Pressure in gas tank

[smartaxel]

Hi folks,

I seem to have pressure in my fuel tank. I went to refill the gas tank today, and when I opened the gas cap, it seemed to release a good amount of pressure. I've got a 92 VR-4, with a 93 engine, and running Chrome 2.0. I am running all the factory vacuum lines and EGR/Purge. For the purge solenoid, I swapped in a solenoid from a 96 non-turbo 3000GT. I'm assuming there should be no pressure in the tank, and it should be let go by the purge solenoid. Later model VR4s also had a one-way valve and different purge setup to that charcoal cannister. Does anyone have experience with this? Perhaps, I need to change something related to when the purge solenoid purges? Or, perhaps install a one-way valve on the charcoal cannister? (Maybe boost is getting into the tank?). This is above my knowledge level, and I'm just randomly guessing.

Does anyone have any thoughts?

Thanks!

[stealthify]

I don't think it's a cause for concern, all of my cars have done this to a degree. More so when I run the tank closer to empty, and especially on warm days.

[sergechronos]

As with Stealthify; I've seen it on every car I've owned, only constant has been that I've been fairly low on gas and it's been hot out. I would assume it's just fuel vapors having the right condition to expand in the tank and then rush out when you open the gas cap. So long as there are no changes to your ability to start up or anything, I wouldn't worry about it.

[Roybatty]

Had similar issues in a g20 van. I never resolved it. Hot days were worst. It would also affect fuel deliver :eek: quick solution was to not close gas cap tight.

I suspected gas cap and/or malfunctioning vapor canister.

Revel in your time

[green-lantern]

+1 on not worrying about it. Almost every car I’ve owned does that.

[Greg E]

Both my 98 and 99 VR4s did this during hot days.

...and that with functioning factory flash ecu purge equipment....

[IPD]

it's a feature

/steve jobs

[fastfalcon94]

Mine does it too but I got rid of my charcoal canister. I swear when i did the delete though that one of the lines is supposed to vent in the back. I know people who did it said if they parked it in a garage for a wihle it would smell like fuel. Maybe I didn't do something right. I've been meaning to look into it but haven't yet. It's definitely at it's worst when it's hot out and I'm low on fuel.

[smartaxel]

Thanks guys. This is the only car I have had do this. Wierd that it's "normal", but so be it! Thanks again

[KeithMac]

I removed all the purge crap and ran a line to the air filter/ or just drop a line down near the floor. There is also a valve on top of the fuel tank (blue?) that restricts purge action, if it sticks shut you could end up with fuel starvation issues.

[DrGonzo]

The tank is supposed to do that. When the system is stock it pressurizes the tank as the fuel evaporates. That EVAP system only allows pressure out when the system is running as it is solenoid controlled. Solenoid only opens at a certain PSI to relieve the pressure. When it sits overnight, the tank is low and it gets hot. It has more room for the fuel to evaporate and expand. I believe the pressure control helps to stop fuel from evaporating right out of the tank.

When the Evap system is removed the tank should no longer pressurize as you are venting it to atmosphere and there is nothing to hold in the pressure unless you have crimped your vent line in which you would have other problems like not being able to fill your tank without it spraying back at you.....LOL Ask me how I know!!!