will adding ethanol fix my emissions?

I thought dry-gas would help me once.... ruined my numbers..... my.02

It's a 92 Cadillac STS, so i don't think it has OBD yet. It does have various monitoring systems, and is able to display O2 and MAP sensor readings on the display in diagnostic mode.

The trouble is, my CO readings got closer to the limit with every emissions test over the years. Ahead of the last test, i thought i'd rather install a new catalyst just to be sure, but it didn't give me a good margin, and didn't even change the trend. I still passed the test, but the CO was one step short of failing.

Here's the CO readings during idle 650 rpm:

this year (with new cat): 0.45

max. CO: 0.50

Everything should be tuned up well. I checked ignition timing to be within specifications, spark plugs aren't that old either. One trouble i do know of is excessive heat while idling, always close to or displaying a "enginge hot" warning message. The reason for that is known (cooling system issues), i just wonder if a hot engine can have bad emissions for some reason. Also i wonder, can higher idling rpm have a bad effect on the CO-value? Are lower rpm always causing lower CO?

Complicated issue. ethanol results in less of some emissions, more of others. However, CO is one that it indeed improves.

forgot to tell: O2 sensors were replaced with the catalyst, too, all new OEM parts.

How about high octane gas? I didn't use it since i always noticed less mileage with premium fuels. Isn't it then higher emissions for the same rpm because more fuel is burned?

What effect if any could exhaust system pressure/reduced flow have. There was a different muffler installed before the test and there might also be some crimping of pipes that restricts the flow.

About catalysts: can't someone that fails the smog test just install TWO catalysts in his vehicle and it will literally _knock_ the values down? I read that GM was using auxiliary catalysts in corvette engines to keep them within emission limits in California.

In fact, it does. OBD started in the mid-'80s, and all '92 US-market cars have it, including your Cadillac.

OK...find and fix the problem!

Don't replace parts "just to be sure". Replace parts that are indicated as faulty by means of proper diagnosis. This "add alcohol to cheat pass the test" idea is schlock. Fix the damn car! If you lack the knowledge and tools to do it yourself -- a spark plug wrench is no longer sufficient -- pay to have it done.

DS

The engine had been run for 10-20 minutes before the test, it's true though that ahead of previous tests it was cranked more intensively.

Suppose there was a screw with the rpm during the testing. What would the CO % be at a higher-than-normal idling rpm?

At 2800rpm, the CO value goes down, as there is also a lower max value for this speed. The difference is also the EGR valve allowing more exhaust to recirculate at higher rpm.

...IF the engine is running properly. If it is not, then the catalyst won't compensate.

Maybe the catalyst is supposed not to compensate any much during idle - because of the lower temperatures. The CO limits are higher for idle than for high rpm, i wonder if this could be the reason.

There are other reasons too. The ratio of cool surface area (quenching area) to the volume of fuel air mixture is far higher under idle, so the surface walls quench the combustion more effectively. More of the charge is cooled and combusts incompletely. The amount of heat energy generated in each cycle is proportional to the volume (actually weight) of charge, but the cooling surface area is independent of charge volume/weight.