Note that the CO2 reading on my car was at or over 15 percent. The 560 numbers were about 14.5 percent, and I attribute this to to the substitution of ethanol for MTBE which has decreased the average carbon/hydrogen ratio for the fuel.

The reason you have low CO2 is because you have high CO. I doubt if there is a problem with your cats. Your mixture is too rich!!! Look at the numbers for the 560, and note that CO2 is 14.6% at 25 MPH and CO is zero. If we were to richen the mixture to produce 1.0 percent CO the CO2 would drop to about 13.5 percent. The basic formula is %CO2 + %CO = 14.6. Whether the sum is 14.6 or 15.3 will vary with the carbon/hydrogen ratio of the fuel blend.

The reason you have high CO is because your mixture is too rich, and without supplemental air injection there is not enough O2 left over from combustion to oxidize the high CO that results from a richer than stoichiometric ratio. O2 is measured during the test and the reason yours read zero is because it IS zero. A rich mixture will consume virturally all the O2 during combustion and increase CO. With so little O2 in the exhaust there is not enough to oxidize the excess CO and HC.

As stated, on most modern cars that have supplemental air injection, it is only active during warmup, but that's not an issue with our cars because they don't have air injection.

From what you mechanic is saying I don't think he understands how engine out emissions change with air-fuel ratio. You need to find someone knowledgeable of the KE system and have them troubleshoot and correct the rich mixture problem that your have. Once corrected your emissions should be okay.

CO is linearly proportional to air-fuel ratio. At the typical stoichiometric ratio of 14.7:1 CO is a fraction of a percent. At 12.5:1 CO is about 6 percent. Modern emission control systems maintain the air fuel ratio very precisely at stoichiometric (except at WOT) by measuring O2 content.

At stoichiometric, 02 is close to zero, but rises rapidly with leaner mixtures. The high sensitivity of O2 sensors, their rapid response, and the sudden rise is voltage with no O2 content is what allows modern electronic engine contols to maintain an average 14:7 air-fuel ratio and control emissions with three way converters. The system runs (very slightly) rich-lean-rich-lean and crosses over the stoichiometic point several times per second as indicated by the rise or fall of O2 sensor output voltage between 0.2V and 0.8V If this control is lost the mixture usually becomes to rich and you bust emssions.

You can observe the actual waveform of the O2 sensor output with a scope, and watch it jump back and forth. If you measure it with a DC voltmeter, it should be about .45V, which represents the average voltage over the cycle.

At about 500C the O2 sensor output will "jump" at less than 0.1 deviation from the stoichiometric ratio.

Duke