gas cap not holding pressure?

[yellowstang1994]

Hi guys, I've always noticed that when I go to pump gas and release my cap I never hear a hissing sound from the pressure. I don't know if it's a make or model thing or something but from what I've noticed every other car I ever seen does it. I don't think it's the neck because when I had it inspected in august it passed the pressure test and it was doing this before then. Do all your cars do it? Should I get a new cap? And finally what negative effects can a gas cap that doesn't hold pressure cause?

Thanks guys

 

[gcomfx.com]

Gas caps are cheap, buy a new one. Really though, is it cold where you are? Makes a difference on how much pressure can build up. I've heard the engine can have a harder time keeping it primed up. So hot starts are tougher.

 

[yellowstang1994]

It's pretty cold right now, but it's done it ever since I had the car (almost 3 yrs now) I just never really occured to me, i know thats horrible, haha. I don't have any problems with cold starts or hot starts at all. I'll get a new gas cap and see what happens though. Thanks!

 

[gcomfx.com]

I guess if it makes it worse you can always put the old cap back on the car.

 

[drakesdad]

I had to replace the cap on the GTP because it wouldn't seal and CEL came on.....

 

[urban96]

also might wanna check the rubber seal/groument where the filler neck goes into the tank. make sure thats not rotted

 

[trav_19]

i have had 8 vehicles and not one of them ever hissed.....unless my tank was low as hell like fumes.

 

[tjh566]

mine doesnt hiss ???

 

[yellowstang1994]

so maybe it's normal for mustangs not to hiss? can anyone else chime in and let us know if your 94-95 mustang hisses when you take the cap off?

 

[DocZG]

My 94 has never hissed, and i live in TX.... However my bros 90 does, but it doesnt have a stock gas cap....

 

[HISSIN50]

IMHO it should not hiss unless there's a slight restriction in the EVAP plumbing.

As a general rule, a car is more likely to hiss when the tank is near empty and it's hot outside (as was stated).

 

[urban96]

a little OT

does this happen to anyone else..

when your pumping the pump keeps stoping (when it thinks the tank is full from pressure) every 2 seconds

 

[go-stang5.0]

Yea not hissing is generally a good thing. When they test your gas cap, they test its sealing ability so if it passes your fine. Hissing is generally abnormal and is related to the EVAP stuff (bad/clogged charcoal canister, plugged line, etc.). If you dont smell gas around the car (especially noticable if you have the car in a garage) your not leaking vapors from anywhere and everything is dandy. I just think its funny you ask...because most people ask the exact opposite question.

 

[HISSIN50]

a little OT

does this happen to anyone else..

when your pumping the pump keeps stoping (when it thinks the tank is full from pressure) every 2 seconds

I haven't had this on a stang but have on a newer car. I never fixed it but believe it was a bad anti-roll valve. I had to pump gas really really slowly to keep the pump from kicking off. Real PITA.

There should not be pressure inside the tank (as a system) while pumping because the nozzle doesnt fit airtight around the filler orifice.

 

[zZsKyZz]

Unless it's a Cobra it shouldn't hiss.

 

[1TallMF]

Out of all the cars I have driven or even rented over the years, I don't ever recall having any of them hiss when removing the gas cap. My roomate's '07 VW doesn't hiss either, nor do my parents cars or anyone else I can think of. I think it depends on the design of the fuel system. Our EVAP system is designed to vent these fumes so there shouldn't be a buildup of pressure, so hissing, in my mind, would be a bad thing.

 

[gcomfx.com]

Mine has hissed since the day I got it (perhaps it's pissed I put cheap gas in it alot) .... my girlfriend's Grand Am does too. I haven't noticed it on the new Focus, but I'll look for it next time I fill up.

On a side note, I HAVE had EVAP problems. I've thrown most of that junk out because it was filling my engine bay with raw fumes.

 

[HISSIN50]

so hissin, in my mind, would be a bad thing.

Stephane, thanks a lot mang.

 

[gcomfx.com]

Stephane, thanks a lot mang.

 

[trav_19]

if your getting hissing your probley running your tank till its really low... i try to never let it get below a 1/4 tank....and a lot of the chevys advise you to keep the tank about 1/4 also because the fuel cools the fuel pump and in a gm the sender units and pump are all one assembly and run about 700 bucks... so i have been in the habit to keep them filled...with no hissing issues.

about the tank constantly clicking off i have had that issue too just cant remember what vehicle it was with...i had to pump gas into it on the first click it seemed like the vehicle was never gonna finish filling up lol