Purging, Basic Function - GF47.30-P-1000A
Engine 139, 176, 177, 254, 256, 260, 264, 274, 279, 282
Overview
This document contains information on:
- General
- Function requirements
- Function
- Purging, general points
- Wide open throttle purging
- Partial load purging
- Purging when idling
General
When the fuel tank is being ventilated, fuel vapors escape. These must not get into the outside air. The arising vapors are temporarily stored in the activated charcoal canister and subsequently supplied to the combustion process. In order to prevent the activated charcoal canister being overloaded with fuel vapors, a regular purge is necessary.
Schematic diagram of fuel tank aeration and ventilation
Function requirements
- Engine management ON (circuit 87M)
- Engine start before at least 60 to 80 s
- Coolant temperature > 40°C
- Engine not in overrun mode
- Engine not in the lambda adaptation phase
Function
Purging, general points
The fuel tank is ventilated via the vent and bleed valves, the vent and bleed lines, and the activated charcoal canister.
The fuel vapors flow to the activated charcoal canister via vent and bleed lines. The fuel vapors are absorbed by the activated charcoal in the activated charcoal canister, and, when purging is initiated by the combustion engine control unit, they are extracted into the charge-air distributor and finally fed into the combustion process.
The vacuum in the charge-air distributor is used to extract the fuel vapors in the charge-air distributor. To regulate the regeneration quantity, the purging switchover valve is actuated at the ground end by a pulse width modulated signal by the combustion engine control unit. The purge quantity is determined by constantly opening and closing the purging switchover valve with on-times of varying durations.
The purging pressure sensor is not used to control the purge process, but is integrated in the circuit to monitor leakage. The use of the purging pressure sensor is country-dependent.
Wide open throttle purging
In full-load operation, the fuel vapors stored in the activated charcoal canister are suctioned out via the full-load operation check valve and fed to the intake air system upstream of the exhaust gas turbocharger. The required vacuum is generated by the Venturi nozzle. The exhaust gas turbocharger sucks in the gases stored in the activated charcoal filter together with fresh air and makes them available to the engine for the combustion process via the wide open throttle valve. The idle check valve is closed during this process.
In full-load operation, boost pressure is present in the intake air system and exceeds atmospheric pressure.
Schematic diagram of the wide open throttle purging
Partial load purging
In partial-load operation, depending on the throttle valve position and the pressure conditions in the intake air system, the gases stored by the activated charcoal filter are made available to the combustion engine for the combustion process via the full-load purge line and/or the partial-load purge line.
If there is a risk that, due to the currently prevailing pressure ratios, gases may flow into the idle mode purge line through the check valve, the idle mode purge line closes and the purging takes place exclusively via the full-load purge line.
Schematic diagram of wide open throttle purging
Purging when idling
In idle mode, the fuel vapors stored in the activated charcoal canister are extracted by the existing vacuum through the purging switchover valve, the idle mode check valve, and the idle mode purge line behind the throttle valve. The fuel vapors are then fed into the engine for the combustion process.
In idle operation, the boost pressure in the charge air system is almost equal to atmospheric pressure; there is a vacuum in the intake manifold (downstream of the throttle valve).
The idle speed control prevents the purging from causing a change in rpm when the engine is idle. The fuel/air mixture is leaned out appropriately depending on the load condition of the activated charcoal canister.
Schematic diagram of idle purging
| Function schematics | |||
| Function schematic for purging | Engine 282 in model 118, 177, 247 | PE47.30-P-2500-97A | |
| Engine 260 in model 118, 177, 247 Engine 264 in model 167 | PE47.30-P-2500-97B | ||
| Engine 256 in model 167 Engine 256 in model 213, 238 as of model year 2021 Engine 264 in model 213, 238, 257 as of model year 2021 | PE47.30-P-2500-97C | ||
| Engine 176, 177 in model 167 Engine 177.8 in model 290 | PE47.30-P-2500-97D | ||
| Engine 139 in model 118, 177, 247 | PE47.30-P-2500-97E | ||
| Engine 176, 256, 279 in model 223 | PE47.30-P-2500-97F | ||
| Engine 139 in model 206, 232 | PE47.30-P-2500-97G | ||
| Engine 177.8 in model 223, 232 | PE47.30-P-2500-97H | ||
| Engine 254 in model 206 | PE47.30-P-2500-97I | ||
| Engine 274 in model 213 as of model year 2021 | PE47.30-P-2500-97J | ||
| Additional basic functions | |||
| Purging pressure sensor, basic function | GF47.30-P-2000A | ||
| Detailed information | |||
| Purge system with leak test, detailed information | Engine 139, 176, 177, 254, 256, 260, 264, 274, 279, 282 in model all with code 460 (Canada version) Engine 139, 176, 177, 254, 256, 260, 264, 274, 279, 282 in model all with code 494 (US version) Engine 139, 176, 177, 254, 256, 260, 264, 274, 279, 282 in model all with code 830 (China version) Engine 139, 176, 177, 254, 256, 260, 264, 274, 279, 282 in model all with code 835 (South Korea version) |
GF47.30-P-1100B |