Going to get a dyno tune in the near future. I was getting some scans while driving the car in various real world conditions. After a friend of mine ran two scans on his Z06 A8 and my Z06 M7 we noticed that the exhaust temperatures that the ECU utilizes to force a richer afr for CAT protection is a constant 50 to 60 degrees (C) higher on the right bank than the left. Both cars showed the same thing. Not sure way, but GM obviously intends it to be that way. Questions:
1. Where does that temperature measurement take place. Do the forward O2 sensors provide that info to the ECU, or is that temperature extrapolated through some sort of computer logic? I see no sensors screwed directly into the CATs.
2. Trying to figure out the best way to tune and keep the CATs from being destroyed and all the pieces blowing into the mufflers and clogging them up. I know you can gut the CATs, but I would prefer to keep them since I live in a smog check city. There are several options such as raising the CAT protection temperatures (right now there are 3 ECU threshold Celsius temperatures that trigger various afr enrichment profiles - 900, 925, and 975), lean out the afr's a little or a combo of the two. GM probably put in a very conservative tune because they want the CATs to live a long time. So there is probably some room to adjust the tune. Not sure what the best option is? Any info will be greratly appreciated

 

I am pretty sure the temps are calculated, not measured.

Tune the car with COT turned off. Then reenable it and either leave it stock or make it a little leaner than the stock setting.

Do not try to compensate for it with PE or in the MAF/VE tables.

 

Thanks.

 

I always Disable the cat -overtemp system----Even on the new DI engines----Earlier versions of EFILIVE did not address a simple COT delete on the LT1 but recently have included either a YES or NO simple tuning option-
ALSO I have been deleting COT for 12 years now--and have never had a single customer ever tell me they have had a cat failure--Cats have an approx. 10 year life anyways--
The cat overtemp is triggered by the rear 02 voltage readings--Anyone who installs LT headers and delete the rear 02's have disabled the COT whether they know it or not-

 

Thanks for the info--So in addition to checking the function of the CAT, the rear O2's send additional info to the ECU and it calculates a temperature. Then based on that calculated temperature the ECU increases the afr's when a COT temperature threshold is reached and the CAT cools back down.

 

Do you have anything showing the link between the rear O2's and a physically measured cat temperature on a GM product?

I have seen plenty of Cat Overtemp Enrichment on cars with long tubes and no rear sensors.

I have also seen AFM get disabled by disabling Cat Overtemp but have never seen AFM get disabled by deleting rear O2 sensors.

 

I guess there is no link between the two as suspected.

 

Yes On all E38 ECM's or the new E92's --If you delete the COT it will automatically disable the AFM as well---

 

As we move back to the original topic. "Do you have anything showing the link between the rear O2's and a physically measured cat temperature on a GM product?" as you stated in a previous post in this thread.

 

Ought to be pretty easy to check. Turn off the rear O2 sensors and see if the CAT temperature readings go away.