Quote: Originally Posted by
Simon.Starkie 
I have a couple of questions for the SRT engineers:
1. How exactly does the PCM calculate EGT's? (what are the input parameters).
2. What does the PCM use the calculated EGT's for? (is it just a byproduct calculation or does it actually influence the PCM to change other variables like boost, ignition advance timing, injector pulse widths, fuel trims).
Obviously, noone in the right mind would tune a car based solely on calculated EGT's. But those of us with OBD-II scan gauges are aware of the calculated EGT readout and would like to know more about it. Unfortunately, the PCM is a black box to everyone outside of DCX, hence the question to the SRT engineers.
Thanks!
I'm not saying this is the best way to tune, but back in the day when wideband sensors were uber expensive, they would have a test motor/car on a dyno and run through simulations of running rich and lean under certain instances. Both EGT's and and AFR's were logged. There is a basic correlation that is compiled from this data and the engineers are able to develop a basic table or two that will run safely without the use of a wideband.
One example of this is the old MBC. Most pre 2000 turbo cars can easily be fitted with a MBC for a power increase. If the boost was turned up too much then the car would go boom. No 'safety-net'. The NGC controller does cross checks and even though we are bleeding pressure off so the pcm isn't seeing the full boost amount, if we stray too far off (usually 3-4psi) it will pull timing like crazy and adding more fuel because the EGT's have gone up and no longer correlate with the tables. Most then add W/I to counter the increased egt's to take advantage of the MBC.... does this make a little more sense?
$.02
