read this... http://www.megamanual.com
Great write up. It actually gets into the five main circuits (power, clock, serial, input, output) and how they all work together. gets into maf vs. speed density some. Google the difference to get more info on it. I am a huge fan of the DIY efi controller. If you want low buck DIY this is it for you. Go through the MSI, MSII, MSIII, and MSPNP to see what is ideal for you. It will be a lot of hacking and splicing but worth it in the end when you can say I did this. I actually plan on designing my own someday... just cause I can... I wrote a 17 page paper for my senior seminar class for school all about the incorporation of computer controlled fuel injection systems and how the computers manage and modify fuel tables for ideal operating conditions and i get into the difference between open and closed loop operation. I plan on going through the paper and changing it for an engine croud and posting it on our wiki. I am a computer engineering student so I wrote the paper to be easy on the words for my computer friends and not engine gurus.