Slight fuel leak, very pressurized tank

I have a slight fuel leak I haven't had the chance to identify. If the car is laid up for a few weeks, there will be a small puddle under it. Doesn't happen all the time, seems intermittent. I'm currently at a quarter tank. I just brought the car down from its upper position on the lift because our weather is finally nice, and went to fill up the tank today. After a several minute warm-up and several mile drive to the gas station, I took off the cap and there was an unexpectedly loud whoosh of air outward from the filler neck.

I'm suspecting the pressurized tank, if overpressurized, may be contributing to the leak. What do I look for (besides inspecting the tank for holes/cracks) in diagnosing it? Thanks.

 

Thanks, Ernie! I've read your posts, including the beautifully detailed engine-out service. You are a credit to this site!

 

Yeah, fuel leaks are scary, especially having seen all those pictures of Ferraris on fire.

In case anyone finds this thread looking for answers, here's Ernie's excellent thread addressing the anti-rollover valve:

http://www.ferrarichat.com/forum/technical-q/453019-348-anti-rollover-valve-anti-tilt-valve-replacement.html

 

Partial update:

I read not only Ernie's anti-rollover valve thread, but also his imploding gas tank thread. I feel like I'm mildly educated in Ferrari 348 tank fume management.

I don't have a lot of time to fully investigate this pressurized tank issue of mine (I'm obsessing over a slow restoration of an FJ40), but I did pop the engine lid and had a look. I pulled the line off the bottom of the anti-rollover valve, and heard a couple tinkles of what sounded like pebbles falling out of the hose. Are you thinking what I'm thinking?

I connected a separate clear hose to the nipple as a straw, and was able to blow through it with some pressure and get a quiet cazoo noise. I wonder if this valve was plugged? Surely, the amount of pressure I noticed at last fill-up should have activated the cazoo. Should you be able to blow through the bottom (tank side) of the valve easily?

 

OK, I have an update and a solution for this thread. I continued having issues with tank pressurization as the fuel in the tank got hot from driving. I had to leave the fuel cap loose to relieve the pressure until I came up with a permanent solution.

A replacement rollover valve is unavailable. I cruised eBay, and found one from Chrysler that also fits the DeLorean. Only $25. Look to be about the right size. I ordered it, and it came with a bunch of DeLorean literature packed with it. Kind of funny.

I trimmed it up, but looking back, I probably should've left one of the existing plastic mounting tabs as it would've likely fit on the existing 6mm mounting stud. Anyway, I used a bit of rubber to shim it up, and used the original mounting clamp. Because the nipples are in opposite directions, I had to use a longer replacement hose going from the valve to the carbon canister. All I had on hand was that grey poly tubing for my motorcycles. I'll get the correct cloth-braided fuel hose tomorrow. I was able to do all of this from above, I did not remove the wheel and liner, though it would've provided better or easier access.

Anyway, it's all buttoned up, went for a good drive, and there was no whoosh from the gas tank when I unscrewed the gas cap, and no fuel leaks. Fingers crossed. Soooo, does this make me a stooge?
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Thank! Part number on eBay is 4002012, using the search modifier "rollover valve." Looking that up, the most common hits are Jeep CJ, Chrysler, and of course DeLorean. If you're shopping directly from the DeLorean parts site (DMC) the number is 101402.

This is just a ball valve with the correct sized nipples and almost correct dimensions to fit in the original clamp ( after some Dremel work). Summit racing also sells a fuel check valve that would probably work if you attached a couple of adapter barbs, and zip tied it right side up. Would probably work fine, though look less correct.

 

The difference between the two valves, is that a take some force to blow through the lower hose on the original valve, and then I get that faint kazoo. With some attempts, it remains completely obstructed. I think that's how my tank gets pressurized. This all happens even though you can hear the ball rattling around inside.

The new DeLorean valve flows freely in and out through both hoses, without resistance, unless the valve is tipped sideways. No obstruction or kazoo. I did some more Internet searching, and found this other valve from an old diesel Mercedes, which might also work:

https://mercedessource.com/store/search?keys=DSL-COMFTVV