pressure from fuel tank ?

[versa071979]

hello everyone I am new here on the pathfinder forum My check engine light came on the other day and I have not pulled any codes yet because i just ordered a new scanner should have it anyday now my question is when I remove my gas cap alot of air pressure is being relieved is this a sign of any specific problem ? this is a 2001 3.5 le path 4x4 with 90k

[C-Kwik]

No, pressure in the tank is normal. Its how the system tells if there is a vapor leak.

[versa071979]

a vapor leak meaning a vacume leak somewere any one have any other info on this ?

[ARKQX33V6]

Canister in the rear is monitored via the gasoline vapors, that are contained vs. the escape via the gas gap and the complete fuel system that works as a whole and this includes the fuel filter, the fuel rail and the intake system to the throttle. As the tank lowers in liquid fuel a greater volume of space is available to the vapor build up and if the system is working that volume vs. pressure is regulated. If for any reason that pressure is too great or there is too much vapor loss a trigger is set and you get a spill over alarm code. You must read that code and like all codes they are relative to the problem although they may not indicate each exact problem. But knowing the code will lead you to the problem as you test for example the gas gap valve or the fuel line clips that made a hole in the fuel line.