300,000 mile NA6 Miata smog check saga

[S21FOLGORE]

I just got the car smogged recently, and it's not just another car. It's 21 years old Miata with almost 300,000 miles on it.
(My daily driver, weekend toy, grocery getter, dating vehicle.)

About the car
1992 NA6, at the moment of passing smog check it had 296,993 miles.



Things related to smog check

Original engine (head never taken off), retain stock air cleaner box set up.
Jackson Racing (carb legal) header ( due to the exhaust leak from original exhaust manifold)


Flyin Miata Hi-flow cat
Racing Beat cat back exhaust

Okay, so what do I need to do in order to pass the smog check with this high mileage vehicle ?

Let's the show begin.

1)Start from obvious things. (e.g. ; basic tune up)

change air filter



Top : new one
Bottom : old one



old one close up


change spark plugs





change spark plug wires




change oil and oil filter





2)The secret of passing ...

set the ignition timing back to stock (I normally run at 12° ).



See the line and punch mark? Punch mark is 10°, the line is 12°.



And the biggest secret is ...




Mazda OEM cat.





Compare to FM hi-flow cat that I normally use. It's twice as heavy ...


3)things may or may not help but I do anyway

Redline fuel system cleaner
Switching to Chevron premium gas (normally run on regular)

4) ... and it's been said over and over again,
completely WARM UP your car before taking test! It DOES make difference. If you have to wait at the smog check station, keep the engine running.

And the result is ...




PASS! 
(it may be a little bit hard to read. The results are
HC

15MPH 40(ppm) (Max allowed 94)
25MPH 12(ppm) (Max allowed 76)

CO
15MPH 0,02% (Max allowed 0.58%)
25MPH 0.01% (Max allowed 0.49%)

NOx
15MPH 0 ppm (Max allowed 847ppm)
25MPH 0 ppm (Max allowed 786 ppm)

[hbliam]

The numbers are so low it seems you would probably pass without any of that prep. You ever try just going in as is?

[ute]

I just run a litre of methyl Hydrate in half tank of e-10 high test


but now in Ontario they have done away with tail pipe check to many people useing this method to pass , now they just plug into the OBD port and read the ecu

[Langanobob]

but now in Ontario they have done away with tail pipe check to many people useing this method to pass , now they just plug into the OBD port and read the ecu

Same here, but I think a 21 year old Miata doesn't have an OBD port and they still do the tailpipe check on older vehicles.  We have a beater '96 RAV4 with major valve seal problems, burns a quart of oil per tank of fuel, and runs terrible due to I think a clogged catalytic converter, but it still passes the OBD smog test. 

[LowThudd]

Same here, but I think a 21 year old Miata doesn't have an OBD port and they still do the tailpipe check on older vehicles.  We have a beater '96 RAV4 with major valve seal problems, burns a quart of oil per tank of fuel, and runs terrible due to I think a clogged catalytic converter, but it still passes the OBD smog test. 

Correct, no OBD. It is an EEC IV, similar to what my 5 liter T-Bird has. That car always tested clean, even with a modified cam profile and big valve/high comp heads. I would just disconnect the MSD box so as to not confuse the smog machines tach. I used an in car timing adjuster also, so no need to wrench after/before the check.

[cokey]

Its just as easy to trick the odb as is the sniffer, think even easier... 

[S21FOLGORE]

OK, so 2 years later, and at 342, xxx miles, my NA6 is still running strong as my daily driver.
AND it’s time for smog check again.

Did all the usual thing (see my original post) and took it for a test this morning, and ...

IT PASSED !
(I’m away from home right now and can not post the scan of the print out, but it went like this.)

HC at 15MPH 34ppm (max allowed 94), at 25MPH 10 ppm (max allowed 78)
CO at 15MPH 0.06% (max allowed 0.58 ), at 25MPH 0.01% (max allowed 0.49)
NO at 15MPH 0 ppm (max allowed 847), at 25MPH 0 ppm (max allowed 786)

I’m in the pretty good mood despite the lack of enough sleeping time, have been working way too much.
At least my car and motorcycle are running great.

[Monsterlover]

That's awesome