Fuel pressure on GTi

[Joniboy]

Hi guys,

I did a quick search but couldn't find any info on this.

Is it normal for the fuel cap to hiss when you take it off?
Mine does it as soon as I start to release it and continues until the cap is fully unscrewed. It sounds like a bottle of coke being opened after being shaken about.
Is it normal to have this amount of pressure in there?
None of my previous cars has ever done this so I'm a little concerned.

Any pointers would be grand.

Cheers,

Jon

[Mouse_GTI]

Never heard mine do that

[tegwin]

Its normal....


On larger fuel tanks....especially diesel ones you have to open the cap very carefully so you equalise the pressure....



Provided you can fill the car ok and it runs ok... I would not worry atall

[Tim_GTi]

I've never experienced this myself either

[Joniboy]

I'm wondering if the breather could be blocked?
I filled up again last night and sure enough on undoing the cap it started hissing really loudly. It does'nt seem to matter if the tank is full or near empty, it always hisses when you undo the cap.
It doesn't seem to affect the running so I'm not too worried but it does seem odd.

As for the big tank suggestion - my Corrado has a huge capacity tank (70 litres) and has never done this and none of my other cars have done it.
I guess I best get out there on Boxing day and have a poke around

[bbspolo]

Been scraching my head about this one but as far as i can think there shouldnt be any (or very little) pressure in your fuel tank???
i would advise checking your pump and make sure it isnt damaged in anyway causing it not only 2 presureise the fuel lines but also the tank?
Another idear is checking the return fead 2 the takn as this should only have very little pressure behind it??
It strange how u say it runs fine as ither of these i would have though would have had a affect on how the engine runs??

When i see some work mates of mine ill put it 2 them for u see if they can come up with any better diagnosis for you!

[bbspolo]

only time i have had it hiss has been when the tank is very empty and the breather is blocked as then the hiss isnt pressure in the tank its a vacume in the tank!! And the hiss is air rushing in????
but since u have said it does it all the time (not mattering how much fuel it has) kinda blows that sujestion out the water???

[Joniboy]

lol - i've only just seen this - sorry mate. and thanks for the help.

It still makes that noise but as you say it is actually sucking the air in - you can feel it when you take the cap off.
Still runs ok though.

The breather seems ok and so do the return lines. I'm gonna get the pump checked next.

Cheers,

Jon

[Joniboy]

Just to put an end to this thread, I finally found the answer to the pressure issue.
As suggested it wasn't pressure escaping but rather air being sucked into the tank when opening the cap. It was so fast it even whistled a bit.

Anyway, on inspection, the return breather from the charcoal canister to the fuel tank had a nasty kink in it. As soon as I took the kink out you could here the tank popping a little bit as the pressure equalised.

I've replaced that bit of pipe so I'll keep an eye on it and see how it goes.

Cheers for your help,

Jon