
The ECM receives signals sent from various sensors and switches to judge the engine operating condition and emits output signals to provide the optimum control and/or functioning of various systems.
Major items governed by the ECM are as follows:
- Fuel injection control
- Ignition system control
- By-pass air control (idle speed control)
- EGR control
- Canister purge control
- Radiator fan control
- Engine torque control
- A/C system control
- Fuel pump control
- Self-diagnosis function
FUEL PUMP CONTROL
- The ECM receives an input signal emitted from the crankshaft position sensor and ignition switch, and turns the fuel pump relay ON or OFF to control fuel pump operation.
To improve safety, the fuel pump will stop if the engine stalls with the ignition switch ON.
- When the fuel pump operating voltage is maintained at a constant level, the fuel pump also operates at a constant speed regardless of engine rpm. In the low engine speed range, much more fuel is discharged from the fuel pump than the amount of fuel injected from the fuel injectors. At this point, evaporation gases are produced inside the fuel tank. To decrease fuel discharged from the fuel pump when fuel consumption is reduced in the low engine speed range, the fuel pump modulator and resistor monitor are adopted to control the fuel pump.
FUEL PUMP MODULATOR OPERATION
- The fuel pump modulator changes fuel pump rotation in response to an ON/OFF signal sent from the ECM.
- In the low engine speed range, a signal sent from the ECM turns OFF the modulator. Power will then be supplied to the fuel pump via resistor. The fuel pump will now operate at low speeds.
- In high or intermediate engine speed range, a signal sent from the ECM turns ON the modulator. At this point, power is directly supplied to the fuel pump, bypassing the resistor, thus operating the fuel pump at high (normal) speeds.