Purge System With Leak Test, Function - GF47.30-S-3017TRC
Engine 274 in model 447, 448
Purge system function requirements with leak test, general
- Engine at idle
- Vehicle stationary
- Blocking time after engine start elapsed or self-adjustment of the mixture formation occurs
- Lambda control released
- Intake air temperature <72°C
- Coolant temperature <100°C
- Air pressure >780 hPa (which means that no leak test takes place above an altitude of about 2500 meters)
- Low charge in the activated charcoal canister (1)
- Fuel level in the fuel tank (3) is at least 30%
- No error in the FSCU (FSCU) (N118) and in the drive train CAN (CAN C)
- No fault in the purging switchover valve (Y587)
- On-board electrical system 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 therefore recognizes the following leak:
- Gross leak (≥ 2.5 mm dia)
- Fine leak (≥ 1 mm dia.)
- Very fine leak (≥ 0.5 mm dia.)
Purge system with leak test, function sequence
The function sequence is subdivided into the following steps:
- Leak test for a gross leak
- Leak test for a fine leak
- Leak test for a very fine leak
Leak test for a gross leak
When leak testing for a gross leak, the purging switchover valve (Y58/7) opens. The vacuum in the intake manifold reaches the fuel tank (3). In this way a vacuum (about -6 mbar within 12 s) builds up in fuel tank (3).
Upon reaching the specified value the leak test for a fine leak is continued.
If no build up of vacuum occurs in the fuel tank (3), there is a gross leak present (e.g. tank cap open, purge line (6) defective). The leak test is broken and the error "gross leak" is stored.
Leak test for a fine leak
For the leak test on fine leak a vacuum is built up by about -6 mbar and closes the system airproof. Finally the vacuum is evaluated for about 30 s and may only reduce by a maximum of 0.3 to 0.5 mbar/s (dependent on fuel level).
Upon reaching the specified value the leak test for a very fine leak is continued.
If the vacuum drops more rapidly, there is a fine leak. The leak test is broken off and the error "fine leak" is stored.
Leak test for a very fine leak
If no "fine leak" has been detected, purging is enabled for a few seconds 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 dissipates more rapidly, the "very fine leak" fault is stored.
For recognized errors this is stored by the ME-SFI [ME] control unit (N3/34). Furthermore the request for actuation of the engine diagnosis indicator lamp (A1/1e58) is sent to the IC control unit (IC) (A1/1) via the chassis CAN (CAN E).
| Electrical function schematic for purge system with leak test | Engine 274 in model 448 | PE47.30-S-2053-97VDC | |
| Engine 274 in model 447 except code XM0 (Facelift) | PE47.30-S-2053-97TRC | ||
| Overview of system components for gasoline injection and ignition system with direct injection | Engine 274 in model 447, 448 except code XM0 (Facelift) | GF07.70-S-9998TRC | |
| Engine 274 in model 447.6/7 with code XM0 (Facelift) | GF07.70-S-9998TRJ |