[jamesm]

Thanks for posting this. I'll just make two (very important) notes: first, what you're modifying here is an input to a load calculation, not a fueling calculation. Though it may not seem to matter for simple closed/open loop MAF scaling where the goal is mostly to minimize trims and get AFRs hitting targets, it's extremely important to understand conceptually. The MAF doesn't only dictate fueling, it is an input to a load calculation which dictates nearly everything the engine does in operation (like timing, port/di ratios etc). The results we see from this process with regard to fueling are only one side effect of this.

Secondly, the process as described here will work reasonably well for a vehicle with stock fueling components. To properly calibrate a vehicle with aftermarket fueling components requires process separation between port and direct injection modes. This is something that catches a lot of people off guard, particularly those who are used to tuning WRXs and think an 86 will accept the same process. There are a number of ways to accomplish proper calibration of a vehicle with aftermarket injectors, one of which is to calibrate the MAF against a fueling error log generated while running only direct injection (which in the common case has not changed), then calibrate the injectors against that known-good MAF (using the scaler and latency). Ultimately, the goal is to have extremely low fueling error on both sides of the coin. If not all sorts of awfulness ensues, like idle dipping, stalling when coming to a stop etc. I actually apply this process even when tuning cars with stock fuel systems, because I've found the stock calibration to be imbalanced by as much as 10-15%, and at that point there is a drivability win associated with correcting it.