Purging System With Leak Test Function - GF47.30-P-3016MNB
Engine 178.9 In Model 190
With Code 494 (USA version)
Schematic diagram
Purge system function requirements with leak test, general
- Engine at idle
- Vehicle stationary
- Gear range "D" or "R"
- Blocking time after Engine start elapsed (approx. 3 minutes) or self-adjustment of the mixture formation occurs.
- Lambda control released
- Intake air temperature <72°C
- Coolant temperature for Engine start <100°C
- 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 at least 30%
- No fault in the activated charcoal canister shutoff valve
- No fault on fuel tank fill level sensor, fuel level indicator, left (B4/1)
- No fault at left and right purging switchover valves
- Battery voltage > 11 V
Purge system with leak test, general
The legislator requires that no fuel vapors reaches the open air.
The leak test of the purge system must take place in three stages (function chain) and recognizes the following leak:
- Gross leak (a leak the same or greater than a 2.5 mm dia.)
- Fine leak (a leak the same or greater than a 1 mm dia.)
- Very fine leak (a 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-fine leak check
- Function sequence for gross leak-very fine leak check
Function sequence for gross leak-fine leak check
To check for a gross leak, the activated charcoal canister shutoff valve closes and the left and right purging switchover valve opens. The vacuum created in the intake air system reaches the fuel tank.
Vacuum then builds up in the fuel tank, and is measured by the fuel tank pressure sensor.
If no vacuum builds up in the fuel tank (approx.-6 mbar within approx. 12 s) there is a major leak (e.g. tank cap open, hose line loose). The test will be interrupted and the error "gross leak" stored in the fault memory.
If the ME-SFI [ME] control unit (N3/10) recognizes a gross leak system, the fuel reserve warning lamp (A1e4) is actuated (warning lamp flashes) via the drive train CAN (CAN C1), powertrain control unit (N127), chassis CAN 1 (CAN E1), electronic ignition lock control unit (N73), interior CAN (CAN B), AMG Gateway control unit (N93/9) and user interface CAN (CAN HMI) in the IC (A1).
The additional message "CHECK FILLER CAP" is output in the multifunction display (A1p13) if a refueling volume of > 25 l is detected. Otherwise only the error "gross leak" is saved in the fault memory.
While checking for fine leaks, a vacuum of about -6 mbar is built up again 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.
If no leak can be found, although a "gross leak" fault is indicated (if the leak diameter is more than 2.5 mm, there should be a loud hiss), replace the fuel tank pressure sensor.
Function sequence for gross leak-very fine leak check
If no "fine leak" has been detected, purging is briefly enabled and a vacuum of about -6 mbar is then 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 "very fine 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 fine and very fine leaks is aborted if an excessive lean correction of the lambda control takes place during the buildup of the vacuum.
The function of the left and right purging switchover valve is checked at the same time by means of actuation. If the closed switchover valves jam, the "Gross leak" fault is stored.
If faults are detected, these are stored in the fault memory by the ME-SFI [ME] control unit and the Engine diagnosis indicator lamp (A1e58) is actuated via the drive train CAN, powertrain control unit, chassis CAN 1, electronic ignition lock control unit, interior CAN, AMG Gateway control unit and the user interface CAN in the IC.
| Electrical function schematic for purge system with leak test | PE47.30-P-2051-97HBA | ||
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