General Fuel Tank Vacuum?!?!

[Most Easterly Pandas]

The Selecta origionally came with a standard Fiat Fuel Tank filler neck cap but of the none locking variety, I decided to swap it with the locking on off of the 750L donor we've got as I don't really want people removing the none locking one.

But I have now noticed that when I go to fill up with fuel, when I remove the cap there is a strong vacuum which sucks into the tank just as its removed. Is this normal? As I've never had it on any of our other Panda's from what I can remember.

Many thanks. Jon.

 

[panda-sport]

This is fairly usual if its a fuel injected car

 

[Chas Uno]

My Uno FIRE with a carburetor has always done that. It's called the "Fiat Fart"

 

[oldernowiser]

It shouldn't be a vacuum - it should be under pressure.

 

[Most Easterly Pandas]

This is fairly usual if its a fuel injected car

That would be why it doesnt happen with the other Panda's then, lol, they're all carb compaired to the injection selecta.

I like the phrase 'Fiat Fart'

oldernowiser - just wondering what the difference is? It seems to suck in air, and you can see fuel vapours around the black plastic on the body work.

 

[oldernowiser]

oldernowiser - just wondering what the difference is? It seems to suck in air, and you can see fuel vapours around the black plastic on the body work.

As I understand/remember it:

the fuel system on an injected Panda has excess fuel provided to the injector and what's not used is returned to the fuel tank under (some) pressure in the second fuel line.
The filler is required to be a good seal (so you don't spill fuel if the car falls over - it's checked as part of the MOT), hence the whoosh when you undo it.

I can't remember what happens on a carbed Panda, it's that long since I've played with one...
But in all probability there is no return pipe, so with the fuel being removed from the tank, and the filler being a good fit you will get some vacuum.

If that's the case, my post further up wasn't correct for all Pandas

 

[tashman]

Mine is a 750 with carb and I always hear that rush of air.

 

[Bill Mitch]

Mine is a 750L (carb) with non-locking filler cap, there is no 'Fiat Fart'.
Just to add to the general confusion there is a return line from the fuel pump.

 

[Chas Uno]

Both my carburettored 999cc Unos had return fuel lines and both had the "Fiat Fart"! The 999cc carburettored Uno's fuel system is identical to that of the carburettored Panda.

Oh yes, you'll only get the "Fiat Fart" if the fuel cap seal is working properly

 

[Most Easterly Pandas]

Mine is a 750L (carb) with non-locking filler cap, there is no 'Fiat Fart'.
Just to add to the general confusion there is a return line from the fuel pump.

OMG so confusing, lol. So what the injection Selecta is doing is right then? Cos neither the 1000cl (carb) or 750L (carb) have the fiat fart, so could the filler caps on them be buggared then?

I know, I'll do a little experiment and swap mine with dads 1000cl for a little while, if the caps a baggared then the fiat fart will disapear on my Selecta and start on his 1000cl in therory?