Pressure In Gas Tank

[logic]

When I open my gas cap alot of pressure is released, sometimes spewing out small amounts of gas. When I start the car in the morning, alot of white smoke is comming out of the exhaust. Does anyone know the cause of these problems and how I can fix them. Thanks alot.

[lex90]

Gas tank is under pressure - normal.

White smoke - likely that power steering fluid is leaking via the air control valve causing white smoke.

[dole2000]

I get a lot of pressure in my gas tank when the weather is hot. It really makes a sucking wispy noise. During the winter not and issue. I thought I would have and issue when I smogged the car but nothing was said.

Air control valve is probably the white smoke.

[logic]

I get a lot of pressure in my gas tank when the weather is hot. It really makes a sucking wispy noise. During the winter not and issue. I thought I would have and issue when I smogged the car but nothing was said.

Air control valve is probably the white smoke.

Where is the air control valve and does it have anything to do with the pressure building up in my gas tank. Thanks for your response.

[92Lex]

Replace your fuel filter.

[logic]

Replace your fuel filter.

I will change the air control valve to stop the white smoke, and I have read that the charcoal canister can cause pressure to build up in the gas tank...is this true? Don't want to change it if it's not broke.

Thanks.

[92Lex]

An EVAP canistor that is saturated can cause a slightly rich running condition, but it doesn't seem like it's your problem though.

[74KDD]

Here is my suggestion for your pressure build-up from the gas cap / tank:

http://www.lexls.com/tutorials/maintenance...lcapgasket.html

74kdd

[larryp]

A clogged EVAP canister can cause excessive pressure to build up eventually to the point of bending the gas tank and causing a leak. The gas cap is designed to let air IN when the pressure in the tank is less than outside air pressure but does not allow excess pressure in the tank to escape. Not saying this is your problem but it could be. Do a search on my userid for leaking fuel tank and read the saga i went through... :whistles:

[logic]

An EVAP canistor that is saturated can cause a slightly rich running condition, but it doesn't seem like it's your problem though.

What can cause the EVAP canister to become saturated because I do have a rich condition and where is it located? also cost to replace?

Thanks

[logic]

Gas tank is under pressure - normal.

White smoke - likely that power steering fluid is leaking via the air control valve causing white smoke.

I changed my engine because of a air control valve problem which was causing large amounts of white smoke to come out the exhaust so I thought the engine was bad, cost me $2,000 to change. My old engine had 200k and my new one has 85k, makes me sleep alittle better at night knowing that I have a low milage engine now but I still wonder how far the old engine would have went...these cars were built for space travel...incredible. Wish I had found this website sooner.

[92Lex]

A clogged EVAP canister can cause excessive pressure to build up eventually to the point of bending the gas tank and causing a leak. The gas cap is designed to let air IN when the pressure in the tank is less than outside air pressure but does not allow excess pressure in the tank to escape. Not saying this is your problem but it could be. Do a search on my userid for leaking fuel tank and read the saga i went through...:whistles:

Please....one pound of additional pressure will not bend a gas tank...that's absurd. Do you even know what an EVAP canistor was desgined to do?

[larryp]

Please....one pound of additional pressure will not bend a gas tank...that's absurd. Do you even know what an EVAP canistor was desgined to do?

Sorry to burst your bubble but i've "been there and done that". Did you bother to read the post detailing my "saga"? And as a matter of fact i do what know the the canister is designed for. It is part of a CLOSED loop system and when part of that loop is closed, pressure builds in the remainder of the system. Now clogged and saturated aren't the same thing, but i was simply responding to let the poster of additional symptoms / problems related to the EVAP canister gained from my own personal experience.

Next time, do your homework before you post a smart a$$ comment.

[92Lex]

An EVAP canister is designed to hold the excess hydrocarbon vapors and purge it into the intake during closed loop, cruising speeds. Have you ever tested an EVAP system? You can only introduce 1-2 lbs of air into the test valve before it becomes a dangerous situation. So how much pressure did it take to "bend" your fuel tank?

You know how I know that a clogged EVAP canister will not bend a gas tank? Well, ummm...I've removed the EVAP canister from my current car. The lines for the EVAP canister are plugged/capped off.

Oh yeah, I'm also an ASE certified auto/smog tech.

[logic]

An EVAP canister is designed to hold the excess hydrocarbon vapors and purge it into the intake during closed loop, cruising speeds. Have you ever tested an EVAP system? You can only introduce 1-2 lbs of air into the test valve before it becomes a dangerous situation. So how much pressure did it take to "bend" your fuel tank?

You know how I know that a clogged EVAP canister will not bend a gas tank? Well, ummm...I've removed the EVAP canister from my current car. The lines for the EVAP canister are plugged/capped off.

Oh yeah, I'm also an ASE certified auto/smog tech.

92Lex, what so you think is causing this high pressure to build up in my gas tank after I drive for a while and can it cause my car to burn rich and move off sluggish. I have a 1992 LS400.

Thanks

[larryp]

An EVAP canister is designed to hold the excess hydrocarbon vapors and purge it into the intake during closed loop, cruising speeds. Have you ever tested an EVAP system? You can only introduce 1-2 lbs of air into the test valve before it becomes a dangerous situation. So how much pressure did it take to "bend" your fuel tank?

