Tricking the computer on cat temp?

Why would you want to trick the ECU to run the cat cooler?

 

You just temporarily trick it into thinking the coolant is warmer to get the engine from constantly running and burning more fuel.

rather complex to save fuel

 

The stock program wants a certain temperature for clean burning.

Spoofing it lets you burn less fuel overall, but what you do burn is going to generate substantially more pollution.

 

If CO2 Is pollution and spoofing the sensor saves 20% fuel on a short trip (which is very possible) are you really creating more “pollution”?
Or is it a mixed bag like everything?

 

I've never had a car instrumented well enough to answer that question. I write it off to the idea that the driver wants to save fuel, and the manufacturer is required to hit certain emissions targets. Those two goals aren't necessarily in harmony.

Just to point it out, there is another way. Set the car up with a block heater. Then you don't need to burn gas to get the heat that allows you to burn cleanly. Economy improved and emissions reduced in one move. Also it's practice for the day you get a PHEV.

 

Related to ethicality and environmental effects of this:
Different greenhouse gasses have different effect on atmosphere but the effects can be calculated/evaluated. Reducing the car's fuel usage (CO2 emissions) by changing the way the engine runs, in a way that would increase other emissions (to acceptable level), would actually decrease effect on global level. But it would also make it worse in local emissions.

If this is done in an environment where local emissions are not that important, like area with lots of forests (good local air quality) and not many people, this would be a good thing. But in a big city where the bad air just stays that would be very bad thing.

Theoretically manufacturer could create a map and change how emissions a dealt with depending on a location. So basically changing balance between fuel consumption (CO2 emissions) and local harmful emissions.

Feasibility of any mod like this:
It's not going to be that easy. Colder catalytic converter will work less efficient (hence the increased emissions) and that would create the code for catalytic bad converter P0420. Colder running catalytic converter will start to get blocked more easily and then you will use more fuel. And many other possible problems.