Evaporative Emissions System: Description and Operation

TANK VENTING SYSTEM:



Fuel vapor is collected in the carbon canister. This canister is mounted in the front, right-hand wheel arch.

The fuel vapor collected in the carbon canister is fed back into the combustion cycle. The carbon canister is purged with fresh air thus regenerating the carbon.

Function:



An electromagnetic valve (see arrow in image) is installed in the line between the intake housing and carbon canister. The flow direction of the one-way valve is imprinted on the plastic housing. The valve is secured below the intake pipe for cylinder 5.

The tank venting valve is clocked under map control with warm engine and active oxygen regulation. The resulting pulse duty factor is dependent on the airflow rate of the engine and the load density of the carbon canister. When the mixture drifts from lambda = 1 towards a rich or lean setting (caused by the purging of the carbon canister), this is detected by the control unit across the oxygen sensing system and is corrected by readjusting the mixture control during the tank venting phase. The first purging phase is performed after the engine is started and when the appropriate operating conditions are reached (engine temperature and oxygen regulation operations). It is ended by the DME control unit 250 seconds after the engine has been started. The mixture adaptation phase is then performed for 100 seconds. The next tank venting phase occurs, and so on.

Operation Of Tank Venting Valve
The tank venting valve is constructed in such a way that it is closed when the ignition is off.
If the ignition is switched on, the DME control unit applies a positive potential to the tank venting valve via terminal 54. When the engine is started and the operating conditions described previously are reached, the tank venting valve is once again connected to ground by the DME control unit, but via terminal 61, and opens. When the engine is switched off but the ignition switched on, the new Porsche System Tester 2 can be used to check that the valve is functioning correctly.