Feedback Carburetor System Toyota Tercel L20

DESCRIPTION

System contains various components which enable HC, CO, and NO(x) to be reduced in addition, driveability and fuel economy are improved.

OPERATION

Carburetor primary side main air bleed and slow air bleed volume are controlled by a signal from the Oxygen sensor. This maintains optimum air-fuel mixture.

ELECTRONIC BLEED CONTROL VALVE (EBCV)

1. Using an ohmmeter, ensure there is no continuity between positive terminal of EBCV connector and EBCV body. If continuity is indicated, replace shorted EBCV.
2. Using an ohmmeter, measure resistance between terminals of EBCV connector. Ohmmeter reading should be 11 -13 ohms at 68°F (20°C). If reading is incorrect, replace open EBCV.

Scheme 1

Scheme 2

OXYGEN SENSOR

1. Warm engine to normal operating temperature. Connect voltmeter to check connector. See «CHECK CONNECTOR LOCATION»(/toyota/tercel/l20-1982-1988/remont/testing-diagnostics/#feedback-carburetor-system) table for location of connector.
2. Ensure positive probe is connected O "Ox" terminal and negative probe is connected to terminal "E". Start and race engine to 2500 RPM for about 90 seconds. Maintain engine speed at 2500 RPM and ensure voltmeter needle fluctuates 8 times or more in 10 seconds within 0 - 7 volts. If voltmeter fluctuates as indicated, oxygen sensor is okay.
3. If not, inspect hoses and wiring of fuel feedback control system and air suction system. If no problem is found, replace oxygen sensor.

CHECK CONNECTOR LOCATION

Scheme 3

Wagon

To test vacuum switch "A", use an ohmmeter and check for continuity between switch terminal and switch body. Start engine and warm to normal operating temperature. Using an ohmmeter, ensure there is no continuity between switch terminal and body. For vacuum diagram, see VACUUM DIAGRAMS article.

To test vacuum switch "B", use an ohmmeter and ensure there is no continuity between switch terminal and switch body. Start engine and warm to normal operating temperature. Using an ohmmeter, ensure continuity is present between switch terminal and body. For vacuum diagram, see VACUUM DIAGRAMS article.

Sedan

Using an ohmmeter, check for no continuity between switch terminals. Apply over 3 in. Hg vacuum to vacuum switch. Using an ohmmeter, ensure continuity is present between switch terminals. For vacuum diagram, see VACUUM DIAGRAMS article.

COLD ENGINE

Coolant temperature should be below 45°F (7°C). Disconnect vacuum hose from vacuum switch. (Scheme 5) Start engine and ensure no vacuum can be felt at disconnected vacuum hose. Reconnect vacuum hose.

WARM ENGINE

1. Warm engine to normal operating temperature. Disconnect Electronic Bleed Control Valve (EBCV) connector. Ensure engine speed is maintained at 2500 RPM.
2. Reconnect connector and ensure engine speed drops about 300 RPM momentarily. With engine idling repeat test. Engine RPM should not change. Disconnect vacuum hose from vacuum switch and repeat test. Engine RPM should not change. If no problem is found, system is okay.

Computer Controlled Emission System (Sedan). Scheme 4

Computer Controlled Emission System Wiring Diagram (Wagon). Scheme 5

See also:
• CHECK CONNECTOR LOCATION