Multiport Fuel Injection (MFI) System

Multiport Fuel Injection (MFI) System-Input/Output Signal Line:

PURPOSE
The Multiport Fuel Injection (MFI) System controls the amount of fuel injected from the fuel injector is determined by the Engine Control Module (ECM).

OPERATION
The ECM controls the length of time the valve remains open (injection pulse duration). The amount of fuel injected is a program value 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 (CMPS) and the Mass Air Flow Sensor (MAF).

Injector Duration
In addition, the amount of fuel injection is compensated for 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
- When selector lever is moved from "N" to "D"

Fuel decrease
- During deceleration
- During high engine speed operation

Closed Loop System Operation:

Mixture Ratio Feedback Control
Mixture ratio feedback system is used for precise control of the air-fuel ratio to the stoichiometric point. The three-way catalyst (CAT) can then better reduce CO, HC and NOx emissions. This system uses a heated oxygen sensor in the exhaust tube to monitor the air-fuel ratio. The ECM adjusts the injection pulse width according to the sensor voltage signal. This maintains the mixture ratio within the range of the stoichiometric (ideal air-fuel mixture). This stage is referred to as the closed loop control condition.

Open Loop Control
The open loop control condition refers to when the ECM detects any of the following conditions. Feedback control stops 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

Mixture Ratio Self-learning Control
The mixture ratio feedback control system monitors the mixture ratio signal transmitted from the Heated Oxygen Sensor (H2OS). This feedback signal is then sent to the ECM. The ECM controls the 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 differences (e.g., Mass Air Flow Sensor (MAF) hot film) and changes during operation (injector clogging, etc.) of Electronic Concentrated Control System (ECCS) parts which directly affect the mixture ratio.

Accordingly, a difference between the basic and theoretical mixture ratios is monitored in this system. This is then 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 are used-MFI and Sequential Multiport Fuel Injection (SFI).

In the simultaneous multiport fuel injection system, 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 ECM to the six injectors two times for each engine cycle.

In the sequential multiport 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 Central Processing Unit (CPU) is operating, simultaneous multiport 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 engine speed.