Feedback Carburetor System Toyota Tercel L30

DESCRIPTION & OPERATION

Toyota carburetor models use a Feedback Control (FBC) System. By means of a signal from Oxygen (O2) sensor, carburetor primary side main air bleed and slow air bleed volume are controlled to maintain optimum air-fuel mixture. This reduces HC, CO, and NOx in addition to providing better driveability and fuel economy.

All models use an Electronic Air Bleed Control Valve (EBCV). Two vacuum switches are used on Tercel Wagon models. (Scheme 110)and (Scheme 111).

Scheme 109

1. Disconnect electrical connector from EBCV. Connect an ohmmeter from positive terminal and EBCV body. (Scheme 109) There should be no continuity. If continuity is present, replace EBCV. NOTE: EBCV is different in shape on the different models. Testing procedures are the same.
2. Connect an ohmmeter between both terminals of EBCV. Resistance should be 11-13 ohms at 68°F (20°C). If resistance is not within specifications, replace EBCV.
3. On all models, also check EBCV with vehicle at normal operating temperature by disconnecting EBCV electrical connector. Increase engine speed to 2500 RPM. Reconnect connector and check for decrease of 300 RPM. Stop engine.
4. Restart and allow engine to idle with EBCV disconnected. Reconnect connector and check that engine RPM does not change. Disconnect vacuum hose from vacuum switch. Increase engine RPM to 2500 RPM with EBCV disconnected. Reconnect EBCV and check that RPM does not change. If fault is noticed, check each component.

Tercel Sedan

Ensure oil temperature is below 41°F (5°C). Disconnect vacuum hose from vacuum switch. Start engine and check for vacuum at disconnected hose. Vacuum should not be present. Warm vehicle above 66°F (19°C). Vacuum should be present. Replace BVSV as necessary.

Scheme 110

Scheme 111

Disconnect vacuum switch electrical and vacuum connectors. Attach ohmmeter between switch terminals. No continuity should be present. Apply 4.3 in. Hg to vacuum switch. Continuity should now be present.

Tercel Wagon ("A" & "B")

1. Disconnect electrical connector at vacuum switch "A". Connect ohmmeter to switch terminal and switch body. Engine coolant must be cold. Continuity should be present. Warm vehicle to normal operating temperature. No continuity should be present.
2. Disconnect electrical connector at vacuum switch "B". Connect ohmmeter to switch terminal and switch body. With engine coolant cold, there should be no continuity. With engine at normal operating temperature, there should be continuity. Replace as necessary.

Tercel Wagon

With coolant temperature below 45°F (7°C), disconnect vacuum switch "B" (Tercel Wagon). (Scheme 111) Start engine and ensure no vacuum is present at hose. Replace TVSV as necessary.

OXYGEN (O2) SENSOR CHECK

1. Warm vehicle to normal operating temperature. Connect positive voltmeter probe to O2 sensor terminal of check connector. See «CHECK CONNECTOR LOCATION»(/toyota/tercel/l30-1986-1990/remont/testing-diagnostics/#feedback-carburetor-system) table in this article. Connect negative probe to terminal "E1". (Scheme 112)and (Scheme 113). CHECK CONNECTOR LOCATION Vehicle Location Tercel Sedan (1) Next to Clutch Reservoir, on Firewall Tercel Wagon (1) Right Fender Below Wiper Motor (1) (Scheme 112)and (Scheme 113).
2. Start engine and increase RPM to 2500 RPM for 90 seconds. Maintain 2500 RPM and monitor voltmeter needle. Voltmeter should fluctuate specified volts, 8 times or more within 10 seconds. See «OXYGEN O2 SENSOR VOLTAGE FLUCTUATION»(/toyota/tercel/l30-1986-1990/remont/testing-diagnostics/#feedback-carburetor-system) table in this article. OXYGEN O2 SENSOR VOLTAGE FLUCTUATION Vehicle Voltage Tercel Sedan 1-5 Tercel Wagon 0-7
3. If check tests okay, O2 sensor is operating properly. If check fails, check each component, hose and wiring of feedback system. If no problem is found, replace O2 sensor.

Scheme 112

Scheme 113

Scheme 114

Scheme 115

See also:
• CHECK CONNECTOR LOCATION