1985 GT 4BBL with lots and lots of fuel pressure IN the fuel tank.

[foot2floor]

Months ago I noticed when I took off the fuel cap on my Mustang that a lot of air came rushing out of the fuel keck as I spun off the cap. I thought it was a fluke at first but it's not. It's everytime. It doesn't seem to affect the way it drives but I can't think what would cause this problem given that the system is an engine driven mechanical fuel pump. The car is generally stock and I have probably put 1800 miles on it so I'm still learning it.

Tonight I took it on a 10 min drive with 3/4 tank and just as a test when I got home opened the fuel cap.... WHOOSH.

Any ideas on what to look at? Is this a problem or a feature?

[erratic50]

Fuel tank vent tube is plugged. It’s supposed to vent into a charcoal canister that sucks the fumes back into the motor I believe.

could always get a vented gas cap unless it’s an emissions thing where you live

[foot2floor]

What application could I buy a vented cap for which would thread onto the Mustang filler neck?

[Mgino757]

Mine had that same problem. Lo and behold, the evaporative system was not hooked up at all. Ever since I got that system working again, I have not had any problems since. My garage smells a lot better too. I don't know why people screw with disabling this stuff. It doesn't hurt performance any at all.

[MOOSH]

I have tried finding a vented cap and the McParts stores don't seem to carry them. I have read somewhere on the forums here that all you really need is to get a charcoal canister from basically anything and hook up the vent hose to it and problem solved. Thats what I plan to do soon.

[erratic50]

I believe the 80’s VW caps fit and are vented. Don’t remember for sure, but they are available.

charcoal canister is much better route.

[quickshift]

I had the same issue on my F350 460 CC with dual tanks. I just drilled a 1/16" hole in the caps and problem solved.

[ashley roachclip]

Oddly , I have not had said charcoal canister for 20 plus years , and do not have the tank pressure, nor the gas smell .
You have a pinched line .
Fi d that first .
I do agree there is no need to remove the evap. System, but if it is gone , it is rarely cost effective to find and reinstall , if you are not required to have it for emissions in your jurisdiction.

[MOOSH]

My car is also without the trio of solenoid valves that control the emissions stuff. So I am stuck with a vent line that run from the tank to a hard plastic line under the hood. If I put a vacuum cap on it, Smell goes away, but pressure builds in the tank.

go without the cap, no pressure in the tank, but the whole house smells like a gas station.

[swearint]

My car is also without the trio of solenoid valves that control the emissions stuff. So I am stuck with a vent line that run from the tank to a hard plastic line under the hood. If I put a vacuum cap on it, Smell goes away, but pressure builds in the tank.

go without the cap, no pressure in the tank, but the whole house smells like a gas station.

Could you use one of those charcoal ice maker filters? Run the line to the filter and let it vent from there.

[Saturn V]

Could you use one of those charcoal ice maker filters? Run the line to the filter and let it vent from there.

Running the vapor into any charcoal filter will do no good unless the vapors are sucked out, like erratic said. Eventually the charcoal will be saturated with liquid gasoline, if the filter is not purged. The charcoal canister is just a place to trap the vapors temporarily until they can be sucked back into the engine via the purge control valve arrangement.

[gr79]

Ice maker plastic may not be fuel vapor proof?
Salvage or pic a part yards have smog cans with purge valves 10-20 bucks.
One from year 85 Ford prob has combo of connectors needed.
Check entire plastic line for cracks. If found, cut out bad and splice with 1" of rubber vac hose.