Pressurized FJ55 gas tank (1 Viewer)

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Dec 24, 2012
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Location
Chatham NJ
I turned the truck on last weekend, filled it up and took for a ride. once i entered the garage i heard a hissing out of the gas cap...pressure! i would like to see if my thinking is correct about how the venting will be fixed. I made sure the evaporator was free and clear. removed the broken/clogged check valve at the top of the unit. used that line that ran directly to the engine bay and put a FJ80 Charcoal canister up there. so the lines go like this... 4 from tank to evaporator separator; line at top of evap sep to "tank" side of charcoal canister. Now my gas cap reads "vacuum pressure" so to test my theory i took off a line and used my mouth the pressurize the tank. it built pressure and did not release it. moved the hose "from tank" to the "purge" port on the canister all is well but should i leave it like that? if enough force it applied to the "from tank" it opens up just not free flowing like the "purge" port.
 
Capped the “from tank” port and put it on the purge port because I have no emissions.
 
The purge port is free flowing because usually there is a fresh air vent for the purge line. When the system is purged, you don't want that vacuum being applied to your tank and pulling liquid fuel out. The From Tank line should be one way - vapors check in, but they don't check out. When your tank, and all the fuel in it cools, the system is supposed to pull air in from the fuel cap. The gas cap should also be a one way valve, it will let fresh air into the tank, but it should not let gas vapors out. Does that make sense?

Check your air flow from the evap line at the charcoal canister to the rear. It may be that the 80 series can requires too much pressure to open and your cap is leaking at the worn out fuel neck...

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I’m just letting the tank vent through the purge port

How are you evacuating the gas fumes from the can?
You need to pull those fumes into the engine and burn them. Otherwise you will have a not-so-pleasant raw fuel filtered by charcoal smell in the engine bay and probably in the passenger compartment.
Make sense?
 
Reviving this, after searching. Truck was sitting for years before recent work. I have fuel smell in the cab, which has always been there since purchase 7yrs ago, but seems worse now. and after having extensive carb work done at Classic Cruisers, truck was running great. I stopped to put gas in, on the way home from the shop (35 miles) and it was pressurized….which I was used to it always did that. Upon closing up the cap & pulling away, the truck stuttered a bit getting up to highway speeds. Then was fine the rest of the drive. My thought was the tank ended up with some negative pressure and starved fuel a tiny bit during heavy acceleration onto the highway? The truck ran great in every other situation, just the hiccups for 1st acceleration after fueling. Lol….dang near got rear ended, Colorado folks is in a rush these days I reckon!
I think I’m gonna start with a new gas cap, eliminate the check valve above the vapor separator, and POSSIBLY try to retrofit a charcoal canister from something else if I can find something similar enuff.
The gas smell is annoying, the stutter is dangerous, tho.
I’ve read the fuel breather symptoms are fairly common, So I wanted to ask 2 questions. Anyone else had anything similar happen? What are the workarounds?
 
There area few iterations of gas tanks with different venting methods. I think they all are an issue if you dont have all of the OEM parts still. @J Mack gave me the best advice for my fuel tank and I think it can work for a stock tank too. Plug all the existing vent tubes, drill a hole in the top, probably near the sending unit and put a screw on a 3/8 fitting and get like 8 feet of fuel line. Wrap the line in a coil over the tank. Drill a hole in the fuel door area and have it VTA. If you are worried about gas smell, buy one of those $20 inline charcoal filters. I did all of that except the filter part and I never have issues now.
 
There area few iterations of gas tanks with different venting methods. I think they all are an issue if you dont have all of the OEM parts still. @J Mack gave me the best advice for my fuel tank and I think it can work for a stock tank too. Plug all the existing vent tubes, drill a hole in the top, probably near the sending unit and put a screw on a 3/8 fitting and get like 8 feet of fuel line. Wrap the line in a coil over the tank. Drill a hole in the fuel door area and have it VTA. If you are worried about gas smell, buy one of those $20 inline charcoal filters. I did all of that except the filter part and I never have issues now.
Phenomal info & Mega awesome advice, Brutha! Pershiate ya takin the time to describe your setup. I may take that route once I open everything up. Drove the rig around town all day w no hiccups, but winter is coming so I’m in scramble mode to dial in all the glitches before I’m in “windows up” mode for 6 months 😂
Thanx man…..hey, You still rollin in the same rig you had in ‘17 when we met in Rico CO?
 
Reviving this, after searching. Truck was sitting for years before recent work. I have fuel smell in the cab, which has always been there since purchase 7yrs ago, but seems worse now. and after having extensive carb work done at Classic Cruisers, truck was running great. I stopped to put gas in, on the way home from the shop (35 miles) and it was pressurized….which I was used to it always did that. Upon closing up the cap & pulling away, the truck stuttered a bit getting up to highway speeds. Then was fine the rest of the drive. My thought was the tank ended up with some negative pressure and starved fuel a tiny bit during heavy acceleration onto the highway? The truck ran great in every other situation, just the hiccups for 1st acceleration after fueling. Lol….dang near got rear ended, Colorado folks is in a rush these days I reckon!
I think I’m gonna start with a new gas cap, eliminate the check valve above the vapor separator, and POSSIBLY try to retrofit a charcoal canister from something else if I can find something similar enuff.
The gas smell is annoying, the stutter is dangerous, tho.
I’ve read the fuel breather symptoms are fairly common, So I wanted to ask 2 questions. Anyone else had anything similar happen? What are the workarounds?
I don't remember your set-up, and how you are handling vapors from the tank currently?

If you are just going to vent to atmosphere, I am not going to bother writing a lot of words.
 
I don't remember your set-up, and how you are handling vapors from the tank currently?

If you are just going to vent to atmosphere, I am not going to bother writing a lot of words.
I’m running pretty much a bone stock ‘76.
My vapor system is in place, stock & prolly a 47yr old pile of crumbling plastic. 🤣
I think you and others have explained it pretty good, tho. I can fab up a good chunk of replacement tubes, connections and paths, and I think I can dial it in.
The truck smells real gassy…..but has run amazingly and I can’t replicate the brief minor stumbling I had after picking it up and running it the first time….
Gonna fire up the air compressor for checking lines & valves.
You’ve posted a ton of good advice on this, I’ll try all that first and report back.
Thnx again!!
 
I’m running pretty much a bone stock ‘76.
My vapor system is in place, stock & prolly a 47yr old pile of crumbling plastic. 🤣
I think you and others have explained it pretty good, tho. I can fab up a good chunk of replacement tubes, connections and paths, and I think I can dial it in.
The truck smells real gassy…..but has run amazingly and I can’t replicate the brief minor stumbling I had after picking it up and running it the first time….
Gonna fire up the air compressor for checking lines & valves.
You’ve posted a ton of good advice on this, I’ll try all that first and report back.
Thnx again!!
Good luck!
It is always nice when you can park your Pig indoors and it doesn't smell like gas after a few minutes.
 

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