I took my car in to get a smog a while back in which is passed. although it failed the evap test which fails the whole test. my gas tank builds up a lot of pressure and im not sure how to fix that. i put a new gas cap on and it still builds pressure. i brought it in to express tire and they charged me 300 dollars, and it still does the problem. i need to get it smogged now so i can do registration but my money is ruining dry. does anyone here know whats going on?

when they were about to start the evap test, they didn't even do anything cause they put something in the gas tank and it was spitting out gas. so i guess my question is, what exactly is my problem with my car building up pressure and what my car needs to pass evap when i take it in. no check engine light on.

sorry if this is the wrong spot

 

idk my car does this too. my fuel pump is going out though, i figure its related to that.

 

What did they put in the gas tank?

My car builds a lot of pressure mostly just gets the car smelling a lot like gas. I think im gonna be going with a vented gas cap from modern day muscle and see if it helps any.

Im not sure if its a good or bad thing ive heard some people say u need pressure an others say u dont.

Do you have an evap canister on the front of the car?

 

Not sure why but some of these have a pressure valve beside the left frame rail. I've replaced mine and don't have build up. There are different gas caps for these cars as well, vented and non.

 

take the gas cap off, disconnect fuel lines at sending unit, take an air hose and blow the lines back through the tank. Disconnect the fuel lines at the front of the car,fill them with carb cleaner then blow them out with an air hose. This should clean out any crap in your lines. I would also change the fuel filter and pressure valve like white gold stated. hope this helps

 

mine did this as well. I switched over to a vented cap and all is well. My trans am i had a few years ago kept going through fuel pumps and after i went to a vented cap on that car (it had ALOT of pressure build up) it never went through another pump after that.

 

Vented cap. Ethanol bearing fuel evaporates more quickly. Older Evap systems may not be able to keep up with the volume. I believe Chrysler had a specific recall on this for their older Caravans.

 

Can someone explain what the side effect of having too much pressure in the gas tank is?

What all is affected?

 

Side effects: Feeling like your car will friggin explode at any minute, & or whilst filling gas tank up.

 

Hah yeah figured that one, but does it affect fuel delivery?

 

Ethanol evaporates more slowly than gasoline.

When the premise is faulty, conclusions based on it are also faulty.

I don't know what they do to test the evap system where you live, but in Colorado, they take the cap off, hook the cap to a machine, and pressure test it. It has to hold pressure or it fails. Therefore, a vented cap will fail the test.

Pressure on the tank when removing the cap is normal.

 

A quick Google search (or, opening my thermodynamics textbook from college) will show that ethenol has a lower flash point and a lower vaporization point. Quick quote from an interview with an energy consultant...

"In addition to showing that there are 'no environmental benefits' to ethanol, science clearly shows that there are enormous environmental costs. For example, the general use of ethanol significantly increases air pollution. Ethanol evaporates faster than gasoline. So while gasoline reformulated with ethanol may release less carbon monoxide, it releases more volatile organic compounds, hydrocarbons, and nitrogen oxides."

In addition, a quick search of ethanol impacts on evaporative systems quickly returns many hits...

Ethanol is known to be more difficult to purge from carbon canisters (as are heavy hydrocarbons), so could reduce their working capacity.

Lastly, I just know from repairing a Carvan for a friend, that the newer fuel seems to be having an impact. When I went to the Dodge dealership, the guy behind the counter siad this was becomming a common repair. Older systems that are already worn can't handle the increased load. Replace everything with new parts and it seems to work fine.

 

The statements are contradictory. If ethanol evaporated more quickly than gasoline, it would be easier to purge from the vapor recovery canisters.

That sounds more like the huffing of an anti-ethanol advocate than a scientist. Just because you found it on the web doesn't make it true. Other sources have similar problems: guys behind the counter at dealerships are about the least reliable, in my experience - he might be correct that they are replacing evap systems, but be totally clueless about the cause of failure.

 

May be true. However, I had the experience with the Caravan BEFORE I ever went out on the web reading about this. For the OP, please note that in my experience, replacing the old canister with a new one did fix the problem. This was only about a year ago, but it is still holding up fine. The fuel smell in the car is nearly undectable now. However, the pressure in the tank still builds up.

Anyone here only drive their carb car once a week? I do (its my race car). Try taking the fuel bowel off after the car has been sitting a few days and see whats left in there. I am old enough to remember when the bowels would still have fuel in them (pump twice and turn the key!).

 

I tried a vented cap the other day, seemed to accelerate a little smoother, but i then put back my regular stant locking cap and the car felt like i was being pushed back in my seat a little more(torquier). Is their something to that pressure in the tank? or the CCP system/ and ecm??

 

If you switched from TPI to Carb this will happen, it happened on my truck.
Your best bet is to Drill a small hole in the center of your gas cap, it fixed my problem and it was FREE!

 

i know, i did that but like i said it felt faster with the normal gas cap.

 

I heard drilling a hole does not function the same as having an actual vented cap.

So the cap is actually affecting drivability? I might just get me one afterall.

 

Well, i drilled two small holes and it worked, no pressure in the tank. Although, i found my car to "feel" more torquey with the regular gas cap that is not vented.

 

This is taken from another thread on vented caps. From the research ive done drilling a hole will help for those with excessive pressure as a temp solution but it wont function as a vented cap.

 

guys i posted a very nice thread about gas pressure and evap and gas cap and how to fix ...and u still drilling ur gas caps????? !!!!!!!!!! i clearly explained how the system works and what should u du and what u shouldn and there u go nothing...the thread is right there furst page in carborators section....please read it

 

i wanna check it out,can u post the link?

 

It's this one

https://www.thirdgen.org/forums/carb...-pressure.html

 

Hmm.. have you checkd the pressure relief next to the fuel rail lines, (located by fuel tank)? might be messed up there. Also something you can try is a vented fuel cap, not sure if you would want to. it makes you lose some HP but smoother overall.

 

who told u this?

 

post on previous thread about it, idk what its called but some guy was reasearching on this.