Purging system with leak test function - GF47.30-P-3016MIG

MODEL 251.054/154 with ENGINE 272.945 with CODE (494) USA version as of Model Year 2009/CY 08 

MODEL 164.186 with ENGINE 272.967 with CODE (494) USA version as of model year 2009/CY 08 model refinement package 

MODEL 164.156 with ENGINE 272.967 with CODE (494) USA version 

MODEL 251.056/065/156/165 with ENGINE 272.967 with CODE (494) USA version as of Model Year 2009/CY 08 

MODEL 164.871 with ENGINE 273.923 with CODE (494) USA version as of Model Year 2009/CY 08 

MODEL 164.172 with ENGINE 273.963 with CODE (494) USA version as of model year 2009/CY 08 model refinement package 

MODEL 164.886, 251.072/172 with ENGINE 273.963 with CODE (494) USA version as of Model Year 2009/CY 08 

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 in fuel level indicator sensors, LH or RH tank halves (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 dia.)
• Fine leak (leak the same or greater than a 1 mm dia.)
• Very fine leak (leak the same or greater than a 0.5 mm dia.)

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 switchover valve is opened. The vacuum in the intake manifold reaches the 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 build-up 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 dia.), 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 made 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 fine 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 fuel outgassing. 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 diagram for system purging with leak test	Model 164		PE47.30-P-2051-97MAA
		Model 251		PE47.30-P-2051-97RAA
	ME-SFI [ME] control unit, component description	N3/10	Engine 272	GF07.61-P-6000MIG
		N3/10	Engine 273	GF07.61-P-6000MLG