General Smog and Chip Question...


May 25, 2001
I was wondering in general, what things need to be modified in a chip in order to help pass smog besides raising the fan on temp to around 198 or so.

Since the default A/F commanded in closed loop is 14.7:1 and no matter where you set the fuel pressure or injector constant, as long as its close, is anything really going to have an effect since the car is still going to learn to what it wants??

I've looked at the smog images on gnttype and compared them to the stock chips in a hex viewer and was actually suprised to see values changed in PE areas which wouldn't have any effect on emissions at all and other than a couple DFCO changes and such I didn't see much in the way of changes.

I burnt a chip for a friend which he drives every day and likes based off a old KB chip for stock inj and he has passed smog here in GA several years w/o a cat and that was even w/o a high coolant temp or any smog type things added.

So whats the real story to blow clean??? :)


Staff member
Jul 20, 2001
Sacramento, CA
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From your sig, it says WB O2 sensor. But I'll give you my take on O2 sensors in general. The O2 sensor helps the three-way-catalyst (TWC) function more efficient. The difference between the TWC and the Two-way-catalyst (Oxygen reduction catalyst-ORC) is that the TWC controls NOx. The O2 tries to maintan stoichiometry (14.7:1), but does it in a manner the maintains the mixture a little rich (14.5:1-14.7:1)and a little lean (14.7:1-14.9:1). When the sensor senses rich, it tries to drive the mixture lean and visa-versa. During times of rich mixture (less oxygen), the NOx section of the cat uses the absense of O2 to put the flame out and reduces NOx. During lean mixtures, the O2 is stored in the substrate (screens) of the cat and is release to complete combustion (in the cat). Perfect combustion changes HC and CO to CO2 and H2O. So oxygen is needed to complete combustion in the cat. Hope this kind of explains it.