Purging function - GF47.30-P-3015G

MODEL 463.202/222/236/237 up to 31.5.12 with ENGINE 273 as of Model Year 2009/YoM 08 

Fig 1: Identifying Purging Function Diagram

Courtesy of MERCEDES-BENZ USA

Purging function requirements, general 

• Circuit 87M ON (engine control ON)
• Engine start before t > 45 s
• Coolant temperature T > 40°C
• Engine not in deceleration mode
• Engine not in the lambda adaptation phase

Purging, general 

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 purging, the ME-SFI [ME] control unit reads the following sensors:

• Hot film MAF sensor, engine load
• Intake air temperature sensor
• Coolant temperature sensor
• Crankshaft Hall sensor, engine speed
• LH and RH O₂ sensors upstream of catalytic converter, oxygen sensor signals

Purging function sequence 

The fuel tank is ventilated through the safety valve (rollover valve), the aeration/vent line and the activated charcoal canister. The fuel vapors flow to the activated charcoal canister where they are stored, and drawn off into the variable 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 purge control valve and combusted in the engine.

To control the purging quantity, the ME-SFI [ME] control unit actuates the purging switchover valve at the ground end using a pulse width modulated signal (at a frequency of 10 Hz).

The purge quantity is determined by continuously opening and closing the purge control valve with on-times of varying duration.

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.