Fuel Injection Control System
MFI Input/Output Signal Line:
PURPOSE
The Multiport Fuel Injection (MFI) System controls the amount of fuel the engine receives based on various system sensor inputs.
OPERATION
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 basic 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 crankshaft position sensor and the mass air flow sensor.
Injection Increase/Decrease Compensation
The amount of fuel injection is compensated to improve engine performance under various operating conditions as listed below.
< Fuel increase >
- During warm-up
- When starting the engine
- During acceleration
- Hot-engine operation
> Fuel decrease <
- During deceleration
Fuel Shut-Off
Fuel flow to all cylinders is stopped during deceleration or high speed vehicle operation.
Closed Loop System Operation:
Closed Loop / Mixture Ratio Feedback Operation
The mixture ratio feedback system is used for precise control of 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.
Open Loop Operation
Open loop control refers to the mode under which the ECM detects any of the following conditions and stops feedback control in order to maintain stabilized fuel combustion.
- Deceleration
- High-load, high-speed operation
- Engine idling
- Malfunction of heated oxygen sensor or its circuit
- Insufficient activation of heated oxygen sensor at low engine coolant temperature
- Engine starting
- Heated oxygen sensor high output voltage
Mixture Ratio Self-Learning
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 Engine Control Module (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 actual basic mixture ratio can differ from the theoretical target. This is due to manufacturing errors (e.g., mass air flow sensor hot wire) and changes during operation (injector clogging, etc.) of Electronic Concentrated Engine Control System (ECCS) parts which directly affect the mixture ratio.
The difference between the basic and theoretical mixture ratios is monitored in the system and computed in terms of "fuel injection duration" to automatically compensate for the difference between the two ratios.
Fuel Injection Timing Modes:
Fuel Injection Timing
Two types of fuel injection timing modes are used.
- simultaneous multi port fuel injection
- sequential multi port fuel injection
Simultaneous Multi Port Fuel Injection
Fuel is injected into all six cylinders simultaneously twice each engine cycle.
In other words, pulse signals of the same width are simultaneously transmitted from the Engine Control Module (ECM) to the six injectors two times for each engine cycle. This mode of fuel injection is used during engine starting.
Sequential Multi Port Fuel Injection
Fuel is injected into each cylinder during each engine cycle according to the firing order.