AFR Commanded/ Actual
Could someone shed some light on this for me? Why or what is commanded AFR if the AFR is mainly controled by the VE table? What does changing this value do? Does this value matter in a OLSD situation? and since I amyou all to death, what is the best AFR to try to maintain? I know 14.7 is the best burn, but I remember reading that the LS1 liked low 13's for a ratio, is that just cruising around? or under load? The more I learn....the more I need to know....
Commanded AFR is your target AFR. Pretty straight forward. In open loop, it's determined by the Commanded Fuel in Open Loop table, the PE table, and any other adders that may become active. In closed loop, commanded AFR is the value represented in the stoichiometric AFR B3601 cell and again, the PE table plus any adders that may become active.
As for the rest of your questoins, the MAF and VE tables are responsible (along with the input of a few other sensors) for trying to calculate the incoming airflow. For steady state throttle and RPM's greater than the threshold of B0120, the MAF reads the incoming airflow represented by a frequency (Hz). The PCM then converts that frequency into an airflow number. For transitional throttle and speed density applications, the VE is used to calculate the airflow based on readings from the MAP, ECT, and IAT sensors along with engine RPM and some other known constants.
Once the PCM knows airflow and the desired (aka commanded) AFR, it can then determine the right injector pulse width based on what it knows about how the injectors flow.
When tuning, we reverse engineer our VE & MAF tables by reading the actual AFR and comparing it to the commanded. That's it in a nutshell.
Rules of thumb: 14.7:1 is a good AFR for cruising, 12.5~13.0:1 is a good AFR for N/A @ WOT, 11.6~12.1:1 is a good AFR for boosted/N2O @ WOT, and 14.7~15.5:1 is a good AFR for idle and light load cruise. Again, these are general rules of thumb...
Thanks againSoooo.... when if ever is it good to change the commanded AFR?
When you're tuning WOT or when you're running open loop. The stock formation in the PCM tries to maintain stoich until PE becomes active (based on PE Enable table referencing TPS% position). The factory PE table is rather rich and doesn't follow the rule of thumb I mentioned. So, when you're tuning you'll have to lean out the PE.
If you're tuning the VE in open loop, you have to adjust the commanded fuel in open loop table so that it keeps you at stoich for your operating temperature range. Just make sure you don't change PE to keep it from activating. There's some info floating around recommending that....and it's highly recommended here that you don't do that.
The VE table determines airmass, AFR is not determined nor controlled by the VE table.
B3605, B3618, B3647 set the AFR.
Changing these tables is meaningful if the VE table is dialed in (which means you reverse engineered it so that actual AFR equals commanded AFR).
You change those 3 tables (and ignition timing) to get best torque/power thru-out the RPM range (without knocking)...
e.g. people have been setting 12.5 at peak torque, and then lightly lean out to 13.0 at peak power, as Jeff said.
I have been adjusting the VE table, and it seems to be changing my AFR? Should I be changing the commanded AFR then trying to make the VE table match, meaning show all 1.00 logging BEN. I am running CO3 with SD there is a boost VE table, but no commanded AFR in boost? I was adjusting the boost VE table that seems to be changing AFR?Originally Posted by joecar
LMAO two steps forward three steps back......
You set commanded fuel and adjust VE when in SD. You're reverse engineering the VE table based on the % error between commanded and actual AFR's. Commanded fuel for the boost table should be handle by PE. If not, it should take the last row of the commanded fuel in open loop table......although, I'm not 100% familiar with the COS's. But, it should be similar. I really have to get some hands on time with those.
LMAO....by the time I know what I am doing you will be better at my OS than I am..I have to go look into this a little deeper and really look at the tables Joe mentioned. I think I am starting grasp the reverse engineering thing though. I am more "correcting" the VE table, not adjusting the AFR.
Exactly! You are correcting the VE table so that the PCM knows how much the engine really pulls in, versus the "safe" factory settings. This allows actual AFR to be close to commanded AFR in OL. This is kinda like getting the foundation level when building a new house...
2004 Pontiac GTO - Quicksilver/red/m6
1-of-344
So if I log and see that BEN is mostly 1.00 and I also notice the car is also running lean I would then need to adjust commanded AFR? Yes? and sorry, I am at work right now....still need to look at the tables more so I have a visual. New laptop up and running today though
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