HELP fuel tank pressurising BIG TIME!!!

Hi all,
Just wondering if anyone could shed any light on this VERY annoying problem.
Basically my fuel tank is buiding up a massive amount of pressure, even on reletavly short trips.
When I remove the filler cap after every trip (which I have to do now) it is almost blown clean out of my hand as the pressure build up is that bad.
I have blown out all breather pipes, changed the filler cap three times, changed the fuel filter and also changed the gravity valve which fits in one of the breather pipes.
I even drilled a hole in the top of one of my spare filler caps, obviously this stopped the build up of pressure but the fumes were making their way back into the car which isn't that nice after a while, and i like the smell of petrol.
Apart from this the car runs spot on. :dontknow:  
Any feed back regarding this would be greatly received.
Many thanks, allsorts.

Apart from this the car runs spot on.   

By its design you are supposed to have pressure and hear a hiss when the cap is removed . Slight pressure helps running .

What is happening when it pressurises ? Does it cause all the fuel to gush out ? Stall the car ?

The pressure build up is so great its forcing fuel to leak from the filler pipe at the last jubilee clip before it enters the tank.
I know there is supposed to be some pressure, but I've owned nothing but VW's for the past 15 years and never have I had anything like this, it realy has to be seen and heard to be appriciated.

allsorts

I still think you are looking at a breather problem in the tank area . Have you been under the car and checked the breather that hangs near the back of the spare wheel well ? This can get blocked with road much . Also remove the gravity valve and blow down both lines that connect to it .

I remember this happening to someone a few years ago when this site was the 'Campaign Register' and it turned out to be a bloked pipe from the tank . Also if the gravity valve is not in the upright position all sorts of strange thinks happen .

Thanks Chudd…….

I did blow down both pipes from the gravity valve and both seem to be free of crud.
I realy thought i'd cracked it before putting the gravity valve on as when you blow in the new valve, air flowed freely one way, but I realy had to blow very hard the other way, like blowing up those silly long baloons.
Where as the old one wasn't allowing me to blow through it at all in the direction from the tank. 'BINGO' I thought, but no.
Am going to have another look at it this weekend, if it stays fine!
Thanks for the replies though. I'll keep you posted. :?

looking forward to your reply as mine's doing the same!!

its got me stumped. all breathers and gravity valve replaced, but to no avail.

are there any other pressure regulating valves?

Is the heat shield still on the tank to protect from exhaust heat?

allsorts said

The pressure build up is so great its forcing fuel to leak from the filler pipe at the last jubilee clip before it enters the tank.

I have exactly the same problem on my Campaign, fuel is getting past the jubilee clip and dripping onto the floor.  :x  This problem has only come to my attention in the recent warm weather. Taking the fuel cap off results in quite a rush of air etc.

Would be interested in any comments as to how to help resolve this. Have looked at all the suggestions above but to no avail.

VW-ONE said

I have exactly the same problem on my Campaign, fuel is getting past the jubilee clip and dripping onto the floor.  :x

Result:
Pin hole corrosion on fuel tank (near jubilee clip) to blame. New fuel tank fitted.  :roll:

ive just fitted a patern fuel tank to my GTI (someone had replaced the filler neck and not bothered to flush the tank)i filled it up last night and had the filler cap practicaly  throw itself at me. thought id check the pressure today and got covered in petrol!!

just wondering if this is due to the exeptionaly hot weather or is there a filter in the breather system that could be blocked?

is the car ok to drive for the time being?

Hey boogaloo, just came across this thread - read the post by geezer. Sounds like what you're experiencing. Not quite sure what geezer means by a baffle, aware there should be a flap in this place. Did get to look at the new tank before fitted?

Don't worry, can't be far from ironing your fuelling problems :borg:

the new tank isnt fitted with this flap or baffle.thats probably why its 70 and not 300 quid.

time to source a good 2nd hand VAG one then

still,at least it runs

tanks for the help markone(tanks, geddit!!! sorry)

Crazyquiff migh have a good tank. Might be able to get him take one to Gaydon to pick up?

So does all this mean GSF tanks aren't worth fitting or is there a way round this :dontknow: .

Cheers

markwon said

So does all this mean GSF tanks aren't worth fitting or is there a way round this :dontknow: .

undoing the filler cap very slowly to release the pressure works.just glad the cars running!!

think il get a genuine tank and fit it over the winter