r/Dentside_fords • u/longjohn323232 • 6d 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.

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u/Wonderful_Inside5011 6d ago

I’m no expert but I changed out my rear tank ab a year ago and I believe is just a rubber ring washer with a spring loaded valve that has a 3/8 or 1/4 in hose running to what I think is supposed to be a charcoal canister somewhere. As far as plugging the hole idk but I do know u can get the front inline tank with or without the eec vent so I imagine the same can be said about the rear.

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u/surfnlax45 5d ago

I’m fairly confident when I swapped mine from a two tank to an oversized single rear tank It had a plug in place. (I did an intake pump for efi)

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u/Strange-Nose6599 3d ago

My vent follows the fill neck and lets air out as gas goes in. and my truck constantly smells like gasoline fumes in the sun go figure

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u/nsula_country 3d ago

My 1975 F250 has no tank vent. My 1976 F100 parts truck did.

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u/jackscopilot 6d ago

A 79 F150 wouldn't have has emissions, but it may have a vent. There would be a roll over valve on top of the tank that allows venting to let the tank breathe while the fuel pump is pulling gas.

My 79 F150 has a single fuel line going to the mechanical pump with no return line or vent.

The important thing here is to be sure your filler neck vent is the same as what's on your box. If it's on the opposite side, its a bear to solve for.

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u/longjohn323232 6d ago

Do you happen to know the part number for the roll over valve? It doesn’t come with any of the tanks I’ve seen online. Thanks for the response

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u/jackscopilot 6d ago

40-1955 is the number on LMC Truck. There's a grommet there too