Purge System With Leak Test, Function - GF47.30-P-3017MNH
Engine 176.9, 177.9 in model 463
as of model year 2019
with code ZU8 (National version for USA)
Schematic illustration of fuel tank
Purge system with leak test, general
As per the legal requirements no fuel vapors should escape into the environment. Therefore they are first stored in the fuel tank and in an activated charcoal canister. If the activated charcoal canister is fully loaded, the fuel vapors are suctioned at regular intervals out of the internal combustion engine and led to the combustion. The lawmaker also requires that the fuel tank is checked at the same intervals for leaktightness.
Function requirements for purge system with leak test
- Engine switched off
- Ambient temperature between 4 and 35°C
- Air pressure > 780 hPa (which means that no test takes place above an altitude of about 2500 meters)
- Fuel level in fuel tank between 15 and 85 %
- Battery voltage > 11 V
- Tank cap closed
- No fault at involved actuators or sensors
Purge system function sequence with leak test
The leak test of the purge system takes place in two stages (function chain) and must detect the following leaks:
- Leak equal to or greater than 1 mm dia.
- Leak equal to or greater than 0.5 mm dia.
The switchover valves for purging at the left and right must be closed here (switchover valves not actuated = purging blocked). Test sequence:
- Vehicle parked and ignition switched off.
- ME-SFI control unit enables diagnosis.
If the value of the current for the reference leak is exceeded during measurement, the fuel tank and its aeration and ventilation system are leaktight, otherwise a leak is present. The magnitude of the leak is recognized by the time the pump has to operate before a defined reference current is reached.
The pressure buildup also depends on the fuel level in fuel tank. If the tank cap (e.g. when fueling) is opened, the diagnosis is interrupted.
Any leaks detected, are stored in the fault memory of the ME-SFI [ME] control unit. After a fault occurs twice, the engine diagnosis indicator lamp lights up on the instrument cluster.
Schematic representation of purging
| Electrical function schematic for purge system with leak test | PE47.30-P-2053-97ZGF | ||
| Overview of system components for gasoline injection and ignition system with direct injection | GF07.70-P-9998MNH |