Multiport Fuel Injection (MFI) System
Multiport Fuel Injection input/output:
BASIC MULTIPORT FUEL INJECTION SYSTEM
The amount of fuel injected from the fuel injector, or the length of time the valve remains open, is determined by the Engine Control Module (ECM). The amount of fuel injected is a program value mapped in the ECM memory. In other words, the program value is preset by engine operating conditions determined by input signals (for engine speed and air intake) from both the camshaft position sensor and the mass air flow sensor.
FUEL INJECTION INCREASE/DECREASE
In addition, the amount of fuel injection is compensated for to improve engine performance under various operating conditions as listed below.
Fuel increase
1. During warm-up
2. When starting the engine
3. During acceleration
4. Hot-engine operation
Fuel decrease
1. During deceleration
Mixture Ratio Feedback Loop:
MIXTURE RATIO FEEDBACK CONTROL
The mixture ratio feedback system is designed to precisely control the mixture ratio to the stoichiometric point so that the three way catalyst can reduce CO, HC and NOx emissions. This system uses a heated oxygen sensor in the exhaust manifold to check the air-fuel ratio. The ECM adjusts the injection pulse width according to the sensor voltage so the mixture ratio will be within the range of the stoichiometric air-fuel ratio.
This stage refers to closed loop control. Open loop control refers to that under which the ECM detects any of the following conditions and feedback control stops in order to maintain stabilized fuel combustion.
1. Deceleration
2. High-load operation
3. Engine idling
4. Malfunction of heated oxygen sensor or its circuit
5. Insufficient activation of heated oxygen sensor at low engine coolant temperature.
6. Engine starting
MIXTURE RATIO SELF-LEARNING CONTROL
The mixture ratio feedback control system monitors the mixture ratio signal transmitted from the heated oxygen sensor. This feedback signal is then sent to the ECM to control the amount of fuel injection to provide a basic mixture ratio as close to the theoretical mixture ratio as possible. However, the basic mixture ratio is not necessarily controlled as originally designed. This is due to manufacturing errors (e.g., mass air flow sensor hot wire) and changes during operation (injector clogging, etc.) of ECCS parts which directly affect the mixture ratio.
Accordingly, a difference between the basic and theoretical mixture ratios is quantitatively monitored in this system. It is then computed in terms of "fuel injection duration" to automatically compensate for the difference between the two ratios.
Fuel Injection Timing:
FUEL INJECTION TIMING
Two types of fuel injection systems are used - simultaneous multiport fuel injection system and sequential multiport fuel injection system. In the former, fuel is injected into all cylinders simultaneously twice each engine cycle.
In other words, pulse signals of the same width are simultaneously transmitted from the ECM to the all injectors two times for each engine cycle.
In the sequential multi port fuel injection system, fuel is injected into each cylinder during each engine cycle according to the firing order.
When the engine is being started and/or if the fail-safe system (CPU of ECM) is operating, simultaneous multi port fuel injection system is used.
When the engine is running sequential multiport fuel injection system is used.
FUEL SHUT-OFF
Fuel to each cylinder is cut off during deceleration or operation of the engine at excessively high speeds.