Gas Vapor Leak / Gas Tank Pressure Vent?

[ViPER1313]

My SHO is leaking gas fumes out of what appears to be a vent line coming out of the top of the gas tank and dumping near the fuel filter (it is one of the 2 lines circled below - not the one that goes to the fuel purge canister.) The line was wrapped in a plastic grommet with tape all around it. The gas tank appears to still be pressurized (when I open the gas cap there is a large hiss of gas.)

Is this line supposed to go somewhere (it doesn't appear that it does)? Why is it venting gas fumes? I am not losing any gas mileage, nor is the car leaking any actual gas.

 

[92MTX]

Looks like the vapor return line..
It should hiss, the system is somewhat pressurized.

 

[pjtoledo]

check the restrictor tube in the vapor line under the radiator, there is a small orifice in it that plugs up preventing the venting of vapors and pressure to the canister. there isn't supposed to be a line that "dumps" anything anywhere near the fuel filter. it's all a closed system, the only vent of sorts is thru the canister.

 

[ViPER1313]

What is this 4th line for then? I see 3 going to the front of the car (one is what I assume to be vapor recovery, one is fuel to engine, one is fuel return.)

You can see there are 4 lines in the picture above. Like I said, it appears to be a dump tube of some sort (prevents over pressurization????) . I don't see any hoses that it was / could be connected to.

The gas smell only occurs after I am driving for a while. Last time I noticed it, I opened the gas cap and got a huge "WOOSH" of pressure being released when I did.

Q1 - What exactly is this 4th line.
Q2 - If it is an over-pressurization line, what should I check / clean on the vapor recovery / relief system to fix it?

 

[ViPER1313]

No-one knows what the 4th line coming out of the tank is supposed to do or where it is supposed to go?

 

[ViPER1313]

Revived from the dead, found the issue and figured I would post it just in case anyone else runs into this issue.

The 4th line on top of the fuel tank is an over-pressurization dump tube that only allows vapor to come out if the engine's vapor recovery system is not functioning correctly. When I would open the gas cap after 1hr of driving, there would be a huge WOOSH of gas vapors escaping.

The problem was that the T fitting for the vapor recovery line going from the gas tank to the engine / charcoal canister was clogged, causing the gas tank to over-pressurize because none of the vapors were being burned while the engine was running. This T fitting is located on the lower drivers side of the radiator support underneath of the radiator drain plug. It has a tiny brass restrictor inside of it with a hole the size of a sewing needle that became completely plugged up. I took it off and blasted it with carb cleaner, put it back on and now there are no more gas smells. The engine also seems to run a bit better at part throttle but this could just be my imagination.

If you have never cleaned this fitting its worth the 5 minutes to do so the next time you do an oil change. I also have a strange feeling this was caused by the 10% ethanol blend being introduced - it seems to love clogging things. In the past 2 years I have had 3 carburetors become clogged in similar fashions - none ever had problems for the first 10 years of use.

 

[mattsho1993]

similar problem here, i noticed the smell of gas and have no leaks. I follow my blood hound of a nose, and notice it behind pass. rear tire strong smell..... when i first got the car that hose going from gas tank to T was unplugged it was dry rotted i cut it and put it back on never noticed the smell till today? SO... should i check the "pinhole" in the T???

 

[Racer X]

I clean mine once a year, but never knew why it was getting plugged.

Now I know.

 

[mattsho1993]

checked the T and its not clogged

 

[ViPER1313]

checked the T and its not clogged

Could be a number of things. First, are you sure that the fuel smell is coming from the dump tube by the passenger side wheel well? Try opening the gas cap after driving for a while - is there a huge release of pressure when you open it? Make sure you don't have any cracked fuel or vapor lines, and that your fuel filter isn't all rusted out an leaking.

After I had verified that I was not leaking fuel, the first thing that I checked was the vapor purge solenoid under the coil pack that connects the top of the T to the intake manifold. You can wire it directly to a 12v power source (I hooked 2 small wires to the battery terminals and touched the ends to the connection leads on the solenoid - it should give a nice "click" when it opens.) I also had a vacuum pump hooked up to it - it clearly released the vacuum when opened.

Next I checked the vapor line from the gas tank to the engine. I hooked up the vacuum pump directly to the gas tank vapor line at the T, gave it 20 squeezes or so, then opened the gas cap and got a small hiss of released vacuum - this let me know that the line was clear.

You can also check the port on the intake manifold to make sure it is not plugged. I can't help you if it's an electrical issue with the purge solenoid wiring, not an expert on how that is routed or triggered. If the lines are in good shape, the purged solenoid is worked and nothing is plugged, I don't know how to help you. Maybe a new gas cap?

 

[SHOstuff]

...and you say this "T" is by the radiator?

 

[SHOtimer]

...and you say this "T" is by the radiator?

Dude, this thread is 2 years old!

Yes, the 'T' is under the radiator, it is right by the radiator drain spiget. The vaccuum line from the intake manifold goes into the middle port, then one side goes to the charcoal cannister in front of the drivers side wheel, and the other goes off to the right (IIRC it comes from the gas tank)

Take the hoses off the 'T' and clean the 'T' out. It has reducers in it, so you can use a small pick to clean it out.

Doug