Purge function - GF47.30-P-3015MOS

MODEL 216.376, 221.176 with ENGINE 275.953 as of Model Year 09/AEJ 08

MODEL 216.379, 221.179 with ENGINE 275.982 as of Model Year 09/AEJ 08

Schematic diagram of fuel tank aeration and ventilation

Fig 1: Fuel Tank Aeration And Ventilation Schematic Diagram

Courtesy of MERCEDES-BENZ USA

Purging function requirements, general

Circuit 87M ON (engine control ON)
Engine started for at least 45 s
Coolant temperature > 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 the purging, the ME-SFI control unit (N3/10) reads the following sensors:

Coolant temperature sensor (B11/4)
Charge air temperature sensor (B17/8) and pressure sensor downstream of throttle valve actuator (B28/7), engine load
LH and RH O₂ sensors upstream of CAT, oxygen sensor signals
Crankshaft position sensor (L5), motor speed

Purging function sequence

The fuel tank is ventilated through the safety valves (rollover valves), the fuel retention valve 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 purge control valve (Y58/1) and combusted in the engine.

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

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

The idle speed control prevents the purging from causing a change in rpm when the engine is at idle. A leaner fuel-air mixture is produced in line with the charge of the activated charcoal canister with the fuel vapors.

Electrical function diagram for purging function	Model 216	PE47.30-P-2052-97CAA
Electrical function diagram for purging function	Model 221	PE47.30-P-2052-97SAA
ME-SFI [ME] control unit, component description	N3/10	GF07.61-P-6000MOS