Purging function - GF47.30-P-3015MMO

MODEL 212.095 with ENGINE 276.9 up to model year 2014 

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

Fig 1: Fuel Tank Aeration And Ventilation Schematic Diagram (Except Code 494 USA Version)

Courtesy of MERCEDES-BENZ USA

Purging function requirements, general points 

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

The function requirements "internal combustion engine running" includes all function sequences of the fuel low pressure and high-pressure circuit, as described in the function "fuel supply".

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)
• Intake air temperature sensor (B17)
• Intake manifold intake air temperature sensor (B17/1)
• Pressure sensor downstream of throttle valve (B28/7), engine load
• Crankshaft Hall sensor (B70), engine speed
• Left and right oxygen sensor elements upstream of catalytic converter (G3/3b1, G3/4b1)

Function sequence for purging 

Ventilation of the fuel tank (operational ventilation) takes place over the aeration/vent valves, the aeration/vent lines and the activated charcoal canister.

When this is done, the fuel vapors flow into the activated charcoal canister where they are stored, and from where they are passed into the intake manifold 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 according to the level of fuel vapor charge in the activated charcoal canister.