The feedback carburetor system is only used on 1986-89 1.3L engines. The primary purpose of this system is to maintain a controlled air/fuel mixture, which reduces the emission of Oxides of Nitrogen (NOx), hydrocarbons, carbon monoxide, and to improve fuel economy at the same time. The system is composed of an oxygen sensor and the Engine Control Module (ECM). The ECM uses information gathered by the oxygen sensor to manipulate the mixture control solenoid in the carburetor, thereby altering the air/fuel mixture of the carburetor.
The ECM controls many systems, such as the fuel cut system, idle-up system, bowl vent system, EGR system and the secondary throttle valve system, as well as the feedback carburetor system. The ECM is located under the glove compartment of the instrument panel.
The ECM receives incoming information from several components, namely: oxygen (O2) sensor, Engine Coolant Thermal (ECT) switch, Throttle Position (TP) micro-switches, ignition coil, 5th switch, Barometric Pressure (BP) switch, and underhood temperature sensor. The ECM also monitors the heater fan circuit, the rear defogger circuit (if equipped), and the tail light, side marker light and license plate light circuits for excessive electrical loads.
The oxygen sensor and engine coolant temperature sensors are described later in this section, under Electronic Engine Controls.
The two throttle position switches (wide open switch and idle switch) are mounted on the carburetor, and indicate the position of the carburetor throttle. The ECM uses this information in conjunction with the other sensors to determine the proper amount of fuel that should be introduced into the air stream for the correct air/fuel mixture.
The ignition coil is used by the ECM to determine engine speed (rpm).
The 5th switch is designed to send a signal to the ECM whenever the transmission gearshift lever is moved to the 5th gear position.
The barometric pressure sensor is used by the ECM to determine the altitude of the vehicle. Since air density changes with respect to changes in altitude, the amount of fuel needed for the proper air/fuel mixture is different at various altitudes.
The underhood temperature sensor is designed to monitor the temperature of the air in the engine compartment, and to relay that information to the ECM, which uses the information to correctly alter the air/fuel mixture. When the air temperature is low (cold), the ECM enrichens the mixture slightly to allow for better combustion. Likewise, when the air temperature is high (hot), it leans the mixture out slightly.
See Figures 1 and 2
The operation of the feedback carburetor system can be conveyed by the CHECK ENGINE light in the instrument cluster. The CHECK ENGINE light automatically flashes at the 50,000 mile (80,000km), the 80,000 mile (12,000km), and the 100,000 mile (162,000km) marks when the engine is warmed up. The automatic flashing indicates that the feedback carburetor system is functioning properly.
Should any of the following conditions occurs, the feedback system can be tested manually.
Inspect the feedback carburetor system, as follows:
- Turn the cancel switch or check switch, located under the driver's side instrument panel, on.
- Turn the ignition switch ON , without starting the engine. At this time, the CHECK ENGINE light should illuminate, but NOT flash. If the light does not illuminate, ensure that the light bulb is not blown and inspect the wiring harness for an open or short circuit.
- After confirming proper CHECK LIGHT function, start the engine and allow it to reach normal operating temperature.
Once the engine reaches normal operating temperature, run the engine at 1500-2000 rpm. While operating the engine at this speed, ensure that the CHECK LIGHT flashes, which indicates the system is functioning properly. If the light does not flash, the problem could be caused by one or more of the following:
Defective oxygen sensor.
- Check the preceding switches and sensors, then replace any that require it. Retest the system.
- After ensuring the CHECK ENGINE light flashes when it should, turn the cancel switch off.
- Turn the engine OFF .
The testing of the individual feedback carburetor system sensors and switches are covered later in this section, under Electronic Engine Controls.
REMOVAL & INSTALLATION
The removal and installation of the individual feedback carburetor system sensors and switches are covered later in this section, under Electronic Engine Controls. For ignition coil removal, refer to Engine Electrical of this repair guide.