Purging system with leak test function - GF47.30-P-3016G
MODEL 463.237 up to 31.5.12 with ENGINE 273 with CODE (ZU8) USA version as of Model Year 2009/YoM 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 T < 45°C
- Coolant temperature for engine start <100°C
- Air injection not active
- Air pressure p >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 at the left tank half fuel level sensor (B4/1) or right tank half fuel level sensor (B4/2)
- No fault in the purge control valve
- Battery voltage U > 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 dia. ≥ 3 mm)
- Fine leak (leak dia. ≥ 1 mm)
- Very fine leak (leak dia. ≥ 0.5 mm)
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.
This vacuum is measured by the tank pressure sensor.
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 detects a system with a gross leak, the fuel reserve indicator lamp (A1e4) in the instrument cluster blinks and the message "CHECK FILLER CAP" appears in the multifunction display.
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. 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.
| Component description for ME-SFI [ME] control unit | N3/10 | GF07.61-P-6000G |