s14 factory fuel tank ventilation - the 3rd hard line

[s14unimog]

So I'm in the process of putting my car back together and would like to clean up the fuel lines as they enter the engine bay. Originally there are 3 hard lines (feed, return, ventilation), my question pertains to that vent line. For years I've run with that line just left open to atmosphere and never had any issues with my tank, fuel pressure, gassy smells, etc... so I assumed it hasn't been hurtful to the operation of the tank ventilation.

So my question is what exactly does that hard line do for the tank? If I can recall, I wanted to say it was supposed to be for ventilating fuel smell into a canister to suppress the odor but most of my OEM stuff is long gone and I don't have any fuel odors . Does anyone have any experience with the OEM tank assembly/functionality that could shed some light on what you should/shouldn't do in respect to ventilation?

Thanks!

[mushmonster]

that line does indeed go to the charcoal canister and its to collect fuel vapor. you can cut it all the way back to the tank add a rubber hose coiled 2 or 3 times and mount it high above the tank. correct me if im wrong zilvia, I was going to keep it this way untill i install a fuel cell. I know that some fuel cells have one or more breathers with a roll over valve.

[s14unimog]

Are the additional coils you mentioned to protect from over flow slosh with a full tank? Does is also involve the canister located in the passenger side rear fender well? There are number of vacuum lines going to this but I haven't looked closely at it.

What is strange is that this topic seems untouched within the Zilvia archives

[s14unimog]

Bump to the top... Anyone other experiences?

[KiLLeR2001]

Not sure if I would leave it fully open. On the s13 there is a 2-way valve in-line with the ventilation line. When gas leaves the tank this valve sucks in air (as well as the gas gap). And most importantly, when pressure is too great it'll release vapors out of the ventilation line.

I would think if you just let it open, gas would evaporate quicker and you will have to fill up more frequently. Not to mention if your tank is metal and moisture enters, rust will form.

S13: http://www.courtesyparts.com/17330-valve-assy-fuel-check-240sx-s13-1989-1994-p-65084.html
S14: http://www.courtesyparts.com/17370-valve-assy-check-240sx-s14-1995-1998-p-185107.html

[s14unimog]

Thanks for the links, I wonder where they're mounted on the chassis; I'll have to get under there and look. As for the tank, it's an OEM unit so that's plastic.

[92lt1]

i would like to know as well, i just did a small block chevy swap and right now just have the line open in the engine bay

[codyace]

I use the line to house wires for the meth pump and 2nd fuel pump. Don't even worry about it. Tank still holds pressure as it releases when I fill it up.

[s14unimog]

^ I'm not exactly "worried" about it but rather looking at how its placement/routing plays a roll in the tank's operation. Once I get done with my tubs I'll really dissect it but I was hoping others have dealt with this and can shed some light on it. I don't like unnecessary parts on the car.

[codyace]

It comes out of the rear vent deal in the back passenger corner of our cars I'm almost positive, as above I simply cut it, and then ran my wires through it to help protect them...it was a mofugga to get them through but it did work.

[jr_ss]

It comes out of the rear vent deal in the back passenger corner of our cars I'm almost positive, as above I simply cut it, and then ran my wires through it to help protect them...it was a mofugga to get them through but it did work.

Should've used some electricians string and a vacuum to suck it through the line. However, that is a great way to run wires front to back or vice versa...

I'm about to remove the vent line and my factory feed for my -6an fuel lines. I'll probably run the vent up to the fuel filler neck and tie it in there...

[codyace]

Should've used some electricians string and a vacuum to suck it through the line. However, that is a great way to run wires front to back or vice versa...

I'm about to remove the vent line and my factory feed for my -6an fuel lines. I'll probably run the vent up to the fuel filler neck and tie it in there...

That's exactly what I did, but after 3 wires (fuel pump rewire, meth pump wire, and wire for 2nd pump) it became a little tight (albiet worked) A little synthetic lube goes a long way with that stuff.

[s14unimog]

So it does run into that canister in the back passenger side corner? Once I get the car back at the house this weekend, I'm going to crawl under there and get it sorted. Silicone lube can really help in a tight spot.

[codyace]

Offtopic: We use this stuff called SuperLube at the shop, really works well.

[jr_ss]

Offtopic: We use this stuff called SuperLube at the shop, really works well.

You can find the lube at Lowe's in the electrical section. Stuff is super slick and water soluble...

[s14unimog]

Okay, Silicone lube covered.... Let's try and stay on topic. I brought my car back from the shop last night so I'll finally get a chance to get back under it.

[jr_ss]

Okay, Silicone lube covered.... Let's try and stay on topic. I brought my car back from the shop last night so I'll finally get a chance to get back under it.

I need to crawl under mine as well. I need to pull the lines out to have the bay painted anyway. I'd like to remove the feed line and vent line altogether, I'll be running a -6AN line for feed and using the factory return.

