rcrone928

After 100 mile drive to phoenix in my 83 928 I noticed the fuel door was pushed open about 1/4 in. When opening gas cap it took 1/2 min for the pressure to drop along with loud wooshing noise. Is it possible that the vent to the tank is plugged? Thanks in advance.

Speedtoys

Vent solenoid at the front of the motor not opening?

http://www.autoatlanta.com/porsche-p...section=201-10

#18 ??

rcrone928

thanks speed toys for the reply. I'm not sure what that is. Could it be the vac operated valve mounted on the passenger side on the fender lip?

Speedtoys

Chase down the lines that go to that thing..and make sure the vacuum line is still on it I guess.

A more experienced person on the older cars may chine in as well. On an S4, that's usually the issue. The purge valve.

rcrone928

I think I follow what you are saying. doesn't that valve purge the charcoal canister?

Speedtoys

Which is connected to the....

James Bailey

There is a breather plumbed into the tank with a one way check valve ..allows it to inhale but not exhale. the PET parts diagrams will help you understand. The fuel pump was collapsing the fuel tank as the gallons of gas were not being replaced with air....
The purging valve for the charcoal can is different on early vs S-4 . Early uses a thermo switch rather than electric solenoid. In normal operation when it opens it pulls a small amount of air out of the tank which is replaced by the venting mentioned above. This fresh air purges any vapors from the charcoal can.

You need the PET showing the gas tank and overflow reservoir etc. in the rear.....

rcrone928

I think I follow what you are saying Mr. Baily but my fuel tank was inflated like a balloon, like it's being pressurized.

Randy V

Take a look at the gas tank (it is plastic). My bet is that it is imploded somewhat due to the vacuum applied to it.

rcrone928

Randy V. I take off the gas off cap and gas fumes come out in a rush just like the tank is under pressure and not under a vacuum. I guess what I'm asking is if this is normal? I know this is a sealed system and all it seems excessive.

Speedtoys

The link I pasted will get him there too.

Havent needed PET .

Randy V

Ah, that is not common.

Speedtoys

Vapor pressure.

That charcoal canister valve up front working ok?

rcrone928

Speedtoys. do you mean the adjustable control valve going to the intake or the plastic diaphram unit back by the washer bottle? how would I test proper operation? Thanks for your help.