Fuel smell under boost (NB)
 

So, I've had my Rotrex on my 2000 NB for a few thousand miles and the other day I've been noticing a fuel smell in the car under boost. I've been doing some searching and seems like it may be related to my evap emissions system (charcoal canister). I can smell it with top up or top down, and was able to get it to smell just free revving on the highway (could get about 5lbs of boost out of it). If I free rev it from under the hood I don't smell anything, and don't see any obvious leaks either, so I'm guessing maybe its coming from the back of the car? Seems like it would be hard to smell something from the back while doing 80 on the highway with the top down. I could swear the smell is coming through the vents. I have a standalone, but want to keep all the emissions stuff in place for when I plug the stock ecu back in when it comes time for inspection. I also have a catch can connected to the driver side of the valve cover, which has a filter that vents to atmosphere (Track Dog setup). From what I've read, I need a check valve on the charcoal canister when boosted, which I hope to install later today. Does this sound like my issue? And does it just go between the intake manifold and the overflow can under the hood, or does it go to the actual charcoal canister in the rear of the car? Most of what I've found relates to the NA setup which has the actual can under the hood, or people saying remove it/bypass it altogether.

This is what my setup looks like. There's no line connected to the bottom of the can.

https://www.miataturbo.net/engine-pe...40/#post879617

If you are using manifold referenced fuel pressure, the fuel line pressure goes up when in boost. I would be looking for fuel leaks at high line pressure.

my fuel system is stock NB which is supposed to be a constant 60psi. Do things get screwy when you add boost? I'm starting to think second charcoal can (or whatever its called) under the hood might actually be full of fuel since my megasquirt isn't connected to any of the solenoids that are associated with it so it would never purge itself. Is that a reasonable assumption? Gotta do some research to see exactly how that evap system is supposed to work.

IIRC, Canister in front is empty. It is called a "Catch Tank". I think it is only for condensation / evaporation.

yeah, just got a chance to go out to the car and check it. no gas or even fuel smell inside. So much for that theory.

Oh, any chance it is blow-by that gets out of the no longer closed PVC system?

I thought about that which is why I mentioned the open catch can. Seems odd that it would happen all of a sudden after a few thousand miles though? Not ruling out the possibility. Also had the same catch can setup in my old NA with the same supercharger kit and a vvt motor. No fuel odors with that car, but I did eliminate the charcoal can system.

I had the same thing awhile back. If I recall it had something to do with overrun fuel cut.

try rear passenger wheel well, good chance that's where the smell may be coming from. There are several evap components in that location including canister that can get full of fuel.

I did some more checks after work. I went for a drive, and tried to do as hard of a pull as I could before pulling back into the shop, and jumped out and immediately tried sniffing around and no luck. Nothing under the hood, and nothing at the rear. Inspected the top of the tank and no evidence of leaking and no odor. I put the car on the lift and ran it in the air in 5th gear and throttled it by hand from the tb to see if I could get it to smell. I thought I would since I could smell it a little even if I free revved on the highway, building about 5lbs of boost for a split second. Nada. The breather on the catch can smells more oily not really gas. Put everything back and drove home. Pretty sure it's coming from under the hood. Even with the top down at highway speeds I can smell it, which I would think if it's coming from somewhere behind me it would never make it into the cabin. Seems to be coming from the air vents. I've read maybe injector seals, but the injectors are brand new as of a few months ago with all new seals, and it's been fine for the past few thousand miles up until this week. If it were injector seals or fuel lines, wouldn't it happen even out of boost since the fuel pressure is constant? It goes away pretty quickly once I get out of the throttle. I feel like it's got to be something simple, but this is really kicking my ass.

Has the outside air temp gone up a fair amount recently? I run a line from my manifold to my evap with a checkvalve and no solenoid. The evap keeps the gas tank from pressurizing. Next time you smell it, take the gas gap off. If the tank is pressurized, it might be causing your problem.

It's actually been a bit cooler than it has been lately. I did pop the gas cap off after the 45 min drive home and no sign of pressure or vacuum in the tank. I thought it was odd that there was no vacuum. I feel like that's a tell tale. It's currently about 2/3 full. My evap system is exactly as stock, with the solenoid going to the evap can under the hood always closed due to lack of control from megasquirt, but if something in the configuration was wrong, I would guess it would have been doing it since I put in the ms?

I really appreciate the responses and suggestions. Thanks guys!

Right, hence the question about a recent temp change. You could experiment by bypassing the solenoid and running a check valve.

I thought you were thinking it might be due to warmer temps, but it was actually cooler today. Anyhow, I'll try bypassing that solenoid and see what happens. Thanks!
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I had a similar problem that I think is solved .... though it was the reverse situation. 99 NB NA -heavy fuel smell when car was driven hard in warm/hot weather. Really noticeable after letting it sit for 10 minutes when hot then driving again. Checked all the "canisters" etc ... nothing helped. Was on a Miata group run and someone mentioned it could be a leaky injector. Fast forward to 2 weeks ago and I have my turbo setup installed and driving ... I changed injectors to FF640s as part of the upgrade. So far ... no fuel smell at all. Even driving in 90% heat and in boost, heavy stop and go traffic ... sitting at stop lights ... nothing.

Now I am hoping that was my issue and it's all good now ... time will tell for sure.

So .. don't discount a possible injector issue. Can you see around them for signs of leaks? Stains around intake?

Well, I think I found the culprit, and luckily, not injector related. Was driving this morning with top and windows up, and guess what? No odor. Windows down, and I could smell it again. Pulled the lines off the evap can under the hood and blew through the line that goes to the rear of the car and lo and behold I could smell fuel from the charcoal canister area. Pulled the purge solenoid and blew compressed air in the port going to the intake manifold and felt air coming out the other side. I assume it's supposed to be closed when unplugged? My local Advance didn't have a correct check valve so decided to plug the lines instead and see what happened. Now... No odor! Odd that I could smell it from inside the car while driving, but I guess that was it was after all. I'll hunt for a check valve or order one online, but this seems to do the trick for now. Any harm in temporarily leaving the lines capped for now? Thanks for all the suggestions, so glad this is sorted and was a relatively easy fix!

Yes, i should be closed when unplugged. I've recently replaced mine as well while chasing fuel smell and evap leak, hasn't been long enough to say it was fixed though.