XJ6 Purge Valve

The purge valve allows fuel vapor to be burned in the engine or in other words, the Fuel tank is vented through the charcoal canister, where vapor is stored, until it is purged into the intake manifold by the canister purge valve. The ECM or PCM controls the flow of fuel vapor by controlling the duty cycle of the canister purge valve. App $35 new.

The purge valve is supposed to click, its job is to flow fuel vapors into the engine from the fuel tank for emissions. The clicking sometimes can be louder due to the routing of the purge vapor lines at the firewall area. The clicking of the purge solenoid can cause the hose to vibrate against the firewall and make the purge valves normal operation heard in the car. This cab be "repaired" by adding some foam tape. 

An exploded diagram with parts list can be found HERE.
Second design HERE.

The canister contains activated charcoal and stores the unburnt gas from the cylinders when the engine is shut off as well as the fumes from the gas tanks. In the Haynes repair manual it is recommended to replace the canister at about every 25,000 miles. The problem is it costs $108 for the canister. 

Stick a finger in the end of the hose to try to detect wetness. Or you might have possibly noticed a small puddle of gas on the ground near this area which would lead you to determine that the canister is oversaturated.

In any case, if the canister hasn't been replaced in quite a while, remove it and pour carbureator cleaner in the vent pipe, shake the daylights out of it then drain the cleaner. This should remove the build up from the gas vapors and work for awhile for you.

The Evaporative System (EVAP) prevents the fuel vapors from the fuel tank from escaping into the atmosphere. The EVAP system traps the fuel vapors and temporarily stores them in the charcoal canister. When the engine is running and other conditions allow, the fuel vapors are drawn by the engine vacuum from the EVAP charcoal canister and into the engine air intake. To balance the air pressure in the fuel tank, some air is allowed into the charcoal canister when needed. 
The engine computer periodically runs the self-test to see if the Evaporative system is sealed tight. For the time of the test, the engine computer closes the vent valve. The trouble code P0449 means that the engine computer has detected a malfunction in the electric circuit that controls the vent valve/solenoid. 
It could be a problem with the vent valve/solenoid itself or with the wiring that runs from the engine computer to the vent valve/solenoid. Sometimes the wires that run to the vent valve/solenoid get rubbed through or shorted. A bad connection at the vent valve/solenoid connector, a problem with the power supply or ground or an issue with the engine computer (ECM) itself can also cause the code P0449. 
Typically the vent valve/solenoid is located somewhere closer to the fuel tank, not too far from the charcoal canister at the back of the vehicle. Many newer cars have the vent valve attached to the charcoal canister. The diagnostic procedure for the code P0449 usually involves operating the vent valve solenoid with a scan tool and testing the power supply voltage and the ground at the vent valve/solenoid, as well as checking its resistance.

P0455 - Evaporative Emission System Leak Detected (Large Leak/No Flow)

The Evaporative System (EVAP) prevents the fuel vapors from the fuel tank from escaping into the atmosphere. The EVAP system traps the fuel vapors and temporarily stores them in the charcoal canister. When the engine is running and other conditions allow, the fuel vapors are purged from the charcoal canister into the engine air intake to be burned. The purge flow is controlled and monitored by the engine computer (ECM). The Evaporative System is sealed and the ECM can detect if there is a leak. The diagnostic trouble code P0455 - Evaporative Emission System Leak Detected (Large Leak/No Flow) means that the ECM has detected a large leak or no purge flow. A gas cap is the first thing to check in this case. The problem could also be caused by a cracked or disconnected tube, damaged charcoal canister, blockage in the fuel vapor lines or hoses, bad purge valve, stuck open canister vent valve, etc.