Evaporative Emissions System: Description and Operation

Evaporative Emission Control System:

This system, consists of a non-vented fuel cap, charcoal canister, routing hoses, safety valve, thermocontact switch and an electric purge valve. The canister contains activated charcoal and is mounted on the right front side of the engine compartment. A hose connects the charcoal canister to the electric purge valve and another hose connects the electric purge valve to the intake system.

When the engine is cold the thermocontact switch, which is subjected to coolant temperature, does not allow the electric purge valve to operate, preventing fuel vapors from flowing to the intake system.

When the engine is at normal operating temperature, the thermocontact switch opens the circuit to the electric purge valve allowing fuel vapor to flow between the charcoal canister and the intake manifold. To prevent possible fuel leaks at the accumulator (AC), the tap located at the back of the accumulator is connected to the fuel return line going to the fuel tank.

Safety Valve:

When the engine is not operating, fuel vapors from the fuel tank are transmitted through a metered orifice in the safety valve, and flow to the charcoal canister where the fuel vapors are absorbed by the activated charcoal. In the event the safety valve metering orifice becomes obstructed, causing a vacuum within the fuel tank, fuel tank venting is accomplished through portion A of the safety valve. If the safety valve is tilted more than 45° it will stop the flow of fuel from the fuel tank (roll-over condition).