You know how I know that a clogged EVAP canister will not bend a gas tank? Well, ummm...I've removed the EVAP canister from my current car. The lines for the EVAP canister are plugged/capped off.

Oh yeah, I'm also an ASE certified auto/smog tech.

Thanks for the reply. So tell me this - what would have caused so much pressure to build inside the gas tank that it pushes the wall of the tank outward creating a hairline fracture at one of the bends? Could a bad check valve on the canister allow excess pressure to build in the tank?

[logic]

An EVAP canister is designed to hold the excess hydrocarbon vapors and purge it into the intake during closed loop, cruising speeds. Have you ever tested an EVAP system? You can only introduce 1-2 lbs of air into the test valve before it becomes a dangerous situation. So how much pressure did it take to "bend" your fuel tank?

You know how I know that a clogged EVAP canister will not bend a gas tank? Well, ummm...I've removed the EVAP canister from my current car. The lines for the EVAP canister are plugged/capped off.

Oh yeah, I'm also an ASE certified auto/smog tech.

Thanks for the reply. So tell me this - what would have caused so much pressure to build inside the gas tank that it pushes the wall of the tank outward creating a hairline fracture at one of the bends? Could a bad check valve on the canister allow excess pressure to build in the tank?

Yes, I would like to know the main cause for high amounts of pressure in the gas tank as well.

Thanks

[92Lex]

larryp,

A malfuntioned EVAP purge valve may cause a very slight increase in pressure, if any. But definitely not enough pressure to cause any damage to a fuel tank. The charcoal canister would probably be the first to go.

I'm not sure what happened to the fuel tank in your car because I haven't seen it for myself. My guess would be that your car had a defective fuel tank to begin with and it slowly cracked over the years or your car has too much chassis flex.....maybe even a crooked mechanic.

larryp and logic,

Why do you guys assume that there is too much pressure in your tanks? Is it from unscrewing the fuel cap and hearing a lot of vapor escape? But anyways. Maybe the EVAP canister is over-saturated and is no longer able to "catch" the fuel vapors.

There isn't much reason to be worried about fuel tank vapor pressure because there isn't much pressure anyways. If you are experiencing hurricane like vapor wind and fuel splashes then yeah, be worried. I'd be more concerned with high fuel pressure in the fuel delivery system.

[larryp]

While i can't say for sure it wasn't defective before i noticed it leaking, i doubt that as the cause. i was in fact experiencing "hurricane force winds" when removing the cap. It happened especially during the summer months so i'm sure the Mississippi heat contributed to the fuel vapors expanding in the tank. The tank wall appeared to be pushed out from inside. The indie mechanic i took it to blamed the charcoal canister. He suggested either replacing the canister or leaving the gas cap loose to allow the vapors to escape. After repairing the tank and removing the gas cap air valve i haven't had any problems.

[92Lex]

So you're driving around without a gas cap?

[lacanls400]

I just replaced my fuel tank. I had to much presure in it causing it to leak at the rolled seam. The problem was the charcoal vapor canister. I replaced it also and now the presure is fine. I spent 640.00 on the tank and 280.00 on the canister and put them in my self.

[larryp]

Glad to see you got it permanently fixed. I know it's not real comfortable knowing you've got a gas leak in your vehicle! Now you can rest easy.

[logic]

I just replaced my fuel tank. I had to much presure in it causing it to leak at the rolled seam. The problem was the charcoal vapor canister. I replaced it also and now the presure is fine. I spent 640.00 on the tank and 280.00 on the canister and put them in my self.

Did you smell any fumes or did you just have alot of gas tank pressure, also was you car burning rich?

larryp,

A malfuntioned EVAP purge valve may cause a very slight increase in pressure, if any. But definitely not enough pressure to cause any damage to a fuel tank. The charcoal canister would probably be the first to go.

I'm not sure what happened to the fuel tank in your car because I haven't seen it for myself. My guess would be that your car had a defective fuel tank to begin with and it slowly cracked over the years or your car has too much chassis flex.....maybe even a crooked mechanic.

larryp and logic,

Why do you guys assume that there is too much pressure in your tanks? Is it from unscrewing the fuel cap and hearing a lot of vapor escape? But anyways. Maybe the EVAP canister is over-saturated and is no longer able to "catch" the fuel vapors.

There isn't much reason to be worried about fuel tank vapor pressure because there isn't much pressure anyways. If you are experiencing hurricane like vapor wind and fuel splashes then yeah, be worried. I'd be more concerned with high fuel pressure in the fuel delivery system.

Do you know where the brake switch is located? when I step on the brakes the lights don't come on and I can't shift out of park without the override button.

[92Lex]

LOL!! Really guys? Hhahaha. Good money for the shops!

[larryp]

LOL!! Really guys? Hhahaha. Good money for the shops!

This forum has been a great source of info to help a lot of folks maintain a fine automobile. There is a wealth of experience here that many have gained and shared by working their way through issues to resolution of a problem. Believe it or not, your personal experiences and opinions do not represent the total book of knowledge on this subject ;) . May want to sign up for an ASE refresher course on this topic.