ItsAllRigged

Im getting a pretty strong smell of gas in the cabin coming from under the hood. After I sit at idle for any amount of time (red light, etc) and then accelerate, I get a strong wiff.
On the LS3, I have removed the EVAP solenoid and looped the lines as seen below. Im wondering if this is correct or if I should just cap both these ports off instead. Maybe thats where the fuel smell is coming from?
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I have removed the miata charcoal canister and have a vent line running from the tank out and under the frame near the passenger rear axle area. Pretty sure its not this as its not a consistent smell Im getting.

Gator Bait

I used to get that smell on mine also. First noticed it on the way home from picking it up at FM (drove it home to TX from CO). I know it happened a few times after that too. I hadn't thought about it in a long time. Pretty sure it went away when I got the car tuned.

ItsAllRigged

I thought the same thing that it was in need of tuning but I just had that done on Friday and Im still getting the smell. Do you still have your evap solenoid hooked up?

tbone heller

Mine did the same thing. The fuel tank was pressurizing.

ItsAllRigged

What did you do to relieve the pressure?

Flavaquero

ice pick. Sorry lol

charchri4

Mine did the same thing as Tbones. I ran the vent line from the top of the tank through a 4 psi pressure valve to the Miata charcoal canister then to open air. I'm not sure if the valve came from the Miata or the Camaro but it was on the bench and works perfect. That canister is zip tied to the frame just under the gas tank. I can hear it hiss after driving it on a hot day but never smell gas anymore or have big time pressure in the gas tank.

ItsAllRigged

After hard driving Ive pulled over and opened the gas cap and there was no pressure or hissing. I thought I went over and beyond protecting the tank from heat by using lizard skin on both sides of the heat shields and on the underside of the tank itself. The exhaust has the banded heat wrap as well.

I'll keep this in mind as a last resort, thanks buddy.

ItsAllRigged

Well crap, I tossed all the Miata evap stuff. Thanks for the tip, guess I'll have to hunt one down.

charchri4

It could be different with an NB but on an NA if you have the ports at the top of the tank capped it's only a matter of time before it happens to you. Mine would be OK for daily driving but anything in traffic or sitting in line at an autocross even if I shut it off when not moving it would heat soak and build up pressure. I had it actually boil when I released the pressure at an autocross and it was pretty scary. With the above vent and trans cooler in the fuel return line I have not had any problems since but I still shut it off anytime I am going to sit still longer than a stop light cycle.

charchri4

Prize for the best answer

ItsAllRigged

I have a line running from the top of tank replacing the charcoal canister that dumps near the rear passenger axle.

charchri4

So nothing in the line but an open hose to the gas tank? If so that is your smell for sure. The good news is you don't have to take the cover off to run the line!

stng_96

Im going to use the small canister that was mounted in front of the shock tower on the passenger side of the engine bay. Like Jim said, I'll just through a cheap check valve in and line to that, then put the exit down toward the ground.

charchri4

It's not really a straight check valve though its a weak one. If you blow in it one direction there is no resistance and the other end takes a little push to flow. I put the push side towards the tank and near as I can tell it takes 4psi to open up and vent the tank.

Gator Bait

No clue...sorry. Bought not built.

Dave Tibbitts

I'm still using all the Miata's factory evap lines and charcoal canister connected to the LS1's factory purge valve on the intake manifold. The canister relieves the excess tank pressure and the GM factory programming is sufficient to purge the canister via the valve. Never had even a whiff of fuel scent from the engine bay.

ItsAllRigged

Thanks, this is the route I'll take.

tbone heller

That is basically the same route I went with my Ford build. After smelling a lot of gas fumes & tank pressure build-up, I discovered a stuck valve in the line to the charcoal canister as well as a melted mess of crap inside of the fuel cap.

charchri4

I thought about doing that and is one of the things on the if I was to do it over again list.

engineer

HI All,
I suffered with this issue for 2 years until I was able to find a good solution. I use the Ford EECV ECU and it has a built in purge valve strategy routine (that cannot be modified with the SCT tuning software) which I relied on to drive the Miata purge solenoid. However as the V8 miata configuration heats up the tank and gets it pressurized ever so efficiently, the ECU's standard purge routine could never fully evacuate the charcoal canister. So the car ended up with fuel smells in the cabin and from beneath the hood during long idle periods in traffic or when parking the car in the garage after a long drive. The reason for this is that if the solenoid does not activate to suck the fumes back into the engine, and the charcoal canister can not sink the fumes within the charcoal they just vent to the atmosphere.

To fix the issue I bypassed the ECU's purge canister triggers and ran a 12V programmable timer to open and close the Miatas purge valve. I used a routine of 2 secs of purging every 6 minutes. This would start and stops the solenoid as the car is running. You can hardly tell its working unless you are idling and it cuts in, the engine revs might drop by 25-50 rpm for a second and then returns to normal. It works a treat and the car never ever smells of fuel anymore.

This was a big deal for me as I drive the car daily, and on some long drives where I was stuck in traffic the fuel vapor smells would give me a headache.

So I would advise that all the standard Miata Evap systems and pipes be left in place 100%. If your ECU can handle it let it drive the Miata purge solenoid and see if that evacuates the tank vapors properly. If not running a separate timer to trigger the solenoid is a great way to fix this.

Timer was purchased from Buy Off Delay Timer Relay Online | Timers.shop

Cheers

stng_96

Very cool solution, thanks for sharing