Purge system with leak test function - GF47.30-P-3016MAS

MODEL 216.377, 221.077/177 with ENGINE 156.984

as of Model Year 09/AEJ 08

with CODE (494) USA version

Schematic diagram of fuel tank aeration and ventilation

Fig 1: Identifying Fuel Tank Aeration And Ventilation Schematic Diagram

Courtesy of MERCEDES-BENZ USA

Function requirements for system purging with leak test

Engine at idle
Vehicle stationary
Gear range "D" or "R"
Blocking time after engine start elapsed (approx. 16 minutes) or self-adjustment of the mixture formation occurs
Lambda control enabled
Intake air temperature < 45°C
Coolant temperature for engine start < 100°C
Air injection not active
Air pressure >780 hPa (which means that no test takes place above an altitude of about 2500 meters)
Low loading of activated charcoal canister
Fuel level in the fuel tank between approximately 1/4 and 3/4
No fault at activated charcoal filter shutoff valve (Y58/4)
No fault on the fuel level sensor, tank half on the left or right (B4/1, B4/2)
No fault in the purge switchover valve (Y58/1)
Battery voltage > 11 V

Purge system with leak test, general points

The legislator requires that no fuel vapors reaches the open air. The leak test for the fuel evaporation control system must take place in three stages (function chain) and recognizes the following leak:

Gross leak (leak the same or greater than a 3 mm Ø)
Fine leak (leak the same or greater than a 1 mm Ø)
Very fine leak (leak the same or greater than a 0.5 mm Ø)

Purge system with leak test function sequence

The function sequence is subdivided into the following steps:

Gross leak check function sequence
Fine leak check function sequence
Very fine leak check function sequence

Gross leak check function sequence

The activated charcoal canister shutoff valve is closed and the purge control valve opened. Intake manifold vacuum present in fuel tank.

As result, a vacuum forms in the fuel tank, which is detected by the fuel tank pressure sensor (B4/3).

If there is no vacuum buildup in the fuel tank

(approx. -6 mbar within approx. 12 seconds) there is a major leak (e.g. tank cap open, hose line loose)

The test will be interrupted and the error "major leak" stored in the fault memory.

If the ME-SFI [ME] control unit (N3/10) detects a system with a substantial major leak, the fuel reserve warning lamp (A1e4) in the instrument cluster (A1) blinks and the message "CHECK FILLER CAP" appears in the multifunction display (A1p13).

If no leak for the fault major leak is found (there is a clear hissing noise if there is a leak of more than a 3 mm Ø), replace fuel tank pressure sensor. The fuel tank pressure sensor may be so faulty that the signal is constant but plausible (sensor sticking).

Fine leak check function sequence

A vacuum of about -6 mbar is built up and the system is closed airproof. The vacuum is them measured for approx. 30 seconds. The vacuum must not reduce more rapidly than 0.3 to 0.5 mbar per second (depends on fuel level). If the vacuum drops more rapidly, there is a minor leak.

The test will be interrupted and the error "fine leak" is stored.

Very fine leak check function sequence

If no minor leak has been detected, the purge system is briefly enabled and a vacuum of approx. -6 mbar is built up again. In a closed system, the vacuum must not drop faster than 0.10 to 0.15 mbar per second (depending on fuel level).

If the vacuum builds up more rapidly, the "micro leak" fault is stored.

The reduction in vacuum depends on the fuel level in the fuel tank and on degassing of the fuel. The degassing of the fuel is measured for a short time prior to the test by the fuel tank pressure sensor and is allowed for in the fault statement.

The activated charcoal canister shutoff valve is reopened after the tests.

The test for minor and micro leaks is aborted if an excessive lean correction of the lambda control takes place during the buildup of the vacuum.

The function of the purge control valve is checked at the same time by the activation. If the closed switchover valve jams, the "major leak" fault is stored.

Electrical function schematic for system purging with leak test	Model 216	PE47.30-P-2051-97CAC
	Model 221	PE47.30-P-2051-97SAC
ME-SFI [ME] control unit, component description	N3/10	GF07.61-P-6000MAS