Trying to fire my LS engine for the first time and running into some issues. When trying to put gas in the LS1 tank (plastic style), the gas comes pouring back out of the neck unless I go VERRRY slowly. I'm assuming it's a venting issue and hoping someone can help me fix this.
I installed this tank a couple years ago. My memory is a little fuzzy but I'm pretty sure I left all the vents, tubing and charcoal box on the tank. My car no longer has the charcoal canister in the engine bay so nothing on the LS1 tank is connected to anything else on the car - only the supply and return fuel lines up to the engine and obviously the filler neck. Most of the threads I found on TGO talk about retaining the EVAP and utilizing the factory thirdgen charcoal canister but I don't have either of those.
Can this issue be fixed by adding the thirdgen vent (the one near the rear wheels) to the LS1 tank tubing somehow? I found one thread on LS1tech where a guy added a hose from the tank up to the filler neck to act as a vent. I haven't seen any threads on TGO mentioning this so hopefully I can solve the issue with something less involved.
Here's a picture I found on TGO. If someone could describe how to modify the factory plastic tubes for my situation, that would be awesome.

 

The stock ls1 tank, hoses, and canister should allow for enough venting to fuel up. If its not filling up, you need to drop the tank and make sure thats stuff is there still. I ended up taking all that off years ago when I did my swap only to have the same problem. Of course I didnt have any of the hoses or tank I threw away so I ended up with a new tank off ebay with all the parts and its perfectly fine now.

 

This is absolutely a pressure differential issue.

As Fuel needs to have a flow path into the Tank...
Air needs a flow path out of the Tank, in order to maintain the equilibrium.

You most likely have the Vent Valve Solenoid stuck closed.

 

you have something stuck in the wrong position/ closed, could be the roll over check valve, anti siphon valve, etc... with the pump out of the tank you check all these by putting your hand in the tank and moving them to the right position if they are not

 

i've been trying to read a ton about the EVAP and venting on these tanks. i'm seeing the EVAP and venting on the LS tank were controlled by the factory ECU with input from the 4thgen fuel gauge?? so even if i do have all of those hoses still connected on the tank i installed, won't i still have issues with venting since nothing is telling the parts to open / close? i could be misunderstanding - some of this stuff is over my head. unfortunately this is one of three issues i need to overcome before finally fire my motor.

 

you don't need to control anything to the tank if everything is working correct mechanically, ie non of the roll-overs stuck or vent valve stuck, etc

i have used these tanks on many swaps and they work great. you have something mechanically stuck in the vent circuit

 

I think the native state of the charcoal canister is valve open so it acts as a filter without any wires hooked up. I never smell gas fumes with car sitting in the garage.

 

Correct.

The Solenoid (Vent Valve) is commanded closed when powered; and it is open at rest.
...thus the most likely event to have taken place, is that the Solenoid got stuck closed and did not ReOpen as the corresponding Circuit was powered off.

 

So if he powers the solenoid up and down a few times with a small battery and starts to hear the solenoid clicking, then that might be a quick & free fix with a bit of luck?

Honestly, it doesn't even have to work, the solenoid plunger just has to retract 1 time and it will stay there for life, right? Solenoid on bench, can of carb cleaner, hammer..... Jeremy Clarkson style (Top Gear)

 

If you removed that valve (yellow arrow) and capped that port. That will cause it. I found that out the hard way, re-installed it and all was good. As mentioned it should be open by default.

 

May seem a little overkill but it helped noticeably for me is on that valve there is a foam filter element covering the port. My tank seemed to have come from a super dusty environment because that element on mine was pretty much completely clogged. Take it off, wash it in some soapy water, dry it, and reinstall. Before cleaning I could not fill my tank full flow from the nozzle. I had to use the slowest setting. After, any fille rate worked.

M

 

Awesome - thanks for all the input everyone. I'm hoping to drop the tank maybe next week to check things out.

 

When I installed my tank I had the same issue. I found the check valve on the tank inlet stuck shut. The one just inside the tank - not the one in the filler hose. Before dropping tank - pull filler hose and take a longer screwdriver etc and put it into tank inlet about 4-6". Mine stopped at check valve and I gave slight pressure to pop it loose. No problem since.

Hopefully this helps you from dropping the whole tank. Good luck.

 

I had to drop my fuel tank since the float arm came off of the fuel level sender and I found this check valve in the bottom of the tank with the float. I can not find any reference as to what it is, but it snaps into the white cap from the bottom and inside of the tank, I assume it’s the roll over check valve. My question is, can this be eliminated by removing the hose and capping it? The last couple of times I filled the tank there was a fuel spill, which leads me to believe that is when the valve came off. I do not know if this is an auxiliary tank vent, or if it is needed. Any insight would be appreciated.

 

I ran some tests and I determined that the mystery valve is not needed to vent the tank, so it was capped off. I also removed the purge valve next to the charcoal canister and capped that fitting on the canister. The fuel module vent and the charcoal vent are more than adequate for the tank to function properly.