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
The fuel evaporation system is controlled by a bi-metallic vacuum switching valve (BVSV) and a vacuum control valve (VCV). At low engine temperature, ported vacuum to the VCV is cut off and no fuel vapors are drawn into intake manifold.
When the engine is warmed to normal operating temperature, BVSV opens and allows ported vacuum to reach the VCV. When engine is running above idle, the ported vacuum signal opens VCV and manifold vacuum purges canister, drawing vapors into combustion chambers for burning.
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.
CANISTER
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.