I hate when this happens, but today I failed smog. My FD is stock minus the aftermarket down pipe. I have passed smog many times with the down pipe. I started using Idemitsu premix since my rebuilt engine was installed (April of this year). The last two times my car was smogged I didn't use premix and it passed with no issues. So this is where I failed, my CO (%) at 25mph was higher than max. Has anyone failed smog because of using premix or will premix cause a higher CO reading?

I'm going to try to smog my car again with no premix, but I wanted to see if anyone else had this issue, especially the California FD owners.

 

Here is a pic of my results

 

How old is the O2 sensor? and spark plugs?

Not adding the premix will help marginally, but new O2 sensor, oil and spark plugs (if old) should be enough to get you through the test.

 

Spark plugs, spark plug wires, and O2 sensor are new. They were installed April of this year. I forgot to mention a slight exhaust leak at the flange that connects to the dp and catalytic converter. Not sure it will effect the O2 sensor since the leak is after the sensor, but I could be wrong (correct me if I am). I'm going to replace the plugs just to make sure and fix the exhaust leak. Hell I'm going to put the stock pre-cat just in case. I hate smog!

 

IMHO the stock pre-cat won't help since it only does so during initial warm-up. Our '94 (now with 112K miles on it) has passed CA smog the last 6 years with a Bonez downpipe. And no EGR, no AWS. But pre-mix might cause a high enough oil content in the fuel mix to cause trouble... never used it, don't know, sorry.

Make sure your engine is up to full normal temperature for the test.

 

everything else looks ok, so I'd be surprised if you have a major issue. Your CO is above the limit but only barely in absolute terms (not like you'd expect with a failed cat or airpump issue). Your CO2% is good and so is your NOx. Exhaust leak fix + retest + no premix has a good chance to pass.