Here's the story guys. There's always been a strong gas smell from near the filler cap on my car. When I was changing the brake lines I noticed the plastic UFO shaped valve back there that is hooked up near the fuel hoses in front of the tank was covered in fuel residue and smelled of gas. I replaced this part, and for a week or so the problem was solved. I even heard a hiss of pressure whenever I opened the gas cap. Soon that hiss faded, and the odor returned. When my new muffler was being welded on this week, the technician informed me that he accidently started a small fire fueled by vapors coming from this valve when he was using the welder. I felt up under the car and there is indeed fuel residue on the new valve. FYI my car is running at 46 psi of fuel pressure, which is a little high, but my AFPR won't go any lower. Would this be the cause of the valve locking open? The muffler tech. suggested I just plug the hole (delete the valve). Would this be a wise decision? Any advice is welcome!

 

Sounds to me like your canister purge system isn't working. The "UFO shaped" valve is the rollover check valve IIRC. It basically allows air to be sucked into the tank to take the place of fuel as it's used, but does not allow fuel/vapors to escape the tank (especially if the car somehow ends up on it's roof.) Your car is probably eating them because it's building up pressure in the gas tank, because the CCP system isn't purging the excess fuel vapors from the tank like it should. This would also explain the "hiss" when you opened the cap after replacing the valve.

You didn't happen to scrap the charcoal canister and plug the hoses going to it at some point, did you?


edit: I wouldn't plug the line. That will just cause the pressure to build up, and probably find another way to escape. At least now you KNOW where the leak is, and it's easy to get to. It would suck if the fuel pump O-ring on top of the tank started leaking next.

 

Good reply. The canister is still in there. Is there anything else the CCP system other than the canister itself?

 

Basically, you just have the canister and the purge valve. The valve sits on top of the canister and has two hoses going to it....the bottom one goes to the tank, and the top one goes to a vacuum source. My '91Z has it going to the passenger side of the throttlebody. The ECM controls the valve, opening it at part throttle to vent the collected vapors.

Try this: unplug the bottom hose (going to the tank) and see if you can blow air back into the tank. There may also be a check valve between the canister and the hard vent tube that you'll have to remove. If the vent tube is clogged, blow it out with compressed air. Otherwise, the charcoal canister must be stopped up.

 

I noticed the same smell from the same area you are describing. I thought it might be the old gas cap that was not vented, so I bought a new vented gas cap. I figured I would start from the easiest thing first, it seemed as though there was a small amount of gas in the filler neck? If you figure out the fix please post it, I'll be keeping an eye on this.

 

I'm not sure what you mean about the filler neck. We are not supposed to have vented caps on our cars, hence the point of the charcoal canister system. I would take a look under your car, and you will see the big UFO valve I'm talking about. If it's covered with a brown fuel smelling residue, that is your culprit.

 

I was just messing around with an extra one of those "ufo" valves I have laying around in my garage yesterday. I noticed when you blow into the valve, you have to blow kinda hard before it pops and releases air. I guess your tank has to reach a certain amount of pressure, then if the valve is working properly, it'll release the pressure at that point. My guess is that our fuel caps are probably non-vented due to having this release valve.