Purging function - GF47.30-P-3015MMA

ENGINE 157.9 in MODEL 212, 218

ENGINE 276.8 in MODEL 207, 212 as of model year 2014

ENGINE 276.8 in MODEL 218 as of model year 2015

ENGINE 278.9 in MODEL 207, 212, 218

Fig 1: Purging Function Diagram

Courtesy of MERCEDES-BENZ USA

Schematic diagram of fuel tank aeration and ventilation (except code 494 (USA version))

Purging function requirements, general points

Circuit 87M (engine timing ON)
Engine started for at least 60 to 80 s
Coolant temperature > 40°C
Engine not in deceleration mode
Engine not in the lambda adaptation phase

Purging, general points

When the fuel tank is being ventilated, no fuel vapors should escape into the outside air.

The fuel vapors are stored in the activated charcoal canister and burnt later in the engine.

In order to enable the purging, the ME-SFI [ME] control unit (N3/10) reads in the following sensors:

Coolant temperature sensor (B11/4) (model 207, 212), coolant temperature sensor (B11/4) (model 218)
Charge air temperature sensor (B17/8)
Pressure sensor downstream of throttle valve (B28/7), engine load
Crankshaft Hall sensor (B70), engine rpm
Left and right oxygen sensors upstream of catalytic converter (G3/3, G3/4)

Ventilation of the fuel tank (operational ventilation) takes place over the aeration/vent valves, the aeration/vent lines and the activated charcoal canister. The fuel vapors flow to the activated charcoal canister where they are stored and drawn off into the charge air distributor when purging is enabled. When the engine is running, the fuel vapors stored in the activated charcoal canister are drawn off through the purging switchover valve and combusted in the engine.

The purging switchover valve is actuated by the ME-SFI [ME] control unit at the ground end to regulate the purging quantity by means of an electric signal between 0 and 500 mA. The purging quantity is determined through regulation of the opening cross-section of the purging switchover valve.

The idle speed control prevents the purging from causing a change in rpm when the engine is at idle. The fuel/air mixture is leaned out depending on the level of fuel vapors load in the activated charcoal canister.

Function sequence for purging

The purging is described in the following points:

Function sequence for partial load purging
Function sequence for wide open throttle purging (only for engine 276.8)

Function sequence for partial load purging

In partial load operation, the fuel vapors stored in the activated charcoal canister are drawn off by the existing vacuum through the purging switchover valve, the partial load operation check valve and the partial load vent line downstream of the throttle valve before being combusted in the engine.

Function sequence for wide open throttle purging (only for engine 276.8)

Charging induces an overpressure downstream of the throttle valve in wide open throttle operation which prevents any extraction of the fuel vapors through the partial load vent line. The partial load operation check valve prevents any pressure buildup in the direction of the activated charcoal canister.

If an overpressure occurs in wide open throttle operation, the fuel vapors are extracted over the wide open throttle operation check valve and the wide open throttle vent line. The vacuum required for this is generated by a Venturi nozzle. The fuel vapors are then routed over the wide open throttle vent line, turbocharger and the charge air cooler to the charge air distributor.

To check whether the wide open throttle purging can be enabled, the purging switchover valve is opened suddenly three times in succession. Pressure peaks of > 120 mbar must be registered here. For code 494 USA version the purging pressure sensor (B4/4) records the given pressure conditions in the wide open throttle purge line, and forwards a signal to the ME-SFI [ME] control unit.

Schematic diagram of the wide open throttle purging

Fig 2: Fuel Tank Aeration And Ventilation Schematic Diagram

Courtesy of MERCEDES-BENZ USA

Electrical function schematic for purge control	MODEL 207	PE47.30-P-2052-97EAI
	MODEL 212	PE47.30-P-2052-97DAK
	MODEL 218	PE47.30-P-2052-97XAC
Overview of system components for gasoline injection and ignition system with direct injection	ENGINE 157.9 in MODEL 212, 218 ENGINE 278.9 in MODEL 207, 212, 218	GF07.70-P-9998MM
	ENGINE 276.8 in MODEL 207, 212 as of model year 2014 ENGINE 276.8 in MODEL 218 as of model year 2015	GF07.70-P-9998MMP