Fuel tank leaking

[oneofnone]

I am the new owner of 0247, a new build that started in 2020 and, after passing through a few hands, has now landed in my garage. Very few donor car parts on this, as 90% of the parts are brand new, like the crate LNF, etc. The car had 82 miles on it when I bought it, not really enough to sort out the bugs, and I have started to have a significant issue that I have been chasing for the last 200 miles. This car uses the aluminum gas tank. After topping off the gas tank for the first time (filled to 85% capacity), I experienced gas blowing on me from behind while driving. After a close inspection, I found the Tig weld had cracked at the seam of the tank, about 4 inches long, directly beneath the hose to the intercooler in the center top of the gas tank. After fixing the crack, I managed about 40 miles issue-free, and now I have gas leaking out around the fuel pump ring on the top of the tank. Has anyone had weld failure on their tanks before? Any idea why this might be happening? My next step is to verify the venting. Right now, the T-ed vent hose heads up under the intercooler, which seems to be different from what the direction videos show venting to the underside. Can't see what it's attached to. Wondering if you guys think I just got a bad tank and a bad O-ring, that both failed at different times (seems like a hell of a coincidence) or if there is a bigger issue at play here. Also to note. The very first time I opened the tank to fill it, there was pressure in it. Not tons, but you could hear it hiss briefly. Properly vented, should this happen?

 

[Gtstorey]

Did you remove the pump when fixing the cracked weld?

Have you inspected the vent hose for obstruction/kinking?

If the hose just goes up and doesn't come back down, it will dump the fuel if the car is upside down in an accident.

I used a rollover valve on mine for venting.

 

[Ross]

No, the gas tank shouldn't hold pressure,. Most goblins have a vent-to-atmosphere gas tank, although it is possible to keep all the gas tank emission stuff if you want or need to... then it would hold pressure.

My gas tank leaked around the gas pump, after 5 years of driving. I have the LSJ 5 bolt ring around the pump, and you probably have the LNF 8 bolt ring. I was able to stop the gas pump leak by adding a steel ring both above and below the pump flange. The extra steel ring helped spread the pressure of the 5 bolt system, and keep the green O ring sealed.

Aluminum welds don't do well with vibration, and can crack. Your goblin hasn't been driving much. Maybe just internal stress after it was welded, causing it to break early in life?

 

[oneofnone]

Did you remove the pump when fixing the cracked weld?

Have you inspected the vent hose for obstruction/kinking?

If the hose just goes up and doesn't come back down, it will dump the fuel if the car is upside down in an accident.

I used a rollover valve on mine for venting.

Is this a rollover valve? This is what the vent line runs into. It's mounted on the intake and looks like it runs into the intake. This looks to be a bit more sophisticated than just a check valve of sorts

 

[oneofnone]

I am the new owner of 0247, a new build that started in 2020 and, after passing through a few hands, has now landed in my garage. Very few donor car parts on this, as 90% of the parts are brand new, like the crate LNF, etc. The car had 82 miles on it when I bought it, not really enough to sort out the bugs, and I have started to have a significant issue that I have been chasing for the last 200 miles. This car uses the aluminum gas tank. After topping off the gas tank for the first time (filled to 85% capacity), I experienced gas blowing on me from behind while driving. After a close inspection, I found the Tig weld had cracked at the seam of the tank, about 4 inches long, directly beneath the hose to the intercooler in the center top of the gas tank. After fixing the crack, I managed about 40 miles issue-free, and now I have gas leaking out around the fuel pump ring on the top of the tank. Has anyone had weld failure on their tanks before? Any idea why this might be happening? My next step is to verify the venting. Right now, the T-ed vent hose heads up under the intercooler, which seems to be different from what the direction videos show venting to the underside. Can't see what it's attached to. Wondering if you guys think I just got a bad tank and a bad O-ring, that both failed at different times (seems like a hell of a coincidence) or if there is a bigger issue at play here. Also to note. The very first time I opened the tank to fill it, there was pressure in it. Not tons, but you could hear it hiss briefly. Properly vented, should this happen?

After following the current vent hose up under the intercooler, it appears to be plugged into this device mounted directly on the intake manifold. Any idea what this is? What would happen if I bypassed it? Wondering if this is a specific requirement for the LNF setup?

 

[duthehustle93]

That's EVAP related and you no longer use it for the goblin. I believe some people unplug it, some people leave it plugged in, but I think the consensus is to leave it unplugged. I removed mine and installed a blanking plate, and tied off the harness plug. You aren't supposed to run the fuel tank to it as that would apply engine vacuum to the tank whenever that valve actuates. This would explain your issue... are you sure the noise you heard was pressure and not vacuum? I'm honestly pretty impressed with the tank holding up... I had this issue happen once on a BMW and it sucked the entire tank into a pancake, until the car stalled because it was crushing the fuel pump.

 

[Gtstorey]

LNF with the evap solenoid unplugged will cause the car to not use long term trims on fueling. Not necessarily a bad thing, since the calculation is so basic it’s hard to say it’s useful.