Cobb's help files in ATR are very useful. They use to actually have a tuning guide that was pretty useful but I am not sure that is true any more.
There are three ways of changing fuel. That is with MAF scaling, Injector scaling, and fuel table. When all is said and done and everything is calibrated correctly, you will end up adding or removing fuel with the fuel tables, but before you get to that point, you have to calibrate your injector scale and MAF scale first. The reason for this is to get the AFR out the tail pipe to mach the AFR that the tables are referencing at that time. So the idea here is to calibrate injectors and MAF first and then tune from the AFR tables.
If you are using stock injectors, then work is done and you don't have to touch injector scale. MAF calibration should always be considered because even the stock MAF calibration is off. For calibrating the MAF, you do it in two steps. Step one is Closed Loop calibration usually normal driving and highway cruise. In this mode the ECU is referencing the stock O2 sensor and making adjustments to fuel. If you log A/F Correction and A/F Learned together and compare that to the MAF voltage being produced, the resulting error is a one to one relationship with MAF voltage. So if you have a +10% error at 2.5 volts, you simply adjust the g/s value at that voltage by +10%, there by increasing the fuel at that voltage. Once you get your fuel trims to be close to zero, you are good. It does involve a lot more than that but this is just a description of the concept. Step two is for Open Loop calibration usually on heavy and wide open throttle. It is the same concept but instead of referencing the O2 sensor, The ecu calculates fuel based on looks up values and does not take the O2 into consideration. This is dangerous because if the MAF is not calibrated properly, you could have gross errors in your final fuel. This is also why the OEM calibrates the MAF to be rich. In this mode you need to reference a wide band AFR gauge and calculate the error yourself. So you would compare your Wide Band reading to Commanded Fuel and calculate the % error. Then just make corrections to the MAF at the relevant voltage like you did for Closed Loop.
Once you are satisfied that everything is properly calibrated, then you can make changes to the AFR table to make things richer or leaner as required.
