Hyundai Coupes/Sedans 1994-1998 Repair Guide

General Information


The fuel injection system used on Hyundai vehicles is classified as a Multi-port Fuel Injection (MFI) system. The basic function of the system is to control the air/fuel ratio, based on input signals from various engine sensors. The air/fuel ratio is controlled by varying the injector drive time (pulse width). The system is controlled by an Electronic Control Module (ECM), which monitors the engine conditions, then calculates the injection timing and air/fuel ratio according to the signals from the sensors. The ECM consists of a microprocessor, Random Access Memory (RAM), Read Only Memory (ROM) and input and output signal interface systems.

The MFI system consists of 2 operating modes:

Open Loop-air/fuel ratio is controlled by information programmed into the ECM by the manufacturer.
Closed Loop-air/fuel ratio is varied by the ECM based on information supplied by the oxygen sensor.

An electric fuel pump supplies sufficient fuel to the injection system and the pressure regulator maintains a constant pressure to the injectors. These injectors inject a metered quantity of fuel into the intake manifold in accordance with signals from the Electronic Control Module (ECM) or engine computer. After pressure regulation excess fuel is returned to the fuel tank.

The injectors have 2 modes (Injector Drive Timing) of operation:

Non-synchronous Injection (Simultaneous Injection)
Synchronous Injection (Sequential Injection)

Non-synchronous injection is activated during engine starting (cranking). There are 2 fuel injections, for each engine rpm, to all 4 cylinders. Also, during acceleration, fuel proportionate to the magnitude of acceleration, is injected to 2 selected cylinders during the intake and exhaust strokes.

Synchronous Injection is activated after the engine has started. The injectors are activated at the exhaust stroke of each cylinder in a sequential manner, according to crankshaft angle sensor signal. There is 1 injection per cylinder for every 2 crankshaft revolution, according to firing order.