1995 Chevy Lumina 3.1L Sedan w/ ~182K mi
Over the past 6 months, I have noticed fuel odor just about any time I turn off the vehicle, and I am also experiencing progressively higher levels of fuel tank pressure each time I remove the fuel cap. The fuel tank pressure seems to be greater the lower the level of fuel in the tank whenever I remove the cap. 6 months ago (~Sept) it was only a slight "hissing" periodically when removing the cap to fuel up, but now it occurs at every fill up and seems to have enough pressure to push the cap entirely off had I not been careful to slowly loosen the cap to relieve the pressure.
The entire fuel pump and sending unit assembly in addition to the tank and filter were all replaced about 4 years ago in May 2010 or about 28K mi ago. The issue has just come up progressively over the last 6 months.
Today, I inspected the evap. emission components and lines from the tank to the canister to the purge solenoid mounted on the rear of the engine. All lines are connected and seem to be in operable condition. The line from the canister to the purge valve mounted on the engine is completely free with no obstructions. I blew out the line with compressed air and absolutely no exiting particulates were observed. The lines on the bottom of the canister did not show any signs of wet fuel and there were no carbon particles present in the lines from what I could tell from disconnecting and inspecting. The vapor line from the tank to the carbon canister is not kinked or pinched in any manner.
I believe there is a fuel vapor check valve that resides inside the tank connected to the fuel pump assembly/sending unit. This was all replaced as a single unit as mentioned above. I am thinking this check valve may not be functioning properly and not allowing the vapor to escape into the carbon canister. I tried to apply slight pressure and vacuum on the vapor line connected to the check valve on the tank but no air was able to move in or out even with the gas cap off. However, I do have a full tank of gas right now, so I imagine the check valve will be closed.
The check engine light is not on but since this is an OBDI vehicle I am not sure there are any evap. emission codes anyway.
How can I test the gas tank vapor check valve?
How can I test the vapor purge solenoid located on the rear of the engine?
Please let me know your thoughts as to what malfunctioning component could be causing the excessive fuel tank pressure.
Thanks,