ECI - System Fundamentals: Overview

87mitsubishi03

SUBJECT:

ECI SYSTEM FUNDAMENTALS
NO. STB-87-14-001

DATE February, 1987

MODEL All EFI vehicles
INTRODUCTION, SYSTEM DESCRIPTION, CLOSED & OPEN LOOP & INJECTOR TYPES INFORMATION

INTRODUCTION

The electronically-controlled fuel injection system in a Mitsubishi car is an example of advanced electronic technology applied to a popular consumer product. The system is made up of a computer, several sensors, and a set of injectors to meter fuel to the engine. Yet despite the system's complexity, it is actually as easy to diagnose as a mechanical system, and once the technician is acquainted with the characteristics of the system when it is functioning normally, he can successfully diagnose and correct even the most bewildering condition quickly and effectively. This bulletin describes the fuel injection systems used in current Mitsubishi cars and tells how they work. Also included is a diagnostic chart to help in determining when sensors are responsible for system malfunctions.

SYSTEM DESCRIPTION

Viewed in its simplest form, the electronic fuel injection system does nothing more than deliver to each cylinder the exact amount of fuel that is needed under a given set of conditions. Think for a moment of the conditions that would call for a change in the amount of fuel needed. Begin with the engine fully warmed up and idling. This can be called the "base line" because it represents the smallest fuel flow that the engine will need. Closed-throttle deceleration is an exception, because no fuel flow at all is desired at this time. Any other operating condition will call for more fuel. The sensors tell the computer how much additional fuel to order. They measure and report:

1. Air flow through the intake system
2. Coolant temperature
3. Intake air temperature
4. Throttle position
5. Exhaust gas composition (O2 Sensor)
6. Intake manifold pressure

Together, these sensors tell the computer to enrich the mixture so the engine can start and run when it is cold, or to provide an extra shot of fuel when the accelerator is depressed for acceleration. They tell it to lean-out the mixture as manifold pressure decreases or when the accelerator is released. In response to the O2 sensor, the computer changes the composition of the exhaust gases to minimize emissions. There are other sensors as well, such as the detonation sensor, but since these sensors do not control fuel flow they are not covered in this bulletin.
CLOSED-LOOP AND OPEN-LOOP OPERATION

The ECI system, like any other system that uses an oxygen sensor, has two modes of operation - "Closed Loop" and "Open Loop."

Closed Loop: In "Closed-Loop" mode, the air-fuel ratio is varied by the ECU based on information supplied by the Oxygen Sensor.

FIGURE 1:

Open Loop: In "Open Loop" mode, the air-fuel ratio is controlled by information programmed into the ECU at manufacture. Fig. 1 compares the two modes graphically. Both modes of operation are found in all MMSA ECI systems.
TYPES OF INJECTORS

Four different types of injectors are used on Mitsubishi cars. A single-point injector is used on the 1985 Galant. The 1986-87 Galant has a multi-point port injector system. Two types of twin-injector systems are used on all others.

Single Injector - 1985 Galant

The 1985 Galant uses a single injector in the throttle body. This injector is capable of delivering fuel in response to a variety of requirements from idle to maximum power.

FIGURE 2:

Twin Injectors - Before 1987

On pre-1987 cars with twin injectors, (Starion, Cordia/Tredia, and Mirage) the injectors pulse alternately
- first one and then the other (Fig, 2). Thus the total output of the two injectors is twice that of each one individually.

FIGURE 3:

Twin Injectors - 1987

On 1987 Starions and Mirages, twin injectors are also used, but on these cars two injectors of different flow rates are used. At idle speeds, fuel is injected through the smaller injector only. As load increases, fuel is injected by both the smaller injector and a larger second one. Fig. 3.

FIGURE 4:

Multi-Point Injectors

Cars with multi-point injection systems, such as the 1986 Galant, have one injector per cylinder. Thus the quantity of fuel delivered by each 1986 Galant injector is only approximately one-quarter as much as the single-point injector of the 1985 Galant. The pulse width is correspondingly less. Fig. 4 shows the injector pulse pattern graphically. Note that in the Galant system, the pulses are timed by ignition system firing pulses.