Gas tank vent tube

[72gmcshorty]

How does the vent tube actually work? I am going to fuel injection and have a new tank. Do i still need to hook this thing up again?

[Firebirdjones]

The gas tank vent originally runs through the charcoal cannister which is originally mounted behind the battery. It's controlled by a vacuum switch that works through ported manifold vacuum only, meaning it activates when the throttle blades are cracked open.

The issue with this is that most fuel injected setups don't have a ported vacuum source unless you are using a throttle body style setup that might have a ported vacuum connection.

I'm running a 6.0 LS. The LS style fuel injected engines don't have a ported vacuum source which rendered my charcoal cannister useless. I had to switch to a vented gas cap as a simple solution. That's one option for you.

Without the tank vented, you run the risk of overheating or burning up the electric fuel pump required for fuel injection, which kills the lifespan, or you can have fluctuating fuel pressure readings, gas tanks that expand and contract, among other things.
So you'll have to find a way to vent the tank if you can't use your charcoal cannister.

[72gmcshorty]

the tank i'm using has many vents, what do i do?

[Firebirdjones]

2 of those lines are fuel supply and return, which it appears you have hooked up already.

That third line capped off would be meant for the vapor vent or tank vent and would run up to the charcoal cannister.
The other 2 lines on the charcoal cannister, the larger one would "T" into the PCV valve, and the small port is for ported (switched) manifold vacuum.

Not sure what fuel injection you are running, but you may or may not have a switched vacuum source in front of the throttle blade.

If not you would have to come up with another option for that vented fuel line at the tank. Either run a hose with a filter on the end of it, and put it up higher than the tank. Possibly run it along the filler neck? So long as it's kept outside the truck since it is a possible fume hazzard.
Or,,,,you could simply run a vented gas cap and cap off the other ports on the gas tank...

[72gmcshorty]

I plan on using a 2006 LS truck motor. If I use a vented gas neck, what do i do with the two vents on the sending unit? I am trying not to use a charcoal canister...

[Firebirdjones]

One of those larger connections that appear to be either 1/2" or 5/8" is probably meant for the overflow tube that connects to your filler neck. Mine has an overflow tube (or filler vent) that connects to the top of the filler neck and it's about that size.

So you have your fuel supply and return, possibly an extra filler neck tube of 1/2" or 5/8", then you can use the other small tube coming out of the sending unit (which appears to be 1/4") for a vent hose if you wish (so you are venting at the very top of the tank), or use a vented gas cap since you don't wish to use the charcoal cannister.

The rest would simply be capped off. That's how I have mine setup running a 6.0 LS engine. Works excellent.