Hyundai Coupes/Sedans 1986-1993 Repair Guide

General Description


The feedback carburetor (FBC) system used on the Excel provides the capability to perform closed loop fuel control. It also provides the capability to control the secondary air system, the deceleration spark control system and the throttle opener system. The basic functions of this system are described below.

Input signals from a variety of sensors are fed to a microprocessor based Electronic Control Unit (ECU). The ECU then generates output signals for all of the controlled functions. The feedback carburetor is a 2-barrel, downdraft carburetor designed for closed loop system. When used with the closed loop system of mixture control, this carburetor includes special design features for optimum air/fuel mixtures during all ranges of engine operation. Fuel metering is accomplished through the use of three solenoid-operated on/off valves (jet mixture, enrichment and deceleration solenoids), adding or reducing fuel to the engine. The activation of the on/off valve is controlled by the length of the time current is supplied to the solenoid. The solenoid operates at a fixed frequency. By varying the amount of time the solenoid is energized during each cycle (defined as duty cycle), the air/fuel mixture delivered to the engine can be precisely controlled, The duty cycle to the solenoid is controlled by the ECU in response to the signals from the exhaust oxygen sensor, throttle position sensor. For more information on FBC systems refer to Emission Controls .