Fuel tank evap/purge valve - how to test

[chazsandiego]

My GFs 535i has some issues starting without the pedal depressed and it will sometimes die at idle. Just checking hoses and such I decided to test the fuel tank purge valve. I haven't been able to find a spec for the proper resistance. Does anyone happen to know off hand?

Thanks!

[shogun]

For a quick test: the tank breather valve should have a resistance of 45 +/- 20 Ohm and it closed without 12V power.

German description from the BMW testing instructions for M1.1: Pruefanleitung DME 1.1:
Tankentlueftungsventil (TE-Ventil) pruefen: Das TE-Ventil wird im Sekundentakt angesteuert. Die Taktung ist mit der Hand fuehlbar.
Dichtheit pruefen: Unterdruckversorgung vom vom Service-Tester am 8-mm Anschluss anschliessen (Durchflusspfeil beachten). Unterdruck auf 600 mbar einregulieren und TE-Ventil mit 12V versorgen. Unterdruckpumpe abschalten, nach 20 Sekunden darf der Druckabfall 50 mbar nicht uebersteigen. Im stromlosen Zustand ist das TE-Ventil durch ein Rueckschlagventil bis zu einem Saugrohrunterdruck von 20 mbar geschlossen.
Ansteuerphasen pruefen: Das TE-Ventil wird im Leerlauf angesteuert (Anzeige EIN) und ist somit geschlossen. Sobald die Lambdaregelung aktiv ist und die Drehzahl bis ca. 1600 UPM erhoeht wird, kann die schrittweise Oeffnung beobachtet werden (Anzeige AUS).

translated: From test instructions DME 1.1:
Tank venting valve (TE valve) check: The TE ( TE = Tank Entlueftung = tank breather valve) valve is activated every second. The clicking one can feel by touching the valve by hand.

Check tightness: Connect the vacuum supply from the service tester to the 8-mm connection (observe flow arrow). Adjust negative pressure to 600 mbar and supply TE valve with 12V.
Switch off vacuum pump, after 20 seconds the pressure drop may not exceed 50 mbar.
In powerless state the TE valve is closed by a check valve up to a suction pipe vacuum of 20 mbar.

Check driving phases:
The TE valve is activated in idle (display ON) and is thus closed. As soon as the lambda control is active and the speed is increased up to approx. 1600 rpm, the stepwise opening can be observed (display OFF).

[chazsandiego]

Very cool, I'm sitting at 48.

Thanks for that Shogun!

[shogun]

check the hoses of the fuel tank breather valve system.
Often they are brittle and then the engine sucks uncontrolled air = bad cold start.
Under normal condition of a cold start the breather valve is closed. As soon as the lambda control is active = the cat has reached the required temperature and the speed is increased up to approx. 1600 rpm, then the step by step opening can be noticed.