fuel smell odor when under boost
 

Someone point me in the right thread if this has been discussed before because I could not find it.

At full boost (11psi) there is a slight air vibration sound from under the hood (like if you would blow on a reed), and there will be a strong fuel smell. I can drive the car all day and all is normal, until it hits 11psi.
I'll stop, check around the motor and see and smell no fuel. All this started after I removed the stainless header to repair some cracks (damn BEGi S4 manifold) and have it ceramic coated.
So today I pulled the fuel rail and injectors thinking an o-ring has torn, but all look ok. I haven't put it back together yet so let me know what I should check next or if yall need pics.

Stock fuel rail, 550cc injectors been in for 2 years.

You may be missing the check valve between the intake manifold and the charcoal canister to prevent boost entering the latter.

Canister deleted. But thanks for the quick reply!

Do you have a wideband?

Yep.

Figured this is irrelevant but also have a slight crack again in the exhaust manifold. :facepalm:

Any other ideas before I pick up my tools for the night?

I'm not sure, but this might have something to do with it.

What are you doing for excess crankcase pressure? I just have a breather filter on my VC port, and I think the vapors coming out of that in boost was giving me slight oil/gas smell under the hood when under boost. I mean I never really looked into it, but that was my first guess as to what was causing it.

A leakdown test would really be necessary to better understand what's going on here.

Hmm, depending on how it's setup, maybe your IM is pressurizing the fuel tank, pushing vapor out the vent line!

Had a similar case the other day. Car had all new fuel lines, aftermarket FPR, etc. It would smell fuel inside the cabin past 8psi. The problem was that one of the fittings (which was near the (now deleted) A/C bulkhead was not tight enough, so whenever the boost went up, so did the fuel pressure and there was a very small leak. It was ok idling and on low loads.

If that's my case, then when I put it all back together with fresh fuel lines and clamps, then all should be golden.


When I removed the canister, I just looped the fuel vent line straight to the hose that runs into the front subframe. The intake manifold port is capped off. Is this wrong? This mod was done way before I noticed this issue though.

Cheap inline filter with some clear hose installed a year ago, tested and still clean.

So I put it all back together with fresh fuel lines, clamps and o-rings. No noise or fuel smell now, yay.

Spent the rest of the night fighting with the bolts and studs on the S4 manifold. Found 2 long cracks near the welds and a few pin holes. Fck! I just had this thing repaired and ceramic coated.
https://www.miataturbo.net/attachmen...ine=1328377859

Next time you "fix" the manifold have who ever does your welding put in a support to keep weight off the joints and keep vibration to a min. This will help if not stop all the cracking.

Are you familiar with stainless? It flexes when heated = can not weld supports.

There is a pivot bracket mounted to the downpipe keeping some weight off.