Fuel evaporation control system function

P47.30-2061-05

12 Intake manifold

17 Fuel rail

45 Fuel filler neck

55/1 Fuel filter with integrated fuel pressure regulator

71 Check valve

72 Float valve

75 Fuel tank

75/1 Expansion reservoir

77 Activated charcoal canister

77/1 Vent/breather line

M3 Fuel pump

N3/10 ME-SFI [ME] control unit

Y58/1 Purge control valve

A Electrical line

B Fuel pipe

C Purge line

The evaporative emission control system prevents fuel vapors escaping to atmosphere. The fuel vapors are stored for this purpose in the activated charcoal canister and burnt under prescribed preconditions in the engine.

1) Refuelling

The expansion reservoir with float valve is designed to prevent fuel flowing to the activated charcoal canister during refueling (overfilling).

2) Air release from fuel tank

The fuel tank is vented through the activated charcoal canister. In this case, the fuel vapors flow to the activated charcoal canister, where they are stored or drawn into the intake manifold in case of released regeneration.

3) Aeration of the fuel tank

Air is admitted through the activated charcoal canister. This is done via the activated charcoal canister, whereby air is drawn out of the vent line and / or fuel vapors from the activated charcoal canister into the fuel tank.

4) Activated charcoal regeneration

When the engine is running, the fuel vapors stored in the activated charcoal canister, are drawn off through the purge control valve and combusted in the engine.

The check valve in the purge line prevents the boost pressure building up toward the activated charcoal canister.

The purge control valve is actuated by the ME-SFI [ME] control unit for regeneration, if:

 coolant temperature > 70°C

 engine start >2 minutes previously

 engine not in the overrun mode

 engine not in the lambda adaptation phase

The purge quantity is determined by constantly opening and closing the purge control valve with on periods of varying lengths.

The idle speed control prevents changes in engine speed resulting from purging. A richer or leaner fuel-air mixture is produced in line with the charge of the activated charcoal canister with fuel vapors.