Fuel Evaporation Control - Porsche 928 S 1984 Owner's Manual

Fuel Evaporation Control

Fuel Tank Venting
The expansion chamber and the safety valve prevent
fuel from escaping to the outside at extreme high out-
side temperatures and when the car is driven or parked
at an incline or in any other nonlevel position. The safety
valve works as a restrictor in the tank vent line between
the expansion chamber and the carbon canister.
1 Fuel tank
2 Fuel line
3 Fuel pump
4 Fuel pressure damper
5 Fuel filter
6 Fuel pressure regulator
7 Fuel injection lines
8 Air distributor/intake manifolds
9 Fuel return line
10 Control valve
11 Expansion chamber
12 Tank vent line
13 Safety valve
14 Carbon canister
15 Air cleaner
16 Engine compartment
17 Throttle plate
18 Injection valve
19 Filler cap
20 Vacuum control line
21 Temperature controlled ON/OFF valve
22 Vacuum controlled ON/OFF valve
Vapor Control System and Storage
When the fuel tank is filled, vapors are collected in the
expansion chamber and filler tube by a vent line leading
the vapors to the activated carbon canister where they
are stored as long as the engine does not run. During
running of the engine, the vapors are stored in the ac-
tivated carbon canister as long as the temperature con-
trolled ON/OFF valve is in the OFF-position.
The temperature controlled ON/OFF valve stops purg-
ing of the canister during all other running conditions of
the engine if the coolant temperature of the engine is
below a defined temperature.
Purge System
Fuel vapors from the carbon canister will be mixed with
fresh air taken from the engine compartment. This mix-
ture will be directed via two vacuum controlled valves to
the air intake system housing.
The temperature controlled ON/OFF valve has the fol-
lowing functions:
To stop purging of the canister during idle (the rich vapor
flow from the canister would influence the mixture char-
acteristic).
To allow purging of the canister during all other running
conditions of the engine.
The vacuum controlled ON/OFF valve has the function
to control the purge flow (high intake vacuum means low
purge flow and low intake vacuum means high purge
flow).
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