Hello, random/ annoying thing happened. Was driving the car for about 45min, filled it up before I went home. Got home and put premix in, I usually leave the funnel and measuring container propped in the fill hole for about 15min to let it all drain in there. Came back out about 15min later and gas is pouring out of the fill hole? I’ve owned the car for about 5 years now, and it’s never done that. I’m assuming it’s a vent somewhere? But not sure where to start. I still have chacoal canister nothing has been removed. The white 2 way valves on the sending unit are new. Any ideas?

Edit: drove it again today for about 45min, I didn’t remove the gas cap or anything, but towards the end of the drive felt like it was running lean above 4k rpm because it was breaking up. Just went out to see if I could see anything and it looked like there was dried gas going down the side of the car coming from the gas door.

 

They're one way, if they were reversed and the car was heat soaking or out in the sun, the fuel might find the path of least resistance. There's a ~10mm / 3/8" breather hose between the upper fill neck and the tank, that might provide that escape route if the fuel level was high enough.

Beyond that, more remote possibilities, the two breathers on top of the tank....never heard of one failing.......worst ones I've seen, had only a liitle surface rust internally. The butterfly valve at the bottom of the fill neck (tank end, behind the inner guard) is probably the last option to inspect.

 

it does seem to only happen once the car is warm. I made sure to keep the arrows on the valves pointing in the same direction when I put new ones in. I will definitely give all of those a look thank you! Idk if it makes a difference, I didn’t clarify in my first post, but all emissions items under the hood are gone. From the engine bay back however is the same. I have the charcoal canister to atmosphere. I also read on here there’s a slim chance is fuel cap related so I ordered a new one of those just in case.

 

If all emissions items are gone... what did you do with the evaporative purge solenoid? That's what mixes gasoline vapor with intake air, especially when hot.

 

the canister hardline is just open to atmosphere under the hood

 

There is another small hose that goes with the larger fill hose to the tank. If that is clogged, what your describing could happen.

 

I did see that when I looked real quick, about 3/8”? Maybe I’ll pop that off tonight and see if there’s anything in there

 

By way of explanation, that small tube vents the tank at the top. The filler tube is lower and may be totally submerged in fuel when the tank is almost full. So that's why a clog in the vent tube could cause this. A clog there could also cause fuel to spit back while filling the tank.

 

Muffler heat shield(s) still in place?

 

I took the vent tube off and blew it out with air, nothing came out and seemed very patent. It actually fills up fine and stops when it’s supposed to, it happened after it was setting after drive.

they are. Do you think it could be heat related?

the butterfly valve is also functioning appropriately, or at least it seems that way when I looked at it. Pic is upside down for some reason but it’s closed.

 

Well gas could be expanding in the tank due to heat. But it is hard to imagine how much that would contribute. I suspect a leaky gas cap and just enough gas somehow slopping out to leave a stain. it would not take that much. The stock cap does have a venting function.

Do you recall any release of pressure (psssst) when you take the cap off?

I wonder if the FPR if closed due to loss of vacuum, or sticking shut, would that push the pressure all the way back to the tank?

Any sense that you are running rich?

Do you have an afr gauge?

 

Definitely has release pressure. Have a new gas cap coming in today just incase that’s all it is. The one point where I saw it coming out the first time, gas had come up and filled the fill spout to the brim and was overflowing and then went back down after a few seconds.

I was also contemplating the fpr. It is a brand new fpr though. I have all new radium fuel rails, fuel lines, fpr etc…routed feed-primary-secondary-fpr-return.

maybe running rich on start up and warm up? New motor still in break in period. I suspect running lean when car is warm. Anything over 190 deg h2o temp it starts breaking up around 4k rpm, didn’t have my laptop to run a log to differentiate between the tune and fuel issues. I had a thought maybe there’s a vacuum/vent discrepancy in the tank causing it not to send fuel.

