Looking for some help on this one. It's a 2005 Silverado, I removed the evap entirely but I'm not sure how much that is contributing to my problem. In the first picture is the way that I set it up. I am assuming that the gray ports at the front and rear of the gas tank are just open vents, no check valves. Am I right about that?

In stock form, the front one was setup with a T, going up to the filler neck breather and the other going somewhere to the evap cannister I think. So when I removed that stuff, I just took the front port and the rear port and teed those together, running below the gas tank cross member. Everything was working great until I went to go put gas in the truck. The pump will run nice up until it adds 1.5-ish gallons. Then it turns off, I wait and put in .2 more gallons and it shuts off again. The longer I wait before filling again, the more it's able to get in, but not much. It will take me 10 minutes to do 5 gallons.

This is how I had it.


My friend and I pulled the bed back off tonight to look at it and try to figure something out. What we did find is that there was gas in the T'd line running from the front port to the rear, where it dipped below the cross member in that low spot. So we changed it up and tried running a line above the cross member to eliminate the low spot for the liquid to sit. I went to the gas station... no change.

I came back and we tried something else, added a T inline with the new line we just ran, and vented that one up to the filler neck area also. Basically two vents running in parallel. I ran back to the gas station... still no change. The pump shuts off early. That's how we left it for the night, ran out of time.



Those that have done custom setups, do you see anything wrong here? I never had a problem with it when it was a fully stock pump. If you blow down the filler breather line, it is clear. I did notice that there is a brass orifice in the line up near the filler neck. Maybe that small hole is not allowing enough vapor out?

 

You got rid of the evap port, remember how big that hose was? When you add a liquid to a container, it displaces the air inside it. Gas pumps turn off when they sense a pressure increase from the tank, which is the air trying to get out. You made it too hard for the air to get out. It will fill a little bit at first because you are building pressure in the tank and it slowly equalizes.

I used a 5/8" hose to the evap port (that you got rid of) to a remote filter by the gas cap. Although since I deleted the evap I get a gas smell if I leave it in the garage.

Short version, you need to vent the tank better.

 

Yeah you know when I took it all apart, I didn't know exactly what was what and the purpose of each line. There's so many running around.

I see what you're saying and it makes perfect sense. So I wonder if the two lines I have run right now are still not enough. I'll try removing the brass piece from the stock vent tube tonight and see what that does. It has a really small hole that's probably limiting the flow a lot.

 

Like I said, I had to use a 5/8" hose to get enough airflow so it functioned properly.

 

I plan to do exactly what Atomic did. I have some 5/8 line coming off of the evap port on top of the hat to a 5/8" K&N filter. I'm not sure where I will mount the filter but I'll figure it out.

Looks like my garage is going to smell like corn.

 

Well I removed the brass piece from the factory vent line and it helped a lot. Still not perfect though. I was able to get 10 gallons in it before it turned off automatically. After that it clicked off every time I tried to go again.

One really weird thing I noticed is that while I was filling, the extra line that I T'd like the last picture, was spilling some gas out. Only while filling as far as I know so far. That line is just vented to atmosphere so It was somehow getting liquid all the way through it up to the filler from the tank itself. So the fluid was traveling up the line, even though my tank was between E and 1/2. The only thing modded on my tank is the pump hat, as pictured. 2 Walbros in the stock bucket, uncut.

 

Here is what I found out. The two factory "vents" do not allow air to exit, it seems they are only for intake to allow air in.

So I drilled the top of the hat and added a barbed fitting for a 1/2 vent line. It is just run up just above the filler neck right now to a filter. This fixed it completely. Only problem is when I fill, even though the breather is above the gas gap, it spills over. Probably because it rises so much faster up this vent line than the filler neck. My fix for this will be to T it into the vent line that runs into the filler neck stock.

 

Try using a smaller hose first and see if that helps.

Ive had mine spill over once or twice....race truck problems