squishball

I thought I throw this question out to the auto diagnosticians, who have been very helpful to me with my ar problems. My 1990 Miata (aftermarket supercharger, etc., see signature) just failed CA's more stringent Smog Test (with simulated road test). My NO measured 2506 ppm @ 15 mph and 1823 ppm @ 25 mph. The max allowed to pass is 847 & 786, respectively. My car has been designated a Gross Polluter, having even exceeded its limits 2070 & 1870, respectively. CO (%) was 0% & passed; HC was low & passed. Where should I look first? The car has only a PCV, Cat, Fuel Evap container, and O2 sensor. Tested my O2 sensor, and it may be defective. Thanks for your help

tremor12

Can you lean it way out? Depending on your management, you may have a lot of options, or a few... (If I had to pass emissions with my Link, there are a number of ways to pass... the car barely runs when you're there, but just reload a real program after...)

moto-one

What just taking it (SC) off for the test, or was it a CARB approved system?

xtreetoes

See the thread started by Dave.b below. Nice explanation about NOx. You don't want to lean out the mixture will make NOx worse. If the car does not have an EGR valve you will probably need a new cat converter.

skidmark

can you run with stock fueling chip and belt removed off blower?

skidmark

also wonder if running some 100 octane unleaded may help lower combustion chamber temps

want

<ul><li><a href="http://www.gatewaycleanair.com/mechanic/air4_4/dirtymaf.htm">http://www.gatewaycleanair.com/mechanic/air4_4/dirtymaf.htm</a</li></ul>

exactoroland

afterall, all that black stuff they belch is exempt from emission controls. Just joking. All the best in getting your Miata to pass. If it passed before, I'm sure you'll get it to pass again.

squishball

Miata only has 34,200 miles

It was smog tested with mixture of 1/3 100 octane race gas &amp; 2/3 pump 91

Stock ECU and stock program, mechanical MAF (barn door), and 3rd party J &amp; S knock sensor (retards timing on an individual cylinder basis).

Stock timing is 10 BTC, but I have it now at 12 BTC.

Supercharger is CA Air Resources Board legal. It only runs under sudden acceleration. So, in theory the supercharger does not produce boost when the car is idling or crusing at highway speeds (which is essentially the conditions the CA Smog Test tries to replicate by running the car in gear at 1500 and 2500 rpm).

Supercharger is controlled by a vacuum bypass system, remains closed when power is needed and opens up with vacuum greater than 5" of mercury (open = supercharger is bypassed). I can manually bypass the supercharger by locking the vacuum bypass valve in the open position (which I didn't do when the car was smog tested).

Fuel Management is controlled by an aftermarket pneumatic fuel pressure regulator. In non-boost conditions, stock Miata regulator controls the fuel rail pressure (5 - 36 psi). On boost, the aftermarket regulator takes over and raises presure 7 psi for every 1 psi of boost to a maximum of 75 psi.

Last note: This is the first time Miata was tested for NO emissions. All previous CA smog tests looked only at HC &amp; CO emissions.

Thanks again