[s14unimog]

^same here, I just got my tubs finished but had to do it up at my work; for the welding equipment. Now that I've got it back at the house i've got to get the bay stripped for painting; I might as well ditch that line if I'm not using it.

I'll let ya know what I figure out.

[s14unimog]

just to update, I finally found some information in my 240SX FSM in the extensive trouble shooting section. I will post pictures of the page referencing the charcoal canister but that little box in the back is only there to help eliminate fumes emitted from the tank. That vacuum line (or third hard line in the engine bay) is what facilitates the vacuum to draw fumes into the canister; it actually runs through a check valve to prevent un-metered air from entering the engine. Actually there are provisions for checking its operation, as well as the fuel cap. It does seem tho, that you can eliminate that entire assembly as the fuel cap (If an OEM unit) is pressure and vacuum rated; so the fuel cap should prevent any excessive build up of pressure or negative pressure in the tank; plus the tank has a separate overflow line to the filler neck. I will trace the lines out on my car and clarify Nissan's wording a little.

[KiLLeR2001]

It does seem tho, that you can eliminate that entire assembly as the fuel cap (If an OEM unit) is pressure and vacuum rated; so the fuel cap should prevent any excessive build up of pressure or negative pressure in the tank; plus the tank has a separate overflow line to the filler neck. I will trace the lines out on my car and clarify Nissan's wording a little.

Negative. The OEM fuel cap is vacuum rated ONLY. It WILL NOT release excess pressure build up (unless you unscrew it of course). The fuel check valve that is in-line with the ventilation line acts as a two-way valve. It's clearly illustrated in the FSM (see EF & EC 194).

[s14unimog]

I'll show you the excerpt I'm referencing from the FSM trouble shooting guide but it clearly says that it is both vacuum and pressure rated, no lie. My first notion was that it can't be as we're all very familiar with the pressure release when unscrewing the cap but I assure you its clearly stated in the FSM; that's why I said I wanted to test mine and it has to be an OEM unit.

Also note, there are multiple check valves related to this charcoal ventilation system. I'll post the section I'm in. I looked at it last night and just left my book open on my desk. This is a good discussion though, and a worthwhile topic to hash out.

[KiLLeR2001]

Maybe the S14 is different. I'm talking about the S13... lol

[s14unimog]

well shit man, you're muddying the water; lol. Surely they're the same.

[KiLLeR2001]

Here's the page from the S13 FSM...

http://tehl33tsite.com/240sxdd/help/ecef194.jpg

As you can clearly see, illustration #1 (gas cap) only allows vacuum. And illustration #2 (fuel check valve) shows vacuum and pressure arrows. Black displays pressure and white displays vacuum.

[s14unimog]

Well that's official, they are different. B/C it clearly states that it is both vacuum and pressure rated in the S14 FSM. I'll post a picture tonight.

[KiLLeR2001]

I see, for the S14 go here...

http://www.240edge.com/manuals/95_240sx/ec.pdf

Scroll down to page 19. It appears the S14 gas cap is two-way. So essentially you could eliminate the check valve, but I would think it would be more smooth of an operation if the gas cap sucks in air and the check valve releases air.

[s14unimog]

^ Ya, I've got the digital format on my home computer. But ya, I think you are correct. The only issue is that that check valve (the one I think you are referring to) is located in the engine bay and usually gets tossed along with the vacuum assembly at the motor. I haven't looked under the car but I assume the next one in line is actually internal on that canister.


EDIT: you know what, the FSM I have is actually for a 97' (mine is a 96') and they are actually different between the two (more likely OBDI & OBDII). I will post the assembly my book shows but you bring up a good point, I bet the "fuel check valve" or "vacuum check valve" (as its called in the 97 FSM) would be more reliable to handle positive pressure release.

2nd Edit: Here are those pictures. It seems as though they both have that check valve on the tank ventilation line, although their assemblies are slightly different. So retaining that and having an operational fuel cap with confirmed vacuum operation should allow you to delete that canister and the "3rd hard line." Anyone have any objections?

http://img.photobucket.com/albums/v721/s14unimog/FuelTankVentilation-FSM001.jpg

http://img.photobucket.com/albums/v721/s14unimog/FuelTankVentilation-FSM002.jpg

[jr_ss]

Throw that 3rd hardline in the trash, mine is on it's way...

[Options13]

sooo... can you delete this hardline or not?

[codyace]

sooo... can you delete this hardline or not?

Yes you can.

[cured13]

to make it clear,
after cutting off the hard lne and Charcoal Canister on s13
the Fuel Filller Cap should be upgraded to the s14 one?

I just don't want to burn in flames when my car rolls over and fuel leaks through that cap also don't want to kill the fuel pump fighting to pump fuel in normal operation.

[Mikester]

to make it clear,
after cutting off the hard lne and Charcoal Canister on s13
the Fuel Filller Cap should be upgraded to the s14 one?

