Miata....catless...anyone?

Hey guys. My miata used to be catless and I would notice a constant exhaust smell permeating the cabin even while moving. Is that because I had an exhaust leak? Anyone with a catless Miata notice that before? I'm curious because there an exhaust I really like, however its only comes without a cat and from my previous experience, I'm worried about the smell permeating the cabin.

Probably an exhaust leak. I had a Miata with a test pipe and i don't think I ever really smelled the effects inside the car unless I was at a stop for a while with the windows down.

Possibly an exhaust leak but also likely because you don't have a catalytic converter filtering the exhaust. I know when my converter blew its guts out, after a long drive I smelled like a gas station after I got out. Which is exactly the reason I run a catalytic converter in my Miata. Modern converters are so efficient that they really don't restrict flow that much, and the Miata engines (except for the new ND's engine, apparently) are so resistant to bolt-on mods that you really aren't gaining anything by not having one on

I run without one. Never noticed a smell unless I sat for awhile then backed through the exhaust. With the hardtop there isnt a smell at all.

Does an OBD2 miata throw a check engine light with a test pipe?

My 1.6 runs better with a cat, but still smells like raw fuel. So I got nothing.

Top up or down? If top down, I wonder if you're not sucking in exhaust fumes from the back of the car.

Here's a Miata cat-ful:

Lof8 wrote: Does an OBD2 miata throw a check engine light with a test pipe?

I would think so, as OBD2 usually has cat performance monitoring (why you can just plug them in for emissions testing, at least in MD)

That being said, my Mustang had a catless H-pipe and I have "MIL Eliminators" for it that altered the readings from the post-cat sensors to read within expected if there were working cats...

Like these http://www.americanmuscle.com/stmilel.html

Not entirely a legal workaround...

(and I do have a catted x-pipe on the mustang now)

penultimeta wrote: Here's a Miata cat-ful:

"Yep, here's your problem. I can see it clearly. Now if I only had thumbs."

Thanks guys. The smell was bad with the top up but when i put the windows down it wasnt too bad. Does that sound like an exhaust leak?

Why not, you know, have a cat-con installed on the thing and have them check for signs of a leak at the same time?

My current system has a cat-con on it...but its a whole different system than before.

Japspec wrote: Thanks guys. The smell was bad with the top up but when i put the windows down it wasnt too bad. Does that sound like an exhaust leak?

Yes, I've driven a bunch of catless Miatas and never noticed an exhaust smell in the cockpit.

Is the upper shifter gasket intact?

Could it be the charcoal canister and evap system?

Gasoline is constantly giving off vapor, and that vapor smells. Evap systems are supposed to suck up the extra vapors and store them in the charcoal canister or burn them in the engine.

Sometimes, people will pull their Evap systems for 'because racecar', and then you smell like gas all the time.

Even if not the EVAP, could be a leak in the fuel tank. Gas tank is just under the rear shelf behind the passengers, right? If not sealed fully you could have quite the smell inside I imagine.

Thanks everyone. I think it was most likely a leak and nothing to do with the evap system. Currently I have the catted roadstersport system, and I don't smell anything at all. Under hard acceleration, I will sometimes smell it, but thats about it.

Mine is catless and I get an exhaust smell, some at rest but more when moving. Hardtop, windows up or down. AC on. All new shifter hardware in the last year.

I don't hear any leaks but next time I can get it in the air I plan to check around.

MattGent wrote: Mine is catless and I get an exhaust smell, some at rest but more when moving. Hardtop, windows up or down. AC on. All new shifter hardware in the last year. I don't hear any leaks but next time I can get it in the air I plan to check around.

Interesting. Seems to me like it must be hit or miss with the smell. Almost a 50/50 split between smelling it during moving vs. sitting.

Well I decided to buy the exhaust I wanted, so when it gets here and I get it installed I guess I'll see what happens. Fingers crossed!

Mine is from Mandrel Bending Solutions (MBS). Its loud, but not raspy, and relatively deep for a Miata. I like it for a track car - not for DD.

Car is on interim DD while I shop for a new one, I wear ear plugs on the highway.

NickD wrote: Possibly an exhaust leak but also likely because you don't have a catalytic converter filtering the exhaust. I know when my converter blew its guts out, after a long drive I smelled like a gas station after I got out. Which is exactly the reason I run a catalytic converter in my Miata. Modern converters are so efficient that they really don't restrict flow that much, and the Miata engines (except for the new ND's engine, apparently) are so resistant to bolt-on mods that you really aren't gaining anything by not having one on

In our dyno experience, the ND is more resistant to bolt-on mods than any other Miata. But that doesn't sell parts, so you are seeing aggressive marketing to the contrary

There's no reason to run a Miata without a cat, and they do smell without one. An OBD-II car will definitely throw a warning if you run with a test pipe, it is monitoring cat function constantly.