Test Groups WBMXV02.8M52 & WBMXV02.8Z35
General Description - Evaporative system monitoring permits detection of leaks in evaporative emission control system with a diameter of .039" (1 mm) and greater. Evaporative emission control system is hermetically sealed off from atmosphere by means of a shut-off valve at charcoal canister. When purge valve opens, engine generates a vacuum in tank. After closing purge valve, pressure increase is measured by a tank pressure sensor. If vacuum increases above a defined threshold, a leak is detected. As part of vacuum, check purge flow is verified.
Evaporative Purge System Flow Check (WBMXV02.8M52) - Purge flow from charcoal canister through purge valve is monitored after coolant temperature has reached a fixed minimum value. Diagnosis is started during regular purging.
Monitoring Process (WBMXV02.8M52) - See and Figure-Fig 4 .
- Step 1 - For Rich Or Lean Mixture: Flow through purge valve is assumed as soon as the lambda controller is compensating for a rich or a lean shift. After this procedure the diagnosis is completed and the evaporative purge system resumes working normally.
- Step 2 - For Stoichiometric Mixture Or Step 1 Fails: In this case, lambda controller does not need to compensate for a deviation. Therefore, after finishing regular purging, purge valve is opened and closed abruptly several times. Effect of additional cylinder charge triggers a variation of engine idle speed. If a predetermined value is reached, diagnosis procedure is completed.
- Step 3 - For Stoichiometric Mixture Or Step 2 Fails: If threshold at step 2 is not reached, an additional procedure is performed. Purge valve is opened and the idle air control valve simultaneously is closed to compensate idle speed increase. The effect is a decrease of measured idle air mass by mass airflow sensor. If a predetermined value is reached, diagnosis procedure is completed.