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 10
OPERATION
When engine coolant temperature rises above 129°F (54°C), a bi-metallic vacuum switching valve (BVSV) opens purge line between canister and throttle purge port. As engine speed increases to a moderate level, throttle valve opens purge port to manifold vacuum and canister vapors flow through purge line and into combustion chambers for burning.
As engine speed drops to idle, the throttle valve closes off purge port to manifold vacuum and canister purging stops.
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 tank port.
Hold other top canister port(s) closed and check that no carbon comes out of canister.
BI-METALLIC VACUUM SWITCHING VALVE (BVSV)
Drain engine coolant and remove valve. Cool the BVSV to below 95°F (35°C) in cool water. Blow air into a port and check that BVSV is closed. Heat the BVSV to above 129°F (54°C) in hot water. Blow air into port and check that BVSV is open. Apply liquid sealer to threads of BVSV when installing.
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.
On Camry, Cressida & Supra, blow air into canister purge port and check that air does not flow out of any other port. On all models, 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.