Should my '79 have a vented or unvented gas cap? I just found through troubleshooting that it runs a lot better at sustained high throttle openings like cruising down the road at 70 mph when the gas cap is removed. That tells me either there is a vent on the tank that is clogged or I have the wrong cap that doesn't vent. Does anyone know which it should be?
cwegga
'79 Gas cap vented or unvented?
1 reading
I think that depends on whether or not you have the hole in the top of your tank for the valve that vents the gas fumes to a charcoal canister.
My 78's tank does not have it nor does it have a charcoal canister or the hardline for one and so the only paths for the gas are out the sending unit or out the fuel filler.
My gas cap is vented due to this and I'm pretty sure it works correctly because when it's hot outside and the pressure in the tank changes due to the ambient temp, I can smell gas fumes by the filler door.
I know some guys on the 73-79 fte forum have had issues with their vented caps not venting properly or not soon enough for their liking (lower pressure level), so they've drilled very very small holes in their cap to allow it to vent freely. I don't know if I'd do that, but it's something I've come across while reading the forums.
Otherwise, if your tank has that valve on the top of it and it has a hardline and charcoal canister, it could be that the system is not functioning properly. The valve could be bad, something could be wrong with the canister, or maybe it's not hooked up to the carb right to draw in the vapors from the canister. 🤷‍♂️
My 78's tank does not have it nor does it have a charcoal canister or the hardline for one and so the only paths for the gas are out the sending unit or out the fuel filler.
My gas cap is vented due to this and I'm pretty sure it works correctly because when it's hot outside and the pressure in the tank changes due to the ambient temp, I can smell gas fumes by the filler door.
I know some guys on the 73-79 fte forum have had issues with their vented caps not venting properly or not soon enough for their liking (lower pressure level), so they've drilled very very small holes in their cap to allow it to vent freely. I don't know if I'd do that, but it's something I've come across while reading the forums.
Otherwise, if your tank has that valve on the top of it and it has a hardline and charcoal canister, it could be that the system is not functioning properly. The valve could be bad, something could be wrong with the canister, or maybe it's not hooked up to the carb right to draw in the vapors from the canister. 🤷‍♂️
The above is correct, or what should be.
Tho all these are so old now its hard to tell what has been swapped around.
In '78, at least in non cali states, the Bronco was a high enough gvwr (higher then f-150) that it didnt neat the full emissions. Therefore it did not have to have all the emissions equipment until 79. Example a 78 would not have had cataylitic convertors either. (Again "Federal" trucks not cali)
My own 78 is one that does not have the extra vent in the tank, it also has the larger gas filler neck, which I like as its easier to put fuel in from racing jugs. It also had the stickers to match under the hood that said non-cataylst or something like that
Tho all these are so old now its hard to tell what has been swapped around.
In '78, at least in non cali states, the Bronco was a high enough gvwr (higher then f-150) that it didnt neat the full emissions. Therefore it did not have to have all the emissions equipment until 79. Example a 78 would not have had cataylitic convertors either. (Again "Federal" trucks not cali)
My own 78 is one that does not have the extra vent in the tank, it also has the larger gas filler neck, which I like as its easier to put fuel in from racing jugs. It also had the stickers to match under the hood that said non-cataylst or something like that
In Arizona, the AZDOT tests the gas caps for leakage. If you have a vented cap, it fails, and they MAKE you get a non-vented cap to pass emissions. So you have to have 2 caps!
And remember, the '79 Bronc was released somewhere around the 4th quarter 1978, I got 1.
And remember, the '79 Bronc was released somewhere around the 4th quarter 1978, I got 1.
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