7427 upgrade tuning help understanding

[Neukam]

Your Idle VE table looks very lumpy. When you look at the table graph, your values should have a nice smooth transition without large peaks or valleys.

Remember that the computer is interpolating between 4 adjacent cells at any given time to do it's calculations. For example, at 700 RPM at 40ish MAP, your computer is calculating using an interpolated value based on the 600 and 800 RPM rows in the 40 column and also the 35 or 50 column depending on which side of 40 MAP that it's reading at that instant.

Your values in the 40 column for 600 and 800 are 50.4 and 44.9. The idle speed is always changing slightly, even as normal operation, and the computer will continually try to self correct. As the idle speed drops, it's interpolating the values from the table and reading that VE is rising, therefore making the engine run richer, causing vacuum to drop, shifting towards a higher load cell with a higher VE value, causing the engine to run even richer as the IAC opens to prevent a stall, it overshoots and sends you near the 50 MAP 1200 RPM cell where the engine leans out and trys to stabilize, but fails to and the cycle repeats. That is what I suspect is happening.

I suggest raising your Maximum MPH for Idle VE and Maximum TPS for Idle VE temporarily to allow you to stay in the idle VE table at various speeds and loads and spend some time dialing this in. Whether you tune with your wideband or unlocking and using BLMs, be sure to smooth out your table and do a quick sanity check to make sure the values are moving in the right direction. For the most part, higher MAP, or higher RPM will result in higher VE, especially with your idle map that maxes out at 1800 RPM, you're not going to be hitting any airflow restrictions that would significantly skew your VE.

Attached is my Idle VE table. It's not perfect, but its in the ballpark and is a lot closer than the factory table was. Block Learn will take care of the rest. Notice the trend from low MAP, low RPM, low VE to high MAP, high RPM, high VE and smooth transitions. You can disregard the fact that the 100 column dips down and it really shouldn't, but thats how it was from GM and I didn't bother with it because realistically, it'll be running on the Open throttle table before I get anywhere near that column. I suspect that was the engineer's thought as well.