I am trying to tune my AFPR with the LTerms and Sterms on my datamaster. I cant seem to get them to get an accurate reading. At one point the Lterms are at 122/124 and at the same point my Sterms are at 130/228! This is at about 10% throttle. Usually the Sterms are right at 128 or just a bit under but the Lterms are all over the place. Can someone tell me how to interpret this data?

 

Joe, that 228 is likely a glitch. the Lterms max out a 160 so anything over that is bad data...id assume the Sterms max out at 160 too. and the 10% throttle doent mean jack. you need to get the Lterms corrisponding with certain cells.

 

Brad, what do you mean by cells? Is there anything else I should be looking at to extract more meaning from the Lterms?

BTW how is the RR install coming?

 

There are 16 different "cells" used to store closed loop long term fuel corrections (and a couple more for open loop operation - 18, and rundown loads - 17). The cells are defined by various levels of RPM and MAP. Cell 01 would be low RPM, low MAP; Cell 15 would be high RPM, high MAP. (The PCM uses MAP as an indication of engine load).

Go to my ScanMaster writeup, and go down to the Air/Fuel Management section in the middle. Explains how it all works. You might want to go through the entire writeup, to understand the meaning of a lot of the data that TTS DataMaster is capable of providing.

USING SCANNER DATA

 

Fred- Thats a great write up, thankyou very much.

I have one more question that isnt so much related to fuel but I figure someone here could give me a quick answer without starting a whole new thread. On the Datamaster it does not show my car going into open loop at WOT? Should I be worried about something?

 

Its just a matter of "words".... GM only calls the cold start conditon "open loop". They call the WOT condition "power enrichment". In both cases the O2 sensors are dropped out of the control loop. But what DataMaster indicates is not that it is actually operating in "closed loop", but that all the conditions required for "closed loop enabled" are met. It doesn't mean that the O2 sensors are still in the control loop at WOT, only that the system has met all the requirements to allow closed loop to operate when it is supposed to - coolant above the minimum required temp, O2 sensors heated and active, elapsed timer since startup timed out.