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Fuel Cap Doesn't Go Pssh

SargeRX8

By SargeRX8,
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SargeRX8 Grand Master

SargeRX8

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I hate it when my car makes PSSH noises, but the one I have noticed is not evident, which probably should be, is the fuel cap. No matter how much, or how little, fuel is in the tank it just doesn't go pssh when I open it. All our other cars do. I have been getting a strong smell of fuel in the cabin and someone said it could be the fuel cap. What are the causes to this?

Ive swapped another fuel cap in there from my old skyline which I am 110% certain went pssh when I opened it but haven't driven the car yet to build up pressure in the tank.

Could there be another issue? I'm not having any issues with the car, just this smell on start up and the only noticed this when the dude told me to try it out. Injectors are not/should not be leaking as I am not running rich enough to cause starting or firing issues anymore, and they are using all brand new seals all round.

Its an R33 GTS25T lol. Is it normal for it to go pssh or does it not matter if it does or doesn't.

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https://www.sau.com.au/forums/topic/372701-fuel-cap-doesnt-go-pssh/
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mad082 Grand Master

mad082

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pretty sure mine did, but it was so long ago now. my current car doesn't and i've been thinking about getting a new cap to see if it makes it hold pressure a bit more as it may also improve my fuel economy a tiny bit.

in your case it may be the cap that is the issue (or more to the point, the little rubber o-ring on it) or possibly the rubber seal around the top of the fuel tank where the fuel pump is accessed.

DVS JEZ Grand Master

DVS JEZ

Posted
Posted

It may possibly be the fuel cap insert fitted during compliance. It is fairly common for this to leak.

Its the part that the fuel cap screws into. It needs to be pryed out, cleaned and resealed with gasket goo. Refit and try not to move it for 24hours or so to let the goo set properly

SargeRX8 Grand Master

SargeRX8

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Thats what I would like to know too. Its clearly holding pressure so one would assume it would have an effect on the overall fuel system if there is no pressure in the system. Tomorrow ill be fixing mine by gooing up the hose as JEZ suggested.

I know that when my car is parked, I can see the air hazy around the fuel cap area, when the lid is on. So there is definitely something going on there.

Edited by SargeRX8
mad082 Grand Master

mad082

Posted
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only way that a fuel cap can affect fuel pressure is if it is creating a vaccum as the fuel level drops. if this is happening then you would get the "psssht" when you open the cap as it would have to seal tightly. other than that, all fuel pressure is controlled by both the fuel pump and the fuel pressure regulator. if the fuel pump is dying then it won't be able to supply enough fuel and pressure will drop. if the fuel pressure reg is shot then it will simply make the fuel pressure be wrong.

fastjetjockey Collaborator

fastjetjockey

Posted
Posted

only way that a fuel cap can affect fuel pressure is if it is creating a vaccum as the fuel level drops. if this is happening then you would get the "psssht" when you open the cap as it would have to seal tightly.

In addition to this, if you equalise the pressure in your fuel tank during the warmth of the day, then the air in your tank cools at night you will create a vacuum. In fact I'd say thermal expansion and contraction would play a bigger part in your psssht factor than a dropping fuel gauge.

There's only supposed to be two ends in your fuel system; Out of the filler, and to the motor. So If you haven't got any fuel leaks I think we can rule out the submerged/pressurised side. Leaving the filler. I agree with what has been said about your filler cap seals, or possibly a leak in the tube running to your tank. But again, if it's not leaking when you fill up, it can only leave the seals. Try a friends functioning filler cap.

SargeRX8 Grand Master

SargeRX8

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I am aware that is is the pressure of expansion of the fuel in the tank which causes the psssh but it must be going pssh for a reason and Nissan must have designed it as a sealed system for a reason. I just like it when things operate the way they should. Maybe it won't do shit to the car but I don't know, its just the little voice in my head that somewhat seeks normalisation/perfection. If I hear a single squeak or rattle in the car, I'm under it for days trying to check out the cause. Thats just me lol.

The vapor canister is all hooked up. Its a replaced unit(unsure why it was replaced, possible due to damage when the car was majorly guttered). What should I be looking at? They are cheaper than chips to buy and if this could be causing my lack of psssh ill replace it.

mad082 Grand Master

mad082

Posted
Posted

having it fully sealed has 2 benefits. 1 is a side effect of the other. the main reason being that there is no fuel vapours leaking around the car (so if someone walks past with a cigarette in their hand it won't go boom). the side effect of this is that when it is sealed there is a limit to how much fuel can turn from liquid to gas, thus helping with fuel economy.

SargeRX8 Grand Master

SargeRX8

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Today I started the car while the car was facing a southern direction so the sun was behind me. Immediately as soon as the car started I saw the fuel haze coming from the petrol filler cover and the smell hit the cabin straight away. It is definably something going on in there. I doubt it is the cap as I am using two caps, one definitely working from my old car and both rubbers are still fine etc.

I'm gonna try to what jez said, clean the shit out and reseal it. It really did not look safe because if there was any spark or flame in that area the car will go boom.

SargeRX8 Grand Master

SargeRX8

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It was pretty easy. Open the fuel cap and determine if you need to seal it. The metal thing which you put the fuel filler into, and the thing you screw the cap into, comes out. Mine came out WITH EASE. There was literally nothing holding it in place. I pulled it out and cleaned it up with a wire brush and screw driver(when you get it out you will see gunk and shit around the inner lip which holds to the tube you pulled it from). Get some gasket goo stuff which is suitable for use on parts which handle petrol. When you pull the metal thing out of the car and flip it up side down, there is like a U ridge. Fill the U ridge with your gasket goo stuff(I used permatex form a gasket). Apply some to the black tube in the car. Be careful not to drop shit into your fuel tank. Let it set til its tacky then insert it back in, push it down and put your fuel cap back on and let it dry. I drove the car about 1hour later. I didn't want to open the fuel cap to see if it worked so I wanted til the next day and the seal was set. Took the lid off PSSSSSSH.

I'm gonna drop a full tank in there today and see if it has any effect on fuel economy at all. Currently do about 240 - 280 a tank but never let the car fuel gauge drop to the E.

Absolutely no more smell of fuel in the cabin!

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