hi all I've got a 2005 focus st-3 engine management light on 2 fault codes p0087 and p2178 in limp mode only boosting to quater on boost gauge, now a strange whoosing noise comes out the petrol tank when I remove the petrol cap like a blowing or sucking noise, any advice or suggesting please. Thanks in advance.

yeah its meant to its a pressurised system and the cap isnt vented

P0087 is fuel rail pressure is too low

P2178 is system too rich off idle

ive heard that the fuel sender fuel filter gets clogged and can cause this as ive said before the system needs tested for pressure the fuel pump needs tested this can be done by ford on the computer so they can see the live data and see where the issue is

hi fella

when you drive and use up your fuel it has to be replaced with air or the tank vacuums and can cause fuel starvation.

there should be a vent or valve to let in the air, it will be blocked up .

if its built into the cap it will need replacing. short term fix loosen cap a little .

hope this helps

take no notice of the person who said the tank is pressurised its rubbish, it will have a certain amount of vacuum before it opens the valve to let in the air . this is so because the fuel cannot leak out if the car was on its side. if the air was not replace the symptoms are fuel starvation, lack of power on longer journeys, it will stop and draw no more fuel and the tank could implode.

rubbish really all fuel systems use pressure the tank has pressure in it as you said from the fuel going down and air filling the void so when he removes the cap which isnt vented on the focus the air is released yet to find any focus that doesnt do that theres a goggle valve in the system that prevents fuel from spilling out when the cars overturned

I am a mechanic of 30 + years. I have city and guilds levels 1 2 3 and specialised in vehicle electronics . I hold other institute certificates, if you want a lesson in fuel systems that is not a problem. a fuel tank is not pressurised you cannot compress liquids and ive never seen a compressor connected to a fuel tank . please don't comment on what you do not understand.

a fuel tank isnt pressurised, but the cap isnt necessarily vented either, especially on sealed systems.

the venting is done through the evaporative emmission canister.

hissing isnt unusual...especially on a tank low on fuel...sometimes it does it, sometimes it doesnt...some cars it happens every time.

with those codes showing your problem definitely sounds fuel pressure related

thanks For all replys, I've hade it on a proper Ford diagnostics but don't rink the bloke new what he was doing, can any1 recommend a good garage in the west midlands where I can take it to check the fuel pump and fuel pressure ??? Thanks

a fuel tank isnt pressurised, but the cap isnt necessarily vented either, especially on sealed systems.

the venting is done through the evaporative emmission canister.

hissing isnt unusual...especially on a tank low on fuel...sometimes it does it, sometimes it doesnt...some cars it happens every time.

with those codes showing your problem definitely sounds fuel pressure related[/quote

Hi m8 thanks for reply, yes its defo fuel pressure, any idea what 2 change or check first ? Thanks

what is causing this ? Fuel pump ? Fuel rail ? Injections ? Sensor ?

could be a number of things to be honest

fuel pump

blockage

fuel pressure regulator

fuel injector

in theory, could even be that evap cannister purge valve

by the way...to dot the i's etc....hiss isnt air escaping, its air entering...so there is a certain amount of vaacuum going on, but that isnt unusual, unless the purge valve/ system isnt working in which case, when they completely fail, car would gradually lose more and more power and tank can indeed collapse in itself untill you release the cap

pre emmission tuned cars [ie old skool] hissing was as Simon states, classic symptom of blocked tank vent/cap