300Tdi Discovery
19
FUEL SYSTEM
6
DESCRIPTION AND OPERATION
Non - evaporative loss equipment
1. Throttle disc
2. Fuel cut-off valve
3. Two way valve
4. Charcoal canister
5. Purge control valve
6. Fuel filler cap
7. ECM
8. One way valve
Charcoal canister
A charcoal canister is used for the temporary storage
of fuel vapour from the fuel tank until the vapour can
be purged from the canister into the engine and
burned.
The charcoal canister is purged when the purge
control valve is open, fresh air is drawn through the
purge air hose, through the charcoal canister and into
a port in the inlet manifold.
Purge control valve
A purge control valve is operated by the ECM The
valve remains closed when the engine is cold and at
idling speed to protect engine tune and catalyst
performance. If the charcoal canister was purged
during cold running or at idling speed, the additional
enrichment in fuel mixture would delay catalyst light
off time and cause erratic idle. When the engine
temperature is above 75
°
C, the purge control valve
will be operational (modulated ON and OFF)
whenever the engine speed is above approximately
1600 rev/min. When the purge valve is opened, fuel
vapour from the charcoal canister is drawn into the
inlet manifold for combustion.
