Purging system with leak test function - GF47.30-P-3016MMC

MODEL 216.3, 221.0/1 with ENGINE 157.9 with CODE (494) USA version

MODEL 216.3, 221.0/1 with ENGINE 278.9 with CODE (494) USA version

Fig 1: Purging System With Leak Test - Schematic Diagram

Courtesy of MERCEDES-BENZ USA

Schematic representation

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. 3 minutes) or self-adjustment of the mixture formation occurs
Lambda control enabled
Intake air temperature <72°C
Coolant temperature for engine start <100°C
Air injection not active
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 fuel tank at least 30%
No fault in the activated charcoal canister shutoff valve
No fault on the fuel level sensor, LH or RH tank half (B4/1, B4/2)
No fault in the purge control valve
Battery voltage > 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.)

Function sequence for purge system with leak test

The function sequence is subdivided into the following steps:

Function sequence for gross leak check
Function sequence for 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.

As result, a vacuum forms in the fuel tank, which is detected 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 IC (A1) is actuated by the chassis CAN (CAN E) and backbone CAN (CAN F) (the warning lamp flashes). The additional message "CHECK FILLER CAP" in the multifunction display (A1p13) is issued if fueling of > 20 l is recognized. Otherwise only the error "gross leak" is saved in the fault memory.

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).

Function sequence for fine leak check

A vacuum of about -15 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 for very fine leak check

If no minor leak has been detected, the purge system is briefly enabled and a vacuum of approx. -17 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. 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.

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 and the backbone CAN.

Electrical function diagram for system purging with leak test	Model 216	PE47.30-P-2051-97CAH
	Model 221	PE47.30-P-2051-97SAG
Overview of system components for gasoline injection and ignition system with direct injection		GF07.70-P-9998MMB