I recently constructed a flex fuel tune for my 2001 Silverado 1500HD from a 2001 Tahoe flex fuel file and segment swapping the 4L80E code from a 2002 Avalanche with an 8.1L. I adjusted for cylinder volume, tuned the VE, PE, and whole bunch of other tables and the truck runs great, except for initial start. I attached a log showing it is super rich at startup (10:1 on gasoline scale) and stumbles for about 2 seconds at startup then runs great as the AFR comes more in line. There are a lot of cranking airflow and cranking fuel tables, so I'm trying to figure out how the whole thing works. I'm guessing the ECU takes all these airflow tables/adders to set an initial position on the IAC? However, the fuel that is dumped in is all based on the cranking fuel tables? So if I'm too rich, I need to concentrate on reducing the cranking fuel? I know the ECU can't be using the MAF, because it's not warmed up for initial startup.
I also want to understand how the FA multiplier table works. Is it a multiplier on the VE table or something else? Those numbers are big. Also, the first and second pulse masses seem to play a role in this as well. I was going to zero them to see if it makes any difference in startup AFR. From reading the forums, most people multiple the FA table by 1.2 for Flex fuel applications. That made things worse for me as I'm guessing it was dumping in even more fuel and I'm already too rich.
Any help on a plan of attack or understanding of how the fuel and airflow are utilized would be helpful. Thanks.
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