The PCM's thought on COT?

[Redline Motorsports]

I don't know why I am thinking about this now but...............if COT is to protect the cats from overheating and the PCM commands a rich mixture to protect them how does it know that it needs a richer mixture? Also the temperature values that are stated in B0701-; how does the PCM determine the theoretical temperatures and compare them to make the determination to cool the cats?

Finally, how much of a a temperature variance makes a difference in playing with the cats?

Howard

[SSpdDmon]

[dfe1]

From what I can see, COT is based on predictive values using rpm, load and time. When I first started tuning LS1s, I noticed commanded air/fuel always went to 11.7:1 at about 4000-4500 rpm. This was on the dyno and it didn't matter whether the engine had been running for 15-20 minutes or had just been started, warmed for a few minutes and run.

I don't get the over-temp deal because excess fuel is what kills converters-- the more fuel in the exhaust, the higher the converter core temperature. Too much fuel and you've got your own private barbeque.

[joecar]

When you have a non-firing coil/plug or two, watch the coverter on that side glow red hot...!!!

[dfe1]

When you have a non-firing coil/plug or two, watch the coverter on that side glow red hot...!!!

That's exactly what happens when anything causes excess fuel to enter the exhaust system. Raw fuel is really the issue because the hydrocarbon content is so high. To a degree, rich mixtures (the operative word is mixtures) don't hurt anything if they don't last too long, and if all the fuel has been involved in the combustion process. But when raw fuel hits a converter substrate, it's literally like throwing gasoline on a fire.