Getting a lot of pressure build up in the gas tank. Car is sitting in my garage with the plenum, runners, and fuel injectors/runners off, and enough pressure builds up to force gas backwards up through the fuel lines. Turn the cap, and get a hiss. What is the issue. Why won't the pressure go to the charcoal canister? I pulled the canister tonite, and it looks pretty non-serviceable. Can't tell if it is just full and no good, or what. I put the cap on to see if it builds pressure tomorrow.

What do I need to do, or should I just put a vented fuel cap on, junk the evap system, and call it even. I hate to vent gas, and waste almost $3 a gallon liquid gold, but I don't feel like spending a dozen hours fixing something......nor hundreds of bucks buying parts......

 

Check out my thread 'Evaporative Emissions Canister', I'm having the same thing. Tons of pressure builds up in the tank. I think the valve right before the canister in the fuel line may be bad. It opens and closes at a certain pressure to let vapor into the canister. So maybe there is always supposed to be a little pressure there? I dont know... I ended up yanking it and venting the line under the car. I have to fit a big K&N Cone in there anyways. At ~1% fuel/day I dont think it'll be a noticable difference to me.

 

I don't think you have a problem. It is normal to hear that "hiss" when you unscrew your gas cap.

When I also had my intake and injectors out, I had pressure build up when the weather got warm and fuel dripped everywhere. I just kept the gas cap off the car and it stopped until I could put the system back together.

 

Mine also did that and it was ok the hotter it is the more presure it will buil, along with the amount of fuel that is in the tank. less fuel = more fume-vapor wich will increase the presure.

later and


GB

rick