So Ive been tuning a couple of cars on the dyno as of late. Ive noticed that when Im adding or subtracing fuel im going into the maf tables. Some people said that this is ok and some have said that i should be using the air/fuel vs rpm. I looked at that table and the way the numbers are situated I dont know weather to scale them or subtract them or what?. Im more comfortable going into the maf tables,locating the gram/sec in the rpm range I need to make changes to and adding or subtracting fuel as needed. Am I wrong the way ive been going about doing this or is this just another avenue to take to get the right air/fuel. So far its been working great but if im doing something wrong please let me know.

 

Ideally you want commanded air/fuel ratio in the PE table to match reality. E.g. if your PE table is commanding a ratio of 12.7, you want the actual AFR to be 12.7, and you should adjust your MAF calibration (or VE tables) to achieve this. You can make small changes in the PE table to get it spot-on. This is one theory of tuning.

Another theory is that it doesn't matter how you achieve the desired AFR, as long as the fueling is correct under all conditions.

 

With the LT1 PCM, you're not going to be able to command a certain PE as it's a % change.
What I prefer to do is tune the MAF in open loop with the PE disabled. Dial the MAF in, then re-enable PE and closed loop and fine-tune the PE.

 

So when in the PE tables and say I want add or subtract fuel. What do you usually do?, add, subtract, or scale by a certain percentage like i do in the maf tables?.

 

LJ has a spreadsheet for adjusting the PE tables based on dyno A/F ratio results (DynoTune files).

http://para.noid.org/~lj/PCM%20Tutorial/PCMtutorial.htm

 

There's a formula for calculating the commanded AFR on the LT1:

14.7 / (1 + (% change WOT vs coolant temp / 100) + (% change at WOT vs RPM/100))

On this LT1 calibration I am looking at, the % change vs coolant temp is 16.0, and the % change vs RPM at WOT is 4.7, hence:

14.7 / (1 + (16/100) + (4.7/100)) = 14.7 / 1.207 = 12.18 AFR

Incidentally, the 1.207 is an EQ ratio, and the same approach the LS1 and later PCM/ECMs use for commanding AFR at WOT.

The big challenge is getting the commanded AFR to match what the actual AFR. For this a wideband is required, and tuning the MAF tables (or VE tables), or making adjustments to the % adjust vs RPM at WOT table is necessary.

When tuning, one approach that can be used is to modify on an AFR basis. For instance, lets say your calibration commands an AFR of 12.7, but you are actually seeing 11.7 on the wideband. If you wanted an actual AFR of 12.7, you could try commanding 13.7 with the hopes of hitting 12.7. You have to be careful though, obviously, you don't want to go too lean. It sounds like the spreadsheet that was referenced above would do this for you.

 

When put that way, I agree with you. Just putting 12.18 into the PE tables would be way too rich.

 

Yeah its a pain to calculate all this on the LT1. They made it much simpler when they switched to EQ ratios. ;-)

 

I've always dialed in the MAF table for non-PE/non-WOT throttle first...leaving it in closed loop and driving for about an hour, then coming back and looking at the recorded scan and adjusting the MAF table when the BLMs were not at 128. Reflash and do again..after about 3 iterations of this, the BLMs would be right on 128-132 at all MAF reading right up to various rpms before PE is enabled.

Once thats is done, then I hooked up the Wideband and recorded WOT passes starting from 2k rpms up to my max desired rpm..about 6200 in my case and then adjusted the "PE fueling % vs rpm" table to get the desired AFR on the wb....after adjusting the values in that table after 3 or 4 iterations I would have my desired result, 12.9-13.1 at all rpms then I'm done, provided that the spark advance is where I want it to be.