Evaporative Emission Control System Function
Evaporative Emission Control System Function
Shown on Engine 119
75 Fuel tank
77 Activated charcoal canister
N3/10 ME control unit
Y58/1 Purge control valve a Pressurization line
Shown on engine 120
75 Fuel tank
77 Activated charcoal canister
93 Expansion reservoir (only with optional ski bag)
M16/3 Right EA/CC/ISC actuator - Position on left of engine
M16/4 Left EA/CC/ISC actuator - Position on right of engine
N3/11 Left ME-SFI [ME] control unit
N3/12 Right ME-SFI [ME] control unit
Y58/2 Switchover valve - Left regeneration
Y58/3 Switchover valve - Right regeneration
a Pressurization line
The evaporative emission control system prevents fuel vapors escaping to atmosphere. This is done by storing the fuel vapors temporarily in the activated charcoal canister.
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 activated charcoal canister is purged (re-generated) at:
- coolant temperature > 70°C
- blocking time after engine start elapsed, approx. 2 minutes
- Engine not in deceleration mode
The purge quantity is controlled by the ME-SFI control unit operating the purge control valve. The purge quantity is determined by constantly opening and closing the purge control valve for on and off periods of various 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.
Air admission to fuel tank
Air is admitted through the activated charcoal canister. This is done by the activated charcoal canister (77) drawing air out of the air admission line (a) and fuel vapors out of the activated charcoal canister into the fuel tank (75), respectively.
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 if purging is activated at that moment, they are drawn off into the intake manifold.
Vent valve
On vehicles fitted with a vent valve the fuel tank is vented from a pressure of 30 to 50 mbar, and air admitted at a vacuum of 1 to 16 mbar. In addition, this prevents overfilling the fuel tank.
(USA) as of MY 98
During refueling the fuel vapors are collected at the filler neck and passed to the activated charcoal filter (ORVR = Onboard Refueling Vapor Recovery). Large activated charcoal canister.
Engines with charging (compressor or turbocharger)
A check valve in the purge line prevents the boost pressure building up toward the activated charcoal canister.