Changed to LS1 MAF- now fuel trims are slightly off. Remedy?

[dlagrua]

Engine 2006 3800SC. Changed to an SLP LS1 MAF, N* TB, free flow 3" exhaust, 3.4" pulley.
Was trying to tweak the stock GTP MAF table to work with little success so we imported the LS1 MAF table into the program and it improved things dramatically. Now the fuel trims look far better but not perfect. Set the trims to zero and went driving for about 35 minutes. STFT's ranged from 0 to about 3 but most of the histogram showed numbers in the cells around 2 or 3. This seems to be pretty decent. However, the LTFT's were averaging around 10 and if you add things up and we are 13% off the mark.
Could use some tips on tweaking the LTFT's. It appears that we need to slightly bump up some of the flow rates in the MAF curve but by how much? The LTFT's average about 10 while the STFT's look to be close. so do we raise the select MAF curve values by 2-3 ( the STFT no) or by 10 ( the LTFT no.) Comments would be appreciated.
Dennis
Hillsborough, NJ
HP Tuners VCM suite user

[darkdragon]

You would have to increase the MAF flow by the LTFT value. The STFT's will always trend towards 0 since they are used to calculate the LTFT. Here's a good starting point:

http://www.hollandms.com/newbie/tuning_new.htm

In addition, use the LTFT vs MAF frequency histogram. If you don't have one, I've attached one below.

[EaglePerformance]

By changing the MAF, you have changed the air flow or more correctly, how the computer "sees" it. You need to re-calibrate for the new setup, bringing the actual A/F into line with the commanded A/F by using the MAF transfer function, and running the car at load through all the load points for the MAF. Use the percent difference between the actual A/F and the commanded A/F and change the MAF #s the same amount.

[dlagrua]

On another post here a tuner advised increasing the MAF values about 1/2 of the value that the average LTFT's were off ( lean). This seems to have worked as we are now between 0-2 on all cells. Now we are scanning and looking at the PE adder vs RPM to get that area right but we can probably only get close until we buy a wideband O2. Thanks Dragon for the link and for the MAF histogram. The info on that link is really helpful.