Gas tank has pressure in it. Whats stopping it from venting?

[BlackFox5.0]

Whenever i open the gas cap pressure is relieved. I don't think that the tank has come down before so don't know if the vent line has been pinched or not. I thought maybe the casiter solenoid wasn't working, but then I remembered that cansiter doesn't hold pressure, only fumes, which are purged by the solenoid. What other things should I look for?

 

[HISSIN50]

i thought the vent went up to the charcoal cannister..??

i dont have a Yount-like understanding of it, but a few cars of mine either let out a bunch of air or suck some in (i just hear it) when i remove the cap. always figured it was somewhat normal.

dont some gas caps have a vent of some sort too?

well as you can see Chris, im not sure. im just tossing out stuff for others to kick around.
good luck.

 

[BlackFox5.0]

The whole idea of the canister is to prevent gasoline fumes from entering the atmospere. Having a vented cap would defeat it's purpose. Oh yeah, when I pulled off the hard plastic line coming from the tank and took a wiff of it, I smelled like raw fuel. So I don't know, maybe my canister is bad?

If your tank hisses when you open the cap, something is wrong. My GT never did this.

 

[Michael Yount]

The vented cap will let air enter, and if the pressure reaches too high a point, it will act like a relief valve and release an over pressure. But it shouldn't be venting a noticeable amount when you pull the cap off. So either the vent line is pinched/plugged somewhere, or the purge/cannister system is malfunctioning. Have you pulled the codes to see if you're getting a purge valve error code? Temporarily pull the tank vent line off the canister. Drive around a bit - if you pull the cap and the pressure's relieved, the problem's likely in the purge circuit/system. If that doesn't relieve the problem, the vent line is not clear between the tank and the cannister.

 

[HISSIN50]

The vented cap will let air enter, and if the pressure reaches too high a point, it will act like a relief valve and release an over pressure. But it shouldn't be venting a noticeable amount when you pull the cap off. So either the vent line is pinched/plugged somewhere, or the purge/cannister system is malfunctioning. Have you pulled the codes to see if you're getting a purge valve error code? Temporarily pull the tank vent line off the canister. Drive around a bit - if you pull the cap and the pressure's relieved, the problem's likely in the purge circuit/system. If that doesn't relieve the problem, the vent line is not clear between the tank and the cannister.

and the man has spoken. thanks for the education.

 

[shorty1993]

i removed the whole system, canister, purge valve, line to intake and all. then pulled the back close to tank and cut it off. i will get the rest when a new fuel pump goes in. i have had no codes or side effects from doing this. it cleans up the engine bay as well. micheal may have some reason why this bad, but i have had good luck so far.

 

[Michael Yount]

shorty - just be sure to keep the tank well vented. For fuel to come out, air must be able to enter or you vacuum lock the fuel pump. And remember, it's a return-type fuel system. The pump runs at max - what the engine doesn't use gets recirculated back into the tank. Especially with the big pump that's going in, that keeps a lot of fuel coming and going from the tank which creates a fair amount of vapor pressure - think what happens when you shake up a small container of gasoline that's partially full of gas (the rest is air). What a lot of people do is run a vent line up the fill tube and into the fuel filler area. That way any fumes can easily escape to atmosphere without being trapped under the car. And of course if at some point an emission test has to be passed, and they see what's been done, that whole set up won't pass muster.

 

[shorty1993]

shorty - just be sure to keep the tank well vented. For fuel to come out, air must be able to enter or you vacuum lock the fuel pump. And remember, it's a return-type fuel system. The pump runs at max - what the engine doesn't use gets recirculated back into the tank. Especially with the big pump that's going in, that keeps a lot of fuel coming and going from the tank which creates a fair amount of vapor pressure - think what happens when you shake up a small container of gasoline that's partially full of gas (the rest is air). What a lot of people do is run a vent line up the fill tube and into the fuel filler area. That way any fumes can easily escape to atmosphere without being trapped under the car. And of course if at some point an emission test has to be passed, and they see what's been done, that whole set up won't pass muster.

it has been set up this for about 6 months without a problem, i will keep an eye on it. right now i left it vented near the pass rear wheel house. however when the tank comes down i plan to do a little more plumbing to complete the job. i just didnt want to give him the wrong advice. i tend to try things sometimes without knowing the the direct outcome, but that how we learn. thanks Micheal.

 

[Michael Yount]

About the only complaint I've heard on removing the cannister/purge system is that for folks with closed garages, they sometimes complain about the odor of gasoline when the car's been sitting for a bit.

 

[shorty1993]

at i had it cut under the hood and had a smell when driving, but seems fine now. always to hear from you thou.