Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
Technical Description: Purging: Notes
The illustration shows the system with vapor recycling (ORVR) and tank integrity diagnosis.
The fuel that evaporates in the tank passes through a pipe to the EVAP canister. The active charcoal in the EVAP canister will eventually become saturated as it absorbs the hydrocarbon vapor. When the engine is started, the surrounding air is drawn through the EVAP canister via a purge valve and a non return valve in the intake manifold. The petrol vapor is drawn with the air and burned in the engine. When the pressure in the intake manifold exceeds the atmospheric pressure, another non return valve opens and purging will now take place to the suction side of the turbocharger.
In an de-energized state, the purge valve is closed. It is supplied from the main relay and is controlled by a 16 Hz PWM from control module pin 27. If the tank integrity diagnosis is active, the frequency will be 8 Hz.
The pulse ratio regulates the flow so that it always constitutes a specific proportion of the total flow consumed by the engine.
If the air/fuel ratio in the flow deviates from 14.7:1, the closed loop will be affected. However, it is not the task of closed loop to correct for the excess caused by the purge so the purge has a correction factor that is affected by the closed loop as soon as the purge starts. The entire closed loop deviation from 1.00 is transferred to the purge correction factor, which means that closed loop fluctuates around 1.00 (0%) even if the purge contains large amounts of hydrocarbons or consists of pure air.
When purging is not active the factor 1.00 is used and the entire fuel fault is corrected by the closed loop along with the multiplicative and additive adaptation.
The limits for purge adaptation are 0.75 and 1.25 respectively.
The following conditions must be fulfilled before purging can be activated:
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.