DESCRIPTION
Toyota fuel evaporation control system is designed to prevent the escape of raw fuel vapors into the atmosphere. This is accomplished with a special fuel tank, filler cap, charcoal fuel vapor storage canister(s), and various control valves (depending on vehicle application).
When fuel vapor pressure builds in tank, a check valve in canister opens and vapors flow into canister for storage. When vacuum forms in tank, a check valve in canister opens and stored vapors are 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 preventing tank collapse.
Check Valves in Charcoal Canister. Scheme 15
CARBURETED MODELS
When the engine is not running, fuel tank vapors flow through vent line into canister for storage. Float bowl vapors flow through the outer vent control valve into canister for storage when the ignition key is in the "OFF" position.
When the engine is running above 1600 RPM and coolant temperature is above 131°F (55°C), the vacuum switching valve (VSV) opens and canister vapors are drawn into intake manifold for burning. The VSV is an electrically operated solenoid type valve and is opened and closed by a computer. This computer receives input signals from a speed sensor and thermo switch.
MAINTENANCE
Inspect fuel tank, canister, filler cap, lines and hoses for damage, leaks, and deterioration every 60,000 miles or every 4 years. Replace gasket in filler cap.
To clean charcoal canister filter remove hoses from canister and apply 43 psi (3.02 kg/cm 2 ) of air pressure to the outer vent control valve port.
Hold other top canister port(s) closed and check that no carbon comes out of canister.
Carbureted Vehicles
- Disconnect VSV connector and connect battery voltage and ground to VSV terminals. Air should pass through valve with voltage applied. Remove battery voltage and check that air flow is blocked.
- Using an ohmmeter, check that there is no continuity between positive terminal of VSV and outside of valve body.
- 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.
- Using 3-way connector, connect a vacuum gauge in the hose between the VSV and canister. Set the gauge at the driver's seat and warm up the engine. Check that the vacuum gauge indicates zero at low speeds (below 1180 RPM).
- Check that vacuum gauge indicates manifold vacuum at middle and high driving speeds (above 1600 RPM). If problem is found, inspect speed sensor and VSV.
Drain engine coolant and remove switch from the intake manifold. Cool switch below 109°F (43°C). Using an ohmmeter, check that there is continuity between switch terminal and body. Heat switch above 131°F (55°C) in hot water. Check that there is no continuity. Apply liquid sealer to threads and reinstall.
OUTER VENT CONTROL VALVE
Disconnect the hoses from the valve. Check that the valve is open when the ignition is in the "OFF" position. Check that the valve is closed when the ignition switch is in the "ON" position. If the valve does not operate as outlined, check fuse and wiring connections.
CANISTER
On all models, 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. Replace canister 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, fuel filler cap defective (valve in cap inoperative), hoses clogged or kinked.
ROUGH ENGINE OPERATION
Check vacuum hose between vacuum solenoid 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.