Purging System

With Code (494a) USA Version
With Code (808) Model Year 1998
With Code (809) Model Year 1999
With Code (800) Model Year 2000
220 with Engine 112, 113, 137 With Code (494a) USA Version
215 with Engine 137, With Code (494a) USA Version

Fuel Evaporation System Test


Task
The leak test of the evaporative emission control system must detect leaks as from approx. 1 mm and, with effect from model year 2000, as from approx. 0.5 mm diameter. Legislation requires that no fuel vapors pass to atmosphere.

Design Shown On Engine 119:

Function Diagram Legend:

Function
The leak test (function chain) is performed in several phases:
- 1. Coarse leak test
- 2. Fine leak test. approx. >= 1 mm diameter
- 3. with effect from model year 2000 in addition micro leak test.
approx. >= 0.5 mm diameter

Test requirements
- Vehicle stationary
- Engine idling
- Secondary air injection not active
- Disable time after engine start elapsed, approx. 16 minutes
- Fuel level between 1/4 and 3/4
- Low charge in activated charcoal canister
- If the fuel tank splashes excessively (impermissible pressure jumps), that is detected by the [1][2]fuel tank pressure sensor (B3/4) and the test ended

1. Coarse leak test
The activated charcoal canister shutoff valve (Y58/4) is closed and the purge control valves opened. The intake manifold vacuum flows to the fuel tank and is detected by the [1][2]fuel tank pressure sensor (B4/3).

If no build-up of vacuum takes place in the fuel tank or if approx. 7 mbar is not achieved within approx. 10 s, a major leak exists (e.g. fuel tank cap open, loose hose line).


NOTE: If the ME-SFI control module detects a major leak in the fuel system, the fuel reserve warning lamp in the instrument cluster flashes.


2. Fine leak test
If the coarse leak test has been completed without any fault, the fine leak test is performed. In this case, when the vacuum is achieved (approx. -7 mbar), the purge control valves (Y58/1, Y58/2 or Y58/3) are closed and the vacuum reduction is then assessed for about a further 30 seconds.

During this period the vacuum must remain practically constant or must reduce at the most only so rapidly as would be the case if there were a teak of approx. 1 mm diameter. If a major leakage exists the CHECK ENGINE malfunction indicator lamp (MIL) is actuated.

3. Micro leak test (as of model year 2000)
If the fine teak test is satisfactory, the micro leak test is then performed. In this case, the vacuum reduction is examined more closely. A leakage which equals a leak of approx. >= 5 mm diameter, results in a fault entry.
After completion of the test, the activated charcoal filter shutoff valve (Y58/4) is opened again.

Proper operation of the purge control valves is checked at the same time as they are actuated. In the case of engine 120 ME the purge control valves are actuated alternately.

Fuel level
The instrument cluster signals the fuel level to the ME-SFI control module (engine 120: N3/12). Only the coarse leak test is performed if the fuel level is below 1/4 or above 3/4.

Fuel tank position/design/function
- Model 210
- Model 129
- Model 140
- Model 170
- Model 203
- Model 202, 208
- Model 163
- Models 215, 220