whoooing noise around filler cap when i turn the ignotion off

[marksawtell]

Slowly working through the problems on my porsche 996 1999 c2!

My latest problem solving exercise is to stop the noise I can hear which is sometimes rev related and also when i turn the engine off, i hear a whooing noise (like a low octave flute) coming from around the fuel filler cap area.

Germansportscarspares suggested it might be the EVAP valve by the fuel filler. I replaced this and the plastic pipe that goes to the black box from the evap valve (i think this is called a charcoal cannister) and have noticed the sound hasnt gone away.

Not sure if its related but the engine can start to hunt if caught in traffic and sometimes stall and again i was advised this could be related to something on the evap system as the evap system adjusts mixture and throttle.

Anybody had this problem or got any suggestions?

As usual many thanks in advance for any help :0)

regards

mark

[wyovino]

(Removed by author)

Edited April 28, 2012 by wyovino

[JFP in PA]

Hopefully some more tech-savvy people will chime in here. If suction makes it difficult to remove the oil filler cap while the engine is running, it could indicate that your Air Oil Separator is bad.

He is talking about the gas filler cap, not the oil cap, which is an EVAP system related issue, which is usually a vacuum leak and why he is seeing stumbling issues when driving.

[marksawtell]

Thanks jfp, seeing as I've changed the fuel tank end do you think its worth changing the valve at the engine end? I've got durametric and it's not throwing up any error codes ..

[JFP in PA]

The valve at the engine end is more of a check valve than an operational valve (it has no electrical connections); I think you need to look more closely at the EVAP canister end. One thing you can do is hook the car up to a PIWIS or Durametric system and cycle the various valves at the canister end to make sure they are functioning.

Have you also checked the seal on the gas cap? They do fail and cause noise as well.

Edited April 27, 2012 by JFP in PA

[wyovino]

Doh! I have to learn how to read. Sorry.

[marksawtell]

Heres something intersting JFP....

UK cars do have a valve on the evap system close to the throttle body with electrical connections. I took a gamble and changed it and the strange noise from around the filler cap is no more :0)