High Tank pressure???

[Rock777]

Hello, this is my first post, wanted to let you all know this site is very helpful, thanks. I've searched around for my problem, but can't seem to find an answer. When I unscrew my gas cap, I notice there is alot of pressure pushing out. I have recently put in a 190lph pump, but don't understand how this could cause the problem. I never had this problem with the old pump, but every time I gas up now the pressure is there. Is this going to cause problems? If so, what should I do?

 

[giddyup306]

Is it when you are near empty? IF so this is normal b/c your tank is under a vacuum. IF not then I suggest scanning for an evap code.
Hope it helps

 

[Rock777]

It is usually when it is close to empty. Wouldn't the air be sucking in then instead of blowing out since it needs air to replace the gas the was once in there?

 

[giddyup306]

The air is rushing in the tank. Vacuum is pressure which is below atmospheric pressure. High pressure rushes into low pressure therefore creating the noise your hearing. It's normal.

 

[Rock777]

That would make sense if the air was rushing in, but that is not what I think is happening. It definitely feels like the air is rushing out though, but it is possible that I am wrong. If it felt like the air was going in, I wouldn't be worried as I would have assumed it was due to vacuum pressure. I'll pay special attention next time, maybe put a piece of paper or something in front of the cap and see if it blows out or sucks in. Thanks for the reply.

 

[giddyup306]

Like I said scan for some evap codes. Don't remember if it would illuminate the MIL or not. The only thing I could think of that would cause it to have pressure would be a bad canister.

 

[Ray III]

The air is rushing out because the evaporative emissions system is not functioning properly. You have a vent line to the charcoal canister in the engine bay, which stores gasoline fumes while sitting. Then from there is another line to the engine intake to burn off the fumes at the approriate times. This line is opened by a solenoid. Either the fuel tank vent line has become blocked, or the purge solenoid is not opening.

The fuel cap does have a pressure relief valve so you should never encounter a HUGE blast of fumes if it is working correctly despite a failure of the vapor recovery system.

Also the fuel cap lets air into the tank as fuel is used up, so you should not encounter air rushing INTO the tank unless the cap is defective.

 

[Rock777]

That makes sense, thanks. How could I test it? I just changed my fuel pump recently, I wonder if I could have reattached the hoses wrong or something? Hmmmm???? Any input is greatly appreciated, however minimal it seems.

 

[Ray III]

how bout this... yank off the hose on your carbon canister (passenger side of engine bay, lower front) that goes to the fuel tank. This would be the one NOT going to the motor. If it continues to blow fumes out the line is blocked. If it's fine after that plug it back in and unplug the other line. If it blows out when you take the cap off something must be wrong with the canister; replace it or just throw it out and put a vent on the line. Otherwise it is the purge solenoid on that line to the engine.

 

[Rock777]

Sounds like a plan, I will try it. Thank you very much!

 

[Rock777]

I think I figured out what the problem is. I must have pinched the vapor line when I installed the fuel pump recently. I haven't tested it yet, but this would make the most sense given the criteria. Thanks guys.