p38 v8 fuel tank breather?

everytime i fill up with petrol (very often)when i remove the cap there is a hissing noise ,is this normal?.dont know if its pressure or vacum.anyone else get this?where would the breather be located,on the actual cap?the hissing lasts for 2-3 seconds,it runs fine doesnt seem to be starving of fuel.thanks

dove said:

everytime i fill up with petrol (very often)when i remove the cap there is a hissing noise ,is this normal?.dont know if its pressure or vacum.anyone else get this?where would the breather be located,on the actual cap?the hissing lasts for 2-3 seconds,it runs fine doesnt seem to be starving of fuel.thanks

Click to expand...

Don't know if it's normal to be honest. Don't have a V8. Maybe it is as there is a tank pressure sensor involved. The V8 does have a very complex evaporation control system. Read about it in RAVE, if you can understand it your a better man than i am Gungadin.

My 4.6 V8 does the same.

So does mine......

mine to its just normal..

I think its happened on every fuel injected car I have had inc my current one. The lower the fuel level the more the hiss, probably because there is more space for fuel to be vapour (ie expanded) then when nearly full. Well it makes sense to me!

thanks guys,sounds like it is a normal thing for them do will read rave and see what it says.

Perfectly normal; the lower the fuel level, the longer the hiss. As fuel level lowers with use the "space" (vacuum) is filled with petrol vapour, the hiss is vapour escaping.

Mine does the same too

mine tells you about the hissing on the fuel cap?

Hi Everybody
I was going to ask the same question, but i think you have all provided the answer, i have the same on my 4.6 hse,

Brian

The wife's '99 4.6 hisses like a cat but my '97 doesn't make a sound. If the hissing is normal what's wrong with mine?

Mine hisses?? '98 HSE

Mine hisses especially after a long run but I thought it was sucking in to prevent vapour escaping and thereby saving the environment

It's escaping pressure and perfectly normal.

The EVAP thing allows pressure to rise in the tank (with fluctuating ambient temperatures) to 5 - 7 kpa, and then if it rises above that a valve opens and any petrol vapour is sent down a tube to the charcoal cannister (thing by the EAS) where it is sent into the engine next time it's started.

Once you screw the filler cap down, it's a closed system so there could always be up to 7 kpa waiting to escape when you open the filler next time.

It happens with my 2.5TD as well.

RAVE SAYS.


Fuel filler cap
The fuel filler cap is designed to allow the fuel
tank to vent during the first half turn. When
removing, carefully loosen the cap one half
turn until resistance is felt, then pause to
enable fuel tank pressure to be released. Once
the pressure is released (hissing has
stopped), it is safe to fully remove the cap.
When replacing, tighten the cap clockwise
until you hear the fuel cap ratchet at least
three times.

Cheers
Thought it was a blocked breather and the pump was trying to suck the fuel tank inside out. I've seen it happen on GTE Astra

wammers said:

RAVE SAYS.


Fuel filler cap
The fuel filler cap is designed to allow the fuel
tank to vent during the first half turn. When
removing, carefully loosen the cap one half
turn until resistance is felt, then pause to
enable fuel tank pressure to be released. Once
the pressure is released (hissing has
stopped), it is safe to fully remove the cap.
When replacing, tighten the cap clockwise
until you hear the fuel cap ratchet at least
three times.

Click to expand...

wammers said:

RAVE SAYS.


Fuel filler cap
The fuel filler cap is designed to allow the fuel
tank to vent during the first half turn. When
removing, carefully loosen the cap one half
turn until resistance is felt, then pause to
enable fuel tank pressure to be released. Once
the pressure is released (hissing has
stopped), it is safe to fully remove the cap.
When replacing, tighten the cap clockwise
until you hear the fuel cap ratchet at least
three times.

Click to expand...

Does this mean the tank is designed to withstand pressure and vaccum?
I would have thought there would be a vent/release or intake system so when the fuel level goes down it lets air in and should it become pressurised by fuel vapour (hot day) it would release it.
any comments by anyone?
Regards