Fuel Evaporation System: Operation
When the fuel tank vapor pressure exceeds a pre-set limit, the pressure relief valve opens and vapors flow into canister for storage. The pressure relief valve also allows air to enter the tank when vacuum exceeds a pre-set limit. On the XJS HE models, the pressure relief valve is set to open at 2 psi.
When the engine is warming up on XJ6 models, the purge hose is shut off by an energized solenoid valve. After engine coolant temperature exceeds 113°F (45°C), the valve opens since current no longer passes through a thermal switch (also part of air injection system on Federal models).
When the engine is warming up on XJS HE models, a timer/relay switch delays purge valve opening for 45 seconds after engine is started. This delay allows catalytic converters to warm up to efficient operating temperature.
On both the XJ6 and XJS HE models, the purge line restrictor limits maximum purge air flow rate.