Multiport Fuel Injection (MFI) System

INPUT/OUTPUT SIGNAL LINE

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 ECM. The basic amount of fuel injected is a program value mapped in the ECM memory. The program value is preset by engine operating conditions. These conditions are determined by input signals (for engine speed and air intake) from both the camshaft position sensor and the mass air flow sensor.

VARIOUS FUEL INJECTION INCREASE/DECREASE COMPENSATION
The amount of fuel injection is compensated for to improve engine performance. This will be made under various operating conditions as listed below.

1. During warm-up
2. When starting the engine
3. During acceleration
4. Hot-engine operation


1. During deceleration
2. During high-speed operation




MIXTURE RATIO FEEDBACK CONTROL
The mixture ratio feedback system is used for precise control of the mixture ratio to the stoichiometric point, This is to enable the three way catalyst to reduce CO, HC and NOx emissions. This system uses an 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. Therefore, the mixture ratio is kept within the range of the stoichiometric air- fuel ratio. This stage refers to the closed loop control condition. Under the open-loop control condition, the ECM detects any of the following conditions. Then, the ECM feedback control stops to maintain stabilized fuel combustion.
1. Deceleration
2. High-load, high-speed 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
7. Heated oxygen sensor high output voltage

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. This is to provide a basic mixture ratio as close to the stoichiometric 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 stoichiometric mixture ratios is 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
Two types of systems are used - sequential multiport fuel injection system and simultaneous multi port fuel injection system.

Sequential Multiport Fuel Injection System
Fuel is injected into each cylinder during each engine cycle according to the firing order. This system is used when the engine is running.
Simultaneous Multi Port Fuel Injection System
Fuel is injected simultaneously into all six cylinders twice each engine cycle. In other words, pulse signals of the same width are simultaneously transmitted from the ECM. The six injectors will then receive the signals two times for each engine cycle. This system is used when the engine is being started and/or if the fail-safe system (CPU) is operating.

FUEL SHUT-OFF
Fuel to each cylinder is cut off during deceleration or high-speed operation.