I just don't want to burn in flames when my car rolls over and fuel leaks through that cap also don't want to kill the fuel pump fighting to pump fuel in normal operation.

http://zilvia.net/f/s-chassis/503574-how-delete-s13-charcoal-cannister-evap-system.html

I got a good laugh out of re-reading that thread- Killer2001 is a very smart, passionate guy haha!

An S14 cap will be good once the rest of the system is deleted. However, with the top (original evap) line vented to atmosphere, it is not completely necessary. The key is that the tank needs to 'breathe' so as not to overpressurize with fumes or implode due to excessive back-pressure.

You had mentioned 'burning to death in the event of a rollover... Not very likely due to the location of the vent. Also, without a roll cage, fuel leaking from the top of the tank during rollover would probably be the least of your immediate worries ;)

I still have not gotten an S14 cap... but my S13 is not a daily driver & spends much of its life in the garage under a cover. An S14 cap would be MUCH more practical if I had the upper evap port completely blocked off.

[jr_ss]

The S14 tank has a "breather" tube that goes back up to the filler neck.

[cured13]

Roll cage is on my list (somewhere at the end of it)
but getting that Charcoal Can and lines off my car is at the top of it.

What other 2-way cap (other than s14) can be used on s13,
anybody tried other Nissans caps?

[Mikester]

Roll cage is on my list (somewhere at the end of it)
but getting that Charcoal Can and lines off my car is at the top of it.

What other 2-way cap (other than s14) can be used on s13,
anybody tried other Nissans caps?

You can awlays Google the part number and see...

However- Why re-invent the wheel? S14 cap does the trick... and plugs & plays... and is probably the very same part # across a zillion other 1995+ Nissan models for that very reason.

[KiLLeR2001]

Personally, I would keep both the gas cap (S14) and fuel check valve. If you have an S13 cap, upgrading to the S14 cap should be a given. Any aftermarket gas cap you buy for a 240sx is going to be a two-way. It would be wise to buy OEM however, it has the exact specifications needed for our cars. To me it seems that if you only have the cap doing all the work, it will need to be replaced more often. And I'm not even sure the gas cap alone can keep up with the amount of pressure that needs to be released... I installed an S14 cap on my two-tone and when I go to remove the cap I get a little release of pressure (which seems normal). When I had the S13 cap it was A LOT more air rushing out. This leads me to believe that my fuel check valve may need to be replaced. I am going to replace it soon and will be interested to know if the amount of pressure at the cap changes. I will report back.

[Mikester]

^^Will be interesting to see.

BTW, the infamous S13 'WHOOSH' is usually air rushing in, not out ;)

[KiLLeR2001]

^^Will be interesting to see.

BTW, the infamous S13 'WHOOSH' is usually air rushing in, not out ;)

I find that hard to believe because not only do I feel air pushing onto and around my hand, the smell of fuel is directed outwards. If you are experiencing vacuum when you remove your gas cap then you need to replace the gas cap immediately because it is not working properly. The gas caps' main job is to suck in air from outside when fuel is removed from the tank. A fuel tank that is completely blocked off could either implode (too much vacuum) or explode (too much pressure). Although I would imagine it would take extreme measures for either outcome to happen, the fuel pump would more than likely stop functioning before that.

[Mikester]

I find that hard to believe because not only do I feel air pushing onto and around my hand, the smell of fuel is directed outwards. If you are experiencing vacuum when you remove your gas cap then you need to replace the gas cap immediately because it is not working properly. The gas caps' main job is to suck in air from outside when fuel is removed from the tank. A fuel tank that is completely blocked off could either implode (too much vacuum) or explode (too much pressure). Although I would imagine it would take extreme measures for either outcome to happen, the fuel pump would more than likely stop functioning before that.

Lol tank implosion is a definite possibility if not vented in some way shape or form- seen it happen to a high-hp car w the tank evap completely blocked off. However, with an elec pump in the tank; negative pressure is not a bad thing in moderation. Keeps fumes at bay. Not saying there would NEVER be a rush of air out due to heat, expansion & evaporation; but when regularly driven (S13 w OEM cap), the majority of air pressure will be negative due to pump suction. Not talking a huge amount, but enough just to equalize the pressure.

[Mister.E]

Sorry to revive an older thread, but i needed to get some clarification.

Im planning on buying this Gate's cap to replace my old ass OEM S14 cap: http://www.frsport.com/Gates-31615-Pressure-Vent-Fuel-Cap-Nissan-240SX-4-Cyl--2-4-L_p_29261.html

With a properly operating cap, are people with S14's just blocking off the vent line completely? If not, then what are you doing? i dont want to attach a line and just leave it open to the air, it gets hot as hell here in vegas in the summer and i fear i would get a ton of fuel evaporating and just be wasting gas.