Failed Emissions

[CosmoSHO]

I've got a '91 Miata, pretty much stock configuration, 173k on the clock. It failed emissions testing today--specifically HC (hydrocarbons) and NOx (oxides of nitrogen) on both the low and high speed tests.

Is there any tribal knowledge for the Miata to "clean up" the spooge easily? Am I looking at an R-squared (remove and replace) on the catalytic converter?

With other cars, I've had a few mods up my sleeve to coax a passing inspection on emissions. In fact, I've had a non-catted track car pass the emissions testing. With the Miata, my experience is limited; thanks for any input!

[Dave04]

I'm sure some of the other guys will chime in on this, but for cars in general, the first thing to look at is the o2 sensor... For a car that age, should be relatively inexpensive... (Vatozone has the Bosch universal one for ~$20)

[Titus]

If you are really close to passing, then a can of Seafoam may get you there. If it is farther off, the O2 sensor and CAT seem to be the most common problems.

[black roadster]

any codes if you jump 10 and GND?

[Sharpie]

Yeah, start with the sensor, but I bet the cat will need to be replaced too. It's easy to remove and take a look at it to see its condition.

[TheChadVIII]

Go get it inspected in Corsicana, they don't check there~

[CosmoSHO]

You guys ROCK! Thanks for the info--I'll start by pulling codes and try the O2 sensor and checking out the cats.

FWIW, it's not throwing a "check engine" light, so would the code pull indicate a bad sensor? In my SHO's, it will throw a hard light for the O2 sensor gone bad. I haven't checked the status of the cat yet, but I'll pull it. Is a universal cat okay, or is the direct fit better?

FYI--I have a welder and plasma cutter.

[HudsonHawk]

If i remember correctly the Cat is a bolt in.

[channelmaniac]

It is a bolt-in but you can have it cut out and a free-flow aftermarket one welded in it's place. They can make it fit with the bolt-in flanges from the old cat so it can still be unbolted if you want to fit a test pipe.

The free-flow will cost a little more but it's still way cheaper than OEM. Your butt-dyno will be able to tell a difference in performance with the free-flow.

RJ

[POS Racing]

Another thing that will help is to knock the timing back to 10 degrees before you get it inspected, always helped get my '92 thought the test.

How bad were your numbers???? Were you close to passing or miles away??

[CosmoSHO]

...knock the timing back to 10 degrees before you get it inspected...
How bad were your numbers???? Were you close to passing or miles away??

I'll back off the timing. Both the HC and NOx were pretty far off the mark; almost as bad as the FreakSHO with the N2O tune dialed in! What was funny was with a flip of a switch, it ran clean as a whistle without ANY cats!