Fuel Delivery and Air Induction: 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. Refer to COMPUTERIZED ENGINE CONTROLS for information on the ECU, sensors and self-diagnostic system.

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 enriching 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)

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. Refer to COMPUTERIZED ENGINE CONTROLS for information on diagnosis and testing.