Computers and Control Systems: Description and Operation

Component Schematic - Federal And Canadian Models:

Component Schematic - California Models:

Toyota carbureted models utilize a Feedback Control System to control fuel delivery and carburetor operation during a variety of driving situations. The Electronic Control Unit (ECU) receives signals from the Oxygen Sensor, distributor and various other sensors, and monitors air/fuel mixture by means of an Electronic Air Bleed Control Valve (EBCV). This process reduces exhaust emissions in addition to providing improved driveability and fuel economy. California models are equipped with a self-diagnostic function built into the ECU.


FEEDBACK CARBURETOR (FBC) SYSTEM

The carburetor main air bleed is opened and closed by the EBCV, which is controlled by the ECU. The ECU senses engine operation mode by the use of one or two vacuum switches. The EBCV allows additional air into the air bleed as required, thus richening or leaning the air/fuel mixture. On Federal and Canadian models, the High Altitude Compensation System also controls EBCV operation. (Refer to EMISSION CONTROLS for more information)


COLD MIXTURE HEATER (CMH) AND FUEL HEATER SYSTEM

The ECU uses the water temperature sensor signal to activate the CMH relay and supply current to the heater elements in the base of the carburetor and in the float bowl. This aids with engine warm-up by pre-heating the fuel until the engine reaches normal operating temperature.


DECELERATION FUEL-CUT SYSTEM

This system deletes fuel to the carburetor slow circuit to prevent exhaust system overheating and afterburning on deceleration. The ECU operates the Fuel-cut Solenoid based on input from the throttle switch and engine rpm.


SELF-DIAGNOSTIC FUNCTION (CA. ONLY)

The Electronic Control Unit (ECU) for the FBC, contains a self-diagnostic system that will store failure codes associated with the fuel and emission control systems. The ECU will analyze signals from various sensors and actuators and detect any system malfunctions. An instrument panel "CHECK ENGINE" lamp will light to indicate when a system defect occurs. The technician can then extract these failure codes, follow the testing procedures and use the information to repair the malfunction.