‘71 Bronco - excessive gas smell

[71BroncoSean]

Hi all! I have a ‘71 bronco that’s been fully restored. I put a 347 Stroker in her and opted for the larger fuel tank as a result. I got her back from the builder about a year ago and my garage has smelled like gas ever since. My wife is now complaining, so I need to figure out what is going on.

At first I thought it was a function of over-filling the tank, but it doesn’t go away…even when the tank is low. One day I came home from the gas station and parked in the driveway. I live in Florida and the sun is hot. After sitting for an hour or so, I noticed gas coming out of the tank and streaming down the side of the car, which did a number on my paint. So, my question is, am I missing a valve or something that would minimize the fumes and not allow the gas to bubble back up and out of the fuel filler? Thanks for any advice!

 

[DirtDonk]

First thing is you need to make sure you have a charcoal canister system connected to the tank. The tanks have to vent.

Second, what kind of tank is it? If you don’t know take pictures of it so we can see.

And third, no matter what type it is and no matter whether it’s vented or not, try not to top it off. Most bronco tanks don’t have sufficient expansion volume above the fill level. And even when they do we tend to still try to max it out. I still have trouble trying to remember to stop filling mine when I think it gets close. Problem is they fill inconsistently so it’s hard to always know.
Is yours easy to fill, or not?

Topping them off is great in the interest of trying to get to the maximum capacity. Great for miles on the road and trail, not so great for evaporative emissions.

 

[71BroncoSean]

Thanks for the response! I do my best not to top it off. In fact, I stop filling when I think it 90%. As for the tank, it is a "M1A1 Stainless Tank 23 GAL with in-tank High Pressure Pump & Strap Mount" from Wild Horses. I'll look into whether or not I have a charcoal canister system.

 

[DirtDonk]

Great, thanks for the support. A good practice too, going only 90% (or so-ish) at fillup.
A little harder to check for venting than a stock tank, but should be worth a minute or two bent over with a flashlight to see how the installer did it.

Look for the recessed area at the top/front of the tank and for three distinct hoses. If there are three, the one closest to the driver's side is your vent line. If the installer went with the "cap it off if no vent desired" option, then you will want to add one.
Another thing to do I think would be to get under the vehicle, reach up to the hose/module/sender area and run a clean finger around the area to see if there is any gas laying on top of the tank. If the unit was not sealed properly you could be getting some leakage up top when the tank is near full. And certainly when full!

Whether you have that third hose or not, next you can look around for a charcoal canister / EVAP system. Your '71 would originally have come with the early two-part style, with a metal charcoal canister mounted to the passenger side frame rail just to the rear of the front wheel opening. The second part was a plastic condensing tank up behind the driver's left shoulder behind a metal panel.

And speaking of the condensing tank... Had you driven this Bronco extensively before the new tank? If not, you might also be suffering another well-known problem with the early design. The plastic tank may just have given up the ghost and split it's seam. My '71 did this many years ago and since replacements did not exist (and may still not?) I sealed the top seam with good old Form-a-Gasket sticky stuff and got rid of the problem that way.
If your system was intact, and the installer re-used it, then that may actually be the issue.

So check for the existence of that stuff and let us know what you find.

Good luck!

Paul

 

[ksbronco75]

DirtDonk knows his stuff. Take his advice. I had a similar problem and my tank was leaking and evaporating before I could see it, but still smell it. I have a 75 and the PO cut the charcoal canister lines. I replaced the O-Ring in my tank and put little filters on the vent lines connected to the canister. Haven’t had an issue since. That’s just a cheap temp fix. DirtDonk has the permanent fix

 

[armynavy17]

Even if you do have an intact condensing tank behind the driver's seat, I'd recommend converting to the newer style charcoal canister set-up. I've never been a fan of having gasoline in the cab and that doubles when the part is known to fail whether due to splitting the seam or otherwise.