Deceleration Fuel-Cut System Toyota Tercel L30

DESCRIPTION

This system aids in controlling exhaust emissions and improving engine performance during prolonged periods of deceleration. The system cuts off the fuel or reduces the amount of fuel in the mixture. The air/fuel ratio becomes lean during deceleration, therefore preventing afterburning and overheating.

OPERATION

On carbureted models, the system consists of a fuel-cut solenoid, vacuum switch, computer and wiring. A slow speed circuit in the carburetor operates except during prolonged periods of deceleration at high engine speeds. Under these conditions, a vacuum switch or computer turns off the fuel-cut solenoid valve creating a lean mixture.

On EFI models, the system consists of the ECU and throttle position sensor. The ECU adjusts the fuel injection duration depending on engine RPM.

Scheme 53

Scheme 54

FUEL-CUT SOLENOID VALVE

Remove solenoid valve from engine and apply battery voltage to terminals. Solenoid should click if operating properly. Check "O" ring for damage and replace if necessary. Reinstall valve. With engine at idle, unplug fuel-cut solenoid connector. Engine should idle rough or die.

THROTTLE POSITION SWITCH

Note. Perform this test with cooling fan off.

Corolla & Tercel Sedan

1. Start engine and allow to warm to operating temperature. Connect tachometer to engine. Disconnect throttle switch connector. Using ohmmeter, put one terminal on throttle switch connector and other to carburetor body. Slowly raise engine speed.
2. Check throttle position switch setting speed when ohmmeter shows continuity. Continuity setting speed is 1800 RPM on Corolla models and 1400 RPM on Tercel models. If setting speed is incorrect, adjust by turning throttle position switch adjusting screw.

Land Cruiser, Pickup, 4Runner & Tercel Wagon

Disconnect wiring connector from switch. Using ohmmeter, check for continuity between terminal and body of switch with engine stopped. Start the engine and warm to normal operating temperature. Check that there is no continuity between switch terminal and switch body. Replace switch if defective.

Scheme 55

Note. Perform these procedures quickly to avoid overheating and damage to catalytic converter.

1. Connect tachometer to engine. Start engine and check that engine idles properly. On Corolla models, disconnect the throttle position switch connector. Gradually increase engine speed to 2300 RPM and check that engine RPM fluctuates.
2. Reconnect throttle position switch connector. Check that engine operation returns to normal.
3. On Tercel Sedan models, raise engine RPM to 2200 or more and ensure engine runs steady. With engine at 3000 RPM, use a screwdriver to press in tip of throttle position switch. Engine should hesitate.
4. Release throttle position switch. Engine should return to 3000 RPM. With engine at idle, disconnect fuel-cut solenoid valve connector. Engine should run rough and eventually stop.

1. Connect tachometer to engine. Start engine and check that engine idles properly. On Land Cruiser, 4Runner and Pickup models, pinch off vacuum hose to vacuum switch. Gradually increase engine speed to 2000 RPM (3000 RPM on Pickups & 4Runners). Engine should misfire slightly between 1200-2000 RPM (1800-3000 RPM on Pickups & 4Runners).
2. Release the pinched hose and increase engine speed to 2000 RPM (3000 RPM on Pickups & 4Runners). Engine operation should return to normal.
3. On Tercel Wagon models, disconnect vacuum switch connector. Gradually increase engine speed to 2300 RPM. Engine should run rough between 1900-2300 RPM and RPM should fluctuate as engine speed is raised.
4. Reconnect vacuum switch connector. Raise engine speed to 2300 RPM, checking to see that engine runs smoothly. If engine responds as indicated, system is operating normally.

FUEL-CUT RPM

Connect tachometer to engine. Allow engine to reach normal operating temperature. Disconnect throttle position sensor. Using a jumper wire, short-circuit terminal IDL with terminal E1 or E2 of the connector. (Scheme 56)& (Scheme 57). Gradually raise engine speed and check that there is fluctuation between fuel-cut and fuel-return points. See FUEL-CUT RPM SPECIFICATIONS chart.

Scheme 56

Scheme 57

FUEL-CUT RPM SPECIFICATIONS

See also:
• FUEL-CUT RPM SPECIFICATIONS