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

MODEL 203 with ENGINE 113.988 with CODE (494) USA version

MODEL 209 with ENGINE 113.987 with CODE (494) USA version

MODEL 215 with ENGINE 113.986 with CODE (494) USA version

MODEL 220 with ENGINE 113.986 with CODE (494) USA version

Fig 1: Purge System Function Diagram - Type 171 (With Leak Test)

Fig 2: Purge System Function Diagram - Model 203, 209 (With Leak Test)

Fig 3: Purge System Function Diagram - Model 215, 220 (With Leak Test)

The US legislature requires that the fuel vapors are not released into the atmosphere.

The leak test for the fuel evaporation control system must detect leaks with a diameter of over 0.5 mm and must take place in three stages (function chain):

Test for major leaks (equal to or greater than 3 mm)
Test for a fine leaks (equal to or greater than 1 mm)
Test for micro-leaks (equal to or greater than 0.5 mm)

Test for major leaks

The activated charcoal canister shut-off valve (Y58/4) is closed and the purge control valve (Y58/1) opened. The vacuum in the intake manifold reaches the fuel tank (75).

A vacuum builds up 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 (about -6 mbar within about 12 seconds) then there is a gross leak (for example a filler cap is open or a hose is loose).

The test will be interrupted and the error gross leak will be registered.

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

Test for a minor leak

The purge control valve is closed at a vacuum of around -6 mbar. The system is closed and thereby air-sealed. The vacuum is them measured for approx. 30 seconds. The vacuum must not reduce any faster than 0.3 to 0.5 mbar per second (depending on the level of fuel in the tank). If the vacuum drops more rapidly, there is a minor leak. The test will be interrupted and the error fine leak will be registered.

Check for micro leakage

If no minor leak has been detected, the purge system is briefly enabled and a vacuum of approx. - 6 mbar is built up again. The vacuum level not reduce any faster than 0.1 to 0.15 mbar per second (depending on fuel level in the tank) when the system is closed.

If the vacuum reduces more rapidly, then the error "micro leak" fault is registered.

Vacuum forming depends on the fill level in the fuel tank and the vapor emissions from the fuel. Vapor emissions from the fuel are measured shortly before the test by the tank pressure sensor and are taken into account in evaluating the fault.

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

Test requirements

Engine at idling speed
Vehicle stationary
Drive position "D" or "R" is engaged
Blocking time after starting the engine has lapsed (around 16 minutes) or mixture adaptation has occurred
Lambda control enabled
Intake air temperature <45°C
Coolant temperature at engine start <100°C
Air injection not active
Air pressure >780 hPa (that means that no test is performed above a height of around 2500 meters)
Low charge in the activated charcoal canister (77)
Fuel level in the fuel tank between approximately 1/4 and 3/4
No fault in the activated charcoal canister shut-off valve
No fault in the fuel tank pressure sensor
No fault in the purge control valve
Battery voltage >11 V

The test for minor and micro leaks is aborted if excessive lean correction by the lambda control takes place during the build-up 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.

The tests are not stopped if there is an implausible fuel level resulting from a defective fuel level sensor (B4, B4/1, B4/2).

If no leak for the fault major leak is found (there is a clear hissing noise if there is a leak of more than 3 mm), replace fuel tank pressure sensor. The fuel tank pressure sensor may have a fault which results in a signal which is constant but still plausible (sensor sticking).

Component description for the ME-SFI [ME] control unit	N3/10		GF07.61-P-6000SM
Component description for the fuel tank	75	Model 171	GF47.10-P-2000VS
	75	Models 203, 209	GF47.10-P-2000PS
	75	Models 215, 220	GF47.10-P-2000MS
Component description for the activated charcoal canister	77		GF47.30-P-2010SM
Component description for purge control valve	Y58/1		GF47.30-P-2020SM
Component description for the fuel tank pressure sensor	B4/3		GF47.30-P-2100SM
Component description for the activated charcoal filter shutoff valve	Y58/4		GF47.31-P-2100SM