EFI and Gas Tank Vents?

[duffymahoney]

Hello All,

This might be a dumb question, but do gas tanks need to have separate vents or can you use a vented gas cap? I am doing the 5.0 swap and I would really like to use the 77 stock vent location as my return gas inlet for the EFI. I believe my modern cars all have pressurized gas tanks? Is there a reason for that? Also , my stock aux tank has no vent. If I have to have a vent, can I can add a vent like this one?

http://shop.broncograveyard.com/197...ck-Gas-Tank-Breather-Valve/productinfo/20241/

Sorry this is all a little confusing!

 

[ScanmanSteven]

I'm going to say no. Dumb answer huh? I have EFI so I'll answer with my experience. If you're going off road you don't want a vented cap because of leakage when on hills. I don't think you are, looks like you're building a street rig, I didn't look at your build, just guessing from your signature line. So if you use a vented cap you should be able to run the return line to the vent and be okay with the dual use. The 76-77 came with unvented caps (I think) because of emissions, that's why they had the evaporator tank behind the drivers seat that then ran to the charcoal filter then to the carb. I forgot to look where you live so as long as you don't need emissions testing you should be able to double use the vent. As for the auxiliary tank, it needs to be vented if you run a return line to it because some of the hot fuel returning will vaporize and you need to vent it. Hope this helps, I'm sure others will correct if I'm off on my assessment.

 

[spap]

It needs to be vented, kinda depends on smog laws and I don't you have any trouble with those in ID. A cap would work

 

[duffymahoney]

ID= zero smog laws

I plan on running my return line to the main tank (not the aux), then just using the aux tanks for long hauls- road trip, but most of the time it would be empty. It will be a street rig 90%, then hunting, fishing, camping, skiing etc.. I was planning on venting both with caps.

 

[garberz]

I don't have a vent for my EFI, I vented the cap with an 1/8" drill bit. I thought it would leak on the trail, but it's good. The downside is the garage smells a bit. You'd need a charcoal canister to get rid of that.

Mark

 

[Viperwolf1]

I believe the vent ports at the tanks have very small orifices to try and keep liquid fuel out of the vent system. When I say small I mean something around .060". I bet you can't push fuel through it very fast.

 

[duffymahoney]

I removed the old return insert. It had tiny holes in it. Now it's A full stainless hose barb. Thoughts on just adding a vent? Then running it go the intake of a charcoal canister?

 

[Rox Crusher]

It needs to be vented or the hot fuel returning from engine will create excess pressure.

I was having this problem and discovered that my vent line had gotten pinched closed as the body mounts settled.

 

[spap]

I always thought that a good place for a vent is to drill a small hole into the top of top of the sending unit and braze in a small piece of tube that has a 90 degree angle to it and hook the vent line to that
i was going to do that but got a 23 gal efi tank instead

 

[ntsqd]

Put the return in the filler neck somewhere above the full fuel level.

Vent the aux tank(s) to the main tank, and vent it. On my old dune buggy I put the vent fitting in the fill neck *right* under the sealed cap. Ran a hose off of it down a ways where if it did spew a little it wouldn't be landing on paint or smelling bad under my nose. I put a cheap plastic fuel filter in the end of the vent hose.

 

[EBGeek]

Duffy - sorry if this is a hijack, but it seems you're at a place similar to me.

Viperwolf - you mentioned the vent lines are only .060 to keep fuel out of the vent system. Do you think that could be causing my EFI return line (that I ran to one of my vent nipples on the stock tank) to push fuel out the adjacent vent line? It was my intent to hook up my vent line to a charcoal canister, but I can't get to that point until I can keep my vent line from puking while the engine is running.

My thread about it:
http://classicbroncos.com/forums/showthread.php?t=259025

 

[duffymahoney]

Ok, I plan on doing the return line to the vent location. Not T'ing into it. Then on the fill vent I will do a T to a charcoal canister. That way the tank can breath, and I won't get fumes. Same for the Aux tank. Does that make sense?

 

[duffymahoney]

Duffy - sorry if this is a hijack, but it seems you're at a place similar to me.

Viperwolf - you mentioned the vent lines are only .060 to keep fuel out of the vent system. Do you think that could be causing my EFI return line (that I ran to one of my vent nipples on the stock tank) to push fuel out the adjacent vent line? It was my intent to hook up my vent line to a charcoal canister, but I can't get to that point until I can keep my vent line from puking while the engine is running.

My thread about it:
http://classicbroncos.com/forums/showthread.php?t=259025

I'm guessing you need to remove the stock vent from the tank and install a stainless or brass hose barb fitting. The small holes in the vent fitting would make it hard for gas to pass through it, thus causing it to run up the vent line and dump out while the engine is running.

 

[ntsqd]

If the vent port has a restriction in it why do you want to return to it? Use the vent port for a vent (charcoal canister or otherwise) and put the return somewhere else.

I'm going to put the return in the fill neck about 4"-6" below the cap. Simple to drill and tap NPT threads then screw in a 90° fitting with some sealant. Or like I plan to do, silver-solder an NPT bung to the fill neck for the return.