Evaporative Emissions System: Description and Operation

GF47.30-P-3013M Fuel Evaporation Control System Function
- MODEL 215, 220 with ENGINE 275.950
- MODEL 230 with ENGINE 275.951 up to Model Year 8
- MODEL 216, 221 with ENGINE 275.953 up to Model Year 8
- MODEL 230 with ENGINE 275.954 up to Model Year 8
- MODEL 215, 220 with ENGINE 275.980
- MODEL 230 with ENGINE 275.981 up to Model Year 8
- MODEL 216, 221 with ENGINE 275.982 up to Model Year 8
- MODEL 240 with ENGINE 285.950
- MODEL 240 with ENGINE 285.980





Illustrated model 215, 220, 230, 240
12 Intake manifold
71 Check valve Activated charcoal canister
75 Fuel tank
76 Vent valve (Model 215, 220, 230, 240 except (United States of America))
77 Activated charcoal canister
N3/10 ME-SFI control unit
Y58/1 Purge control valve
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 (regenerated) at:
- coolant temperature greater than 70 °C
- the 2 minute delay after engine start has elapsed
- Engine not in the overrun 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. The fuel vapor flows into the activated charcoal canister, where it is stored and drawn off into the intake manifold when the purging process is enabled.

Vent valve , model 215, 220, 230, 240 (without (United States of America))
On vehicles fitted with a vent valve (76) the fuel tank is vented at an overpressure in excess of 30 to 50 mbar and air admitted at a vacuum of 1 to 16 mbar. In addition, this prevents overfilling the fuel tank.
A check valve (71) in the purge line prevents the boost pressure building up toward the activated charcoal canister.

(United States of America)
During refueling the fuel vapors are collected additionally from the fuel tank and passed on to the activated charcoal filter (ORVR = Onboard Refueling Vapor Recovery). An activated charcoal canister of about 3 l capacity is used, with a connection for the ORVR vent line. The activated charcoal canister shutoff valve (Y58/4) and fuel tank pressure sensor (B4/3) are necessary for the checking the leaktightness.





Model from chassis no. A046659 (approx. 23.3.05), without (United States of America) and Model from chassis no. 469233 (approx. 23.3.05), without (United States of America) with ski bag (Code 282) or cooling compartment in rear backrest (Code 308) or with retrofitted additional vent valve (76/1)
75 Fuel tank
76 Vent valve (fitted as standard)
76/1 Vent valve (additional from series production break point or retrofitted)
77 Activated charcoal canister
N3/10 ME-SFI control unit
Y58/1 Purge control valve
A to the intake manifold
B Air admission
C Line to fuel tank
D Line to purge control valve

The additional vent valve (76/1) prevents vacuum pressure from the intake manifold from reaching the fuel tank via the activated charcoal canister when regeneration is activated. For this purpose, the valve closes as soon as a membrane is pressurized with vacuum pressure from the activated charcoal canister. If excess pressure or vacuum pressure affects the other valve connection, it opens immediately. Thus aeration and ventilation of the fuel tank is still possible without restriction via the standard vent valve (76).

Pay attention to the installation position of the vent valve (76/1).
Check aeration at the activated charcoal canister for contamination (e.g. dust, spider's webs).