Fleetwood FWD V8-300 4.9L (1993)
Evaporative Emission Control Canister: Description and Operation
Charcoal Canister
SYSTEM OPERATION
The Evaporative Emission Control System (EECS) uses the basic charcoal canister storage method. This method transfers fuel vapor from the fuel tank
to the charcoal canister storage device to hold the vapors when the vehicle is not operating. When the engine is running, the fuel vapor is purged from
the carbon element by intake manifold vacuum and is consumed in the normal combustion process.
CHARCOAL CANISTER
The EECS uses an inverted function charcoal canister. A single tube extends down the center of the canister to a liquid trap at the canister base. Fuel
vapor from the tank enters a port at the top of the canister. Vapor (and any liquid droplets) travels down the dip tube between the inner dip tube and the
outer tube wall. Any liquid present is trapped in the lower liquid well, away from the charcoal element. Fuel vapor is stored in the activated carbon
element until purged.
PURGE MODE
When a purge mode is commanded, stored fuel vapor is drawn into the inner dip tube through a calibrated orifice at the base of the tube. Any liquid
trapped in the liquid well is also drawn into the inner dip tube through a smaller calibrated orifice. Fresh air is drawn into the canister at the top mounted
vent.
The PCM operates a solenoid valve which purges the charcoal canister with ported vacuum at the throttle body. Under cold engine, "OPEN LOOP", or
idle conditions, the solenoid is de-energized by the PCM, which closes the purge solenoid and blocks vacuum to the canister. The canister will be
enabled (PCM energizes the solenoid) when:
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Coolant is above 80°C.
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Closed loop has been achieved for at least 30 seconds.