Fuel Evaporation System Toyota 4Runner I

DESCRIPTION

The fuel evaporation system is designed to prevent the escape of raw fuel vapor into the atmosphere. Components include a sealed fuel tank with integral expansion chamber, vacuum relief filler cap, charcoal canister(s) with 2 or 3 integral check valves, and outer vent control valve.

Additional components include vacuum switching valve, emission computer, temperature switch, speed sensor, and connecting lines and hoses.

When fuel vapor pressure builds in tank, a check valve in canister opens and vapor flows into canister for storage. When vacuum forms in tank, a check valve in canister opens and stored vapor is drawn into fuel tank. If fuel tank vacuum should increase above a pre-set level, a vacuum relief valve opens in filler cap and fresh air flows into fuel tank to prevent tank collapse.

PICKUP & 4RUNNER - CARBURETED

When the engine is not running, fuel tank vapor flows through vent line into canister for storage. Float bowl vapor flows through outer vent control valve into canister for storage when ignition is off.

When engine is running (above 16 MPH with coolant temperature above 131°F (55°C), the vacuum switching valve (VSV) opens to allow canister vapor to be drawn into intake manifold for burning. The VSV is an electrically operated solenoid-type valve that is opened and closed by the emission computer. The computer opens and closes the valve based upon input signals from the speed sensor and/or temperature switch.

PICKUP & 4RUNNER - FUEL INJECTED

When the engine is not running, fuel tank vapor flows through vent line into canister for storage. A check valve in canister's purge port prevents vapor from flowing out of canister through purge line.

When engine speed increases to a moderate level, throttle valve opens purge port to manifold vacuum and canister vapor flows through purge line into combustion chambers for burning. When the throttle valve closes, it shuts off manifold vacuum to purge port and canister purging stops.

MAINTENANCE

Inspect fuel tank, canister, vacuum relief filler cap, lines and hoses for damage, leaks, and deterioration every 60,000 miles or every 6 years. Replace gasket in vacuum relief filler cap.

To clean charcoal canister filter, remove hoses from canister and apply 43 psi (3 kg/cm 2 ) air pressure to the fuel tank port.

Hold other top ports closed and ensure that no carbon comes out of bottom port of canister.

CHARCOAL CANISTER

1. Check for clogged filter and/or stuck check valve by blowing low pressure compressed air into canister tank port. Check that air flows freely out of other canister ports.
2. On fuel injected Pickup and 4Runner, blow air into canister purge port and check that air does not flow out of any other port.
3. On carbureted Pickup and 4Runner, blow air into the purge port and check that air flows freely through other ports. Replace canister if it does not operate as outlined.

When testing outer vent control valve, note that valve is moved by manifold vacuum and held by the solenoid. The solenoid cannot move the valve.

1. Disconnect outer vent hose from carburetor. Blow air into outer vent pipe and check that valve is open. Start the engine. With the engine idling, blow air into outer vent pipe and check that valve is closed.
2. Unplug the wiring connector from the solenoid. Using an ohmmeter, check the valve's resistance between the positive terminal and the solenoid body. Resistance should be 63-73 ohms at 68°F (20°C).

1. Using 3-way connector, connect a vacuum gauge in the hose between VSV and canister. Place gauge near driver's seat and warm engine to normal operating temperature.
2. Test drive vehicle and ensure vacuum gauge indicates zero at speeds below 7 MPH. Check that vacuum gauge indicates manifold vacuum at speeds above 16 MPH. If problem is found, inspect speed sensor and VSV.

1. Jack up and support one rear wheel off ground. Release parking brake. Place shift lever in Neutral. On 4WD models, ensure transfer case lever is in "2H" position.
2. Unplug wiring connector from computer. Computer is located at left kick panel. Test "ON-OFF" cycles of speed sensor using an ohmmeter. (Scheme 12) Insert a 10-ohm resistor in series with positive ohmmeter lead and insert lead in rear of connector. Connect negative terminal to ground.
3. Slowly turn wheel, checking to see that ohmmeter needle deflects consistently. If ohmmeter needle does not deflect, check that sensor leads are firmly connected to rear of speedometer. If connections are okay, replace speedometer assembly.

Testing Speed Sensor (Carbureted Pickup & 4Runner) Insert positive lead into rear of connector. Scheme 12

1. Drain engine coolant and remove switch from intake manifold. Cool switch below 109°F (43°C). Using an ohmmeter, check that there is continuity between switch terminal and body.
2. Heat switch in hot water to temperature above 131°F (55°C). Check that there is no continuity. Replace switch if it does not operate as outlined. Apply liquid sealer to threads before installation.

VACUUM SWITCH

Disconnect electrical connector at switch. Ensure there is continuity between switch terminal and switch body. Start and warm engine to normal operating temperature. There should be no continuity between switch terminal and switch body. Replace switch if it does not operate as outlined.

1. Disconnect VSV connector and connect battery voltage to VSV terminals. Air should pass through valve with voltage applied. Remove battery voltage and check that air flow is blocked.
2. Using an ohmmeter, check that there is no continuity between positive terminal of VSV and valve body.
3. Using an ohmmeter, check resistance between VSV terminals. Resistance at 68°F (20°C) should be 38-44 ohms. Replace VSV if it does not operate as outlined.

FUEL ODOR OR GAS LEAKS

Disconnected or cracked fuel vapor line or defective components in system. Check all lines and fittings and check operation of system.

FUEL TANK OR EXPANSION TANK DEFORMED

Canister clogged, vacuum relief filler cap defective (valve in cap inoperative), hoses clogged or kinked.

ROUGH ENGINE OPERATION

Check vacuum hose between vacuum switching valve (if equipped) and intake manifold for damage and proper connections. Check for malfunctions in other valves and be sure all vacuum hoses are tight and in good condition.