im sitting here looking at the graph rpm % change. and some of the numbers are .4 and 2.3. what are the a/f ratios using those 2 numbers. for exapmle 2.3 % change is that 12.5to1 or 11.0to1. i just dont know what the percentage numbers are a percentage of is it fuel, air or bought.

please help me understand this.

 

I think it adjusts the fuel at those points...so if you go +2.3% it will add that much more fuel at that rpm point

 

i believe the target AFR is 12.8:1(i could be wrong though) in WOT so that chart just increases or decreased the AFR probably by cutting or adding fuel depending on the % change in the chart.

EDIT: ok i just did some checking and it bases the chart on the closed loop AFR of 14.7:1 and increased/decreases it by the % change in the PE tables at WOT.

 

if im changing a percent of a number what number am i starting at.

and how do you turn the percent # to a accual a/f ratio number. what equation do you use. for exaple 3.1 percent change= 12.8. how do you get that.

sorry if im not making myself clear.

 

you start with 14.7:1 and multiply that by (1+%change). of course if your BLMs are not perfect then that will affect the ACTUAL afr. only a wideband will tell you what the true afr is.

 

so it would be 14.7 x 2.3%(.023) =14.36to1 a/f ratio. correct, it not please help.

from 4400 rpms up they are set at 2.3 % change. and i want to know what a/f ratio that is.

 

here look at this site... go to the bottom of the page. what you did looks correct to me but i dont think thats how it works exactly.

 

so basically what youd do is take the 14.7:1 closed loop AFR.. divide that by (1+%change in coolant temp)... then divide that by (1+%change in RPM).

so looking at the charts i got an AFR of 11.7:1 at about 200*F and 4800 RPM.

 

you are probably geting irratated with me but could you write out the equation the way you worked it.

i tried it buy what you said above but i dont no what happened.

thanks for the help.

 

you have to look at the PE tables in tunercat or LT1edit first to get the %change in AFR.

you guess the temp at which the car will be opporating.. probably around 180-200 which is 15.6% fuel increase. since this is PE or power enrichment mode... you want a richer value than 14.7:1 so you simply take 14.7/(1.156) to get 12.7:1 AFR. but you arent done yet b/c this was just for the coolant temp.. still need to adjust for the RPMs. so you go to you PE vs RPM chart and with the 12.7:1 AFR you will divide that by a factor of (1+%change vs RPM). 5200 RPM is an increase in fuel by a factor of 9.8%.. so thats 12.7/(1.098)=11.6:1 AFR. that is really quite rich but that is what GM called for... ideal is around 12.5:1-12.8:1 but youll need a wideband O2 to do it right. like i said the BLMs also play a role in this. the AFR is calculated for a perfect 128 BLM so if the cell you are in before cell 15(WOT) is 110 then i believe the AFR is also changed by a factor of (128/110)~1.16. so that would be 11.6(1.16)=10:1 AFR! now i am only guessing the BLM factor so dont take my word on that hope that helps.

 

thanks alot i got it figured out. you wer a big help. accualy my only help thanks. because i was really but now im

 

Keep in mind that these are the values that the PCM is trying to aim for. They do not indicate ACTUAL AFR at WOT. To tune WOT correctly you need some type of performance meter and a wideband O2 sensor setup. Don't expect the AFR to be 12.5:1 just because that's what you've set in the PCM! You need to make a run, look at the *actual* AFR and adjust the tables accordingly. Once you get it smoothed out you can adjust the AFR to best suit performance vs. safety.

The formula believed to be used by the PCM is 14.7/(1+(RPMvalue/100)+(COOLANTvalue/100))