GF47.30-P-3016MAW Purging System With Leak Test Function
GF47.30-P-3016MAW Purging System With Leak Test Function
- MODEL 204.0 /2, 212.0 /2 with ENGINE 156.9
- with CODE (494) USA version
Schematic representation
1 Activated charcoal canister chamber 1
2 Activated charcoal canister chamber 2
3 Activated charcoal canister chamber 3
45 Fuel filler neck
58 Fluid reservoir
75 Fuel tank
75/1 Fueling, limiting and vent valve
75/2 Breather valve
77 Activated charcoal canister
B4/3 Fuel tank pressure sensor
Y58/1 Purge control valve
Y58/4 Activated charcoal filter shutoff valve
A Air admission line and vent line
B Purge line
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 less than 45°C
- Coolant temperature for engine start less than 100°C
- Air injection not active
- Air pressure greater than 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 in the activated charcoal canister shutoff valve
- No error in LH or RH fuel level indicator sensor (B4/1, B4/2)
- No fault in the purge control valve
- Battery voltage greater than 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:
- Function sequence for gross leak check
- Function sequence fine leak check
- Function sequence for very fine leak check
Function sequence for gross leak check
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.
Vacuum then builds up in the fuel tank, and is measured 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 gross leak in the system the fuel reserve warning lamp (A1e4) in the instrument cluster (A1) is actuated via the chassis CAN (CAN E) (warning lamp flashes). The message "CHECK FILLER CAP" is also shown in the multifunction display (A1p13).
If no leak can be found, although a "gross leak" fault is indicated (if the leak diameter is more than 3 mm, there should be a loud hiss), replace the fuel tank pressure sensor. The fuel tank pressure sensor may be faulty to the extent that the signal remains constant and plausible (sensor sticking).
Function sequence for fine leak check
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.
Function sequence very fine leak check
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. Fuel outgassing is measured shortly before fuel tank pressure sensor is checked, and taken into account for fault indication.
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.
If there are faults recognized then these are stored by the ME-SFI [ME] control unit in the fault memory and the engine diagnosis indicator lamp (A1e58) is actuated in the instrument cluster via the chassis CAN.
