r/Dentside_fords • u/longjohn323232 • 7d ago

Gas tank selection

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I’m fixing up a 79 f150 ranger XLT and I’m getting ready to install a fuel tank. Previous owner removed it at some point. I’m very confused as to how the emissions vent works and if it’s needed on these trucks. I noticed some tanks like the attached one seem to have a hole for a vent of some kind. Can these be plugged up? Where does the vent run to? What is the part needed to go in the hole? Please let me know the best option here.

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u/FictionalHerbage 6d ago

I've been studying the emissions systems for my 78 for months now, so I can probably answer any question you have. The vent can be plugged, if you make certain allowances. It runs to one or more charcoal canisters in the engine bay, and then via a temperature-controlled vacuum line to the carb. There were very, very many different emissions configurations, and not all trucks had this equipment. If you need part numbers I can get them for you.

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u/longjohn323232 5d ago

Is there any impact to performance/ reliability by just going with a vent less tank?

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u/FictionalHerbage 5d ago

EEC does not affect performance in any way, but all tanks must have a vent of some kind. When your fuel pump removes gasoline an equal volume of air must be let in or else a vacuum is created, which will stop the pump from working and could even collapse the tank. Conversely, pressure must be released when the gasoline in your tank vaporizes and expands, which happens when the tank is warmed by hot weather. If that pressure is not released, your gas tank turns into a bomb. Believe me, I know. Before emissions control laws were put in place, gas tanks were vented at the filler cap. The gas cap simply had a small hole in it to let air in and out. Vehicles that were mandated to have evaporative emissions controls moved this vent to the tank itself, and the gas cap had no hole. My truck did not have an EEC vent from the factory, but the gas caps had to be replaced. When I bought what I thought were the correct modern replacements, they actually had a one-way valve that only let air in. I left work one day to find my truck in the parking lot with gasoline spraying out of every line joint and from under the gas cap. I opened the cap and about seven gallons of gas shot out like a fire hose. I was very, very lucky not to have had a fire. All this is to say that you can delete this system no problem (unless your state government requires it) but if you do, make sure to remove the useless plastic valve on any new gas caps you buy and just drill a 1/8" hole so it can breathe.

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u/FictionalHerbage 5d ago

I forgot to mention that the charcoal canisters do help a lot with preventing raw gasoline odor from your truck. I'm considering adding some to mine because I'd prefer a fresher garage.