hi

 

I´m still trying to sort out the problem I’m having with the petrol tank.

 

I know all about the petrol tank causing a slight vacuum through pumping the fuel and the air not being replaced entirely until the vacuum pressure opens the valve on the petrol cap to allow air in but mine is doing the opposite, when I open the fuel cap air isn´t being sucked in it’s actually being blown out, so much so that if I jam the small valve on the petrol cap open it starts to spit petrol out. How can the petrol tank be under pressure like that? :confused: I have to open the petrol cap every 20-30 km to release the pressure otherwise the pump starts to fail.

 

Any ideas would be greatly appreciated.

 

Maz

Ossian

 

No worries on the fuel cap saga mate .and cheers for the info now, makes me feel confident that I will be tackling the right thing when I set to work on the car tomorrow :)

 

Stu

 

the rush of air being pulled into the tank when you open the cap is normal mate that´s the so called negative pressure caused by the pump pumping the fuel out..we´re on about positive pressure in the tank..so no worries for you there. but cheers for the input.

 

:)

Ossian

 

No worries on the fuel cap saga mate .and cheers for the info now, makes me feel confident that I will be tackling the right thing when I set to work on the car tomorrow :)

 

Stu

 

the rush of air being pulled into the tank when you open the cap is normal mate that´s the so called negative pressure caused by the pump pumping the fuel out..we´re on about positive pressure in the tank..so no worries for you there. but cheers for the input.

 

:)

hi maz just wondered if you found solution to your excessive fuel tank pressure as i have the exact same symptoms

Unfortunately he hasn't been active since May, but you can hope :)

 

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Oh and welcome mate

Unfortunately he hasn't been active since May, but you can hope :)

 

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Oh and welcome mate

Just new on site and not very computer literate ,sorry

I'm sure if you start a thread in the Help section some of the people here could try to help you out.

having removed my fuel tank and stripped it and refitted it, there is 2 way check valve not sure if it the the same line thats goes to the carbon canister if you blow on it hard the air can leave the tank and if you suck on it the air can come into the tank now its harder to blow ie air out the tank than it is to suck air ito the tank if you have one to hand you will see what i mean. if that valve was not working or even a block not sure on the line thats runs from the the tank to the carbon canister then you would indeed get a masive vac in the tank as the fuel level goes down . if you were to remove the check valve and carbon canister the van in the tank would be gone. not that this is a good idea. i have removed the carbon canister. but if you got rid of carbon canister can get check valve that flow more easy ie with less pressure your issue would be gone

 

there is 2 pipes that connect to the top of the tank i think the thin pipe in the pic if mine here is the one with the check valve on it

Edited November 10, 201510 yr by dan300zx

Thanks dan300zx

i have removed carbon cannister but still getting excessive pressure when opening cap on tank

Thanks dan300zx

i have removed carbon cannister but still getting excessive pressure when opening cap on tank

 

Do i need to remove tank to get at check valve please.

you mite be able to get to it with tank in place i had tank of at the time the valve it bolted to the chassis if i remember am looking in my pic to see if i can find it if that not working you can just but another 2 way valve and the problem will be sorted i bet money on it as it let air in and out of the tank so its it fooked the tank can breath in and out as the fuel level changes

this is not my my car its just a pic of a 300 i just found but there it is so yes just jack the car up you can remove it and see the vac issues goes but dont leave it off get a new one if its fooked, there could be a block in the pipe that goes into the tank and the valve is ok so unplug and suck on the pipe and blow to make sure its clear only a bit mind as the fuel vapor is very bad for you lol

its also a bit odd that you have got rid of the carbon canister and its still doing it as that would vent the tank to so maybe that line is blocked ?

Thanks very much i will give it a try ,any idea where i could buy another one

before you do that get the end of the pipe were you deleted the carbon canister and suck on blow on that it should be free to blow and suck if you get me

Are you sure it is pressure being released and not vacuum?

Yes its definitely pressure help please.

Are you sure it is pressure being released and not vacuum?

 

Yes its definitely pressure i can open and close cap continuesly and pressure comes out help.

the tank cant be breathing then can it if it was you wouldnt get vacuum or pressure

Edited November 11, 201510 yr by dan300zx

the tank cant be breathing then can it if it was you wouldnt get vacuum or pressure

 

Thats right sucked and blew through pipe as you suggested it seems to be clear

if there is a hole in the tank via the old pipe that went to the carbon canister in effect a hole in the tank how can pressure or vacuum build it make no sense thats like trying to pump a car tyre up with a hole in it

if there is a hole in the tank via the old pipe that went to the carbon canister in effect a hole in the tank how can pressure or vacuum build it make no sense thats like trying to pump a car tyre up with a hole in it

 

Yes exactly, do you think it might be a fault in the check valve when under pressure or vacuum

if there is a hole in the tank via the old pipe that went to the carbon canister in effect a hole in the tank how can pressure or vacuum build it make no sense thats like trying to pump a car tyre up with a hole in it

 

Yes exactly, do you think it might be a fault in the check valve when under pressure or vacuum

i cant remember 100% if the line with the check valve is the same one that runs to the carbon canister. just unplug it from the valve so the tank is venting to the air, as a test but dont leave it like that of coarse its just a test

Discovered check valve to be faulty it lies between tank and carbon cannister does anybody know where i can purchase one its a 1992 swb fairlady japanese import thanks

cool man had a idea it would be that you can buy a better after market one

Any idea who from