I do have an afr garage. I was looking at fuel pressure when it happened (which was fine) and didn’t pay attention to afr. I’ll try to drive it today and fill in some information gaps.

also saw there are two fuel vent caps on the tank, what are the chances those went bad?? Relatively low mile car. 50-60k miles. Put vacuum to the charcoal canister line, and it didn’t hold vacuum at all which I’m assuming is the way it should be

 

I have seen gas leaking out from a cap on a car that was parked perpendicular to a slope, with the filler neck pointing downhill. . Was your car on flat ground?

 

In hot weather I sometimes smell gas near the fuel cap, so if vapor can leak out, so could fuel if the tank was full and parked like Redbul said.

 

Butterfly looks ok, tabs still in place, so shouldn't let fuel surge up the neck in cornering.

As said, very unlikely to stuff up, the only thing I've seen is light rust on the perforated steel bit inside on an otherwise rust free tank. If the tank has been left empty for long periods with lots of condensation cycles - maybe a greater chance of malfunction.

The rubber hose loop leading from the breathers if it was somehow pinched between the car body and the tank might cause issues, if you've dropped the tank and somehow got it on top of a rub strip, but that's clutching at straws really. No mud daubers up that way?

 

What, is a "mud dauber".

 

yea it was in my garage, ground is level. I did put a new gas cap on yesterday, haven’t had a chance to drive it

I was thinking the same lolol

I have a brushless pump, which from my understand runs cooler than your normal brushed pump. Could the heat from that be causing expansion too fast? I don’t know of too much more that could cause it. Unless the vent tube is clogged in the actual fill neck piece, I may take it off again and blow some air in the fill neck connection.

 

That's a type of wasp that builds egg pods by dabbing mud it creates inside a small tube like an AC condensate drain or make a mud tube on a vertical surface to lay its eggs.

 

Ah I know what you’re talking about, never knew the name of them though lol from what I can see no signs of insects in all observable areas

 

It takes something like exhaust heat or continual hot air flowing under the car while driving in hot weather to heat-soak the fuel tank enough to cause enough fuel volume increase to cause overflow. It can even happen just due to a large ambient-temperature increase after filling. And usually, fuel coming from an underground tank is pretty cool, like 55F, sometimes making the same issue happen as it warms up to ambient.

And if you are in the habit of "topping-up," i.e., filling to the brim with small fuel fill pulses at the end, that will make the issue more likely.

 

im running a 20b which usually runs hotter than the 13b. I don’t have an undertray currently, so maybe more heat being let out that way heat soaking the gas tank? Might be a long shot, just trying to look at it from all angles 😅 I do not top it off though. Soon as the pump clicks off the first time, I’m done.

 

If you exhaust is somehow restricted, it could heat up more than normal.

See if your turbo is glowing after a cruise.

 

The turbo is not glowing after a cruise, I have to flip a breaker under the hood due to a parasitic draw so I look at it every time lol I don’t think my exhaust is restrictive. Not cat on it and the muffler seems to be operating as it should. I’ll have time to drive it around Monday, I’ll see if the new gas cap makes any diffference. I have low confidence in it helping but weirder things have happened

 

What is your fuel pump setup like? A coworker built a fuel pump test rig which was basically an entire fuel system without an engine, and just running a single fuel pump can heat the fuel more than you might expect. The electric motors inside most fuel pumps are generating enough heat that they can be damaged if they run dry without fuel to cool them. If you've got two or three beefy fuel pumps running at full blast to support big 20B power levels, the fuel might be expanding more than you realize even without the engine running.

 

Yes, the little buggers love finding holes and filling them. Not so much here, but further west, they're rife and will fill aircraft tank vent tubes and pitots overnight if given an opportunity.

In the twilight zone, I assume you've got an early fuel tank with the little expansion tank on top. I couldn't imagine any possible way it could go wrong, very lightly pressurising the line leading from the first check valve to see if air gets to the line opposite, likewise the catch tank under the TB might be worth a shake to see if it's maybe blocked with charcoal bits. The charcoal canister itself has a rubber vent, but don't quite understand how that works.

Used to find the muffler side of the tank gets warmer than the rest when jacking it up after a session, but it's surprising how hot the tank gets generally - recirculating fuel in the engine bay (which might be an argument for a dead head fuel system), do you have a muffler heat shield in place?

Edit: Oops, same point raised above.