Ahhh Haaa. So that's what they mean about the MAF being oversaturated. I didn't really get it the first time I read it. So the stock MAF can only read so much air coming in because of the max voltage?

 

2 reasons you can't use your stock MAF:

1. The PCM is now programmed by JDM to assume the 90mm is being used. The 90mm MAF has a different voltage vs air-flow curve than the stock one as its "full-swing" reading allows for a higher maximum air-flow

2. The stock MAF supposedly is calibrated to max out somewhere between 400 and 500 crank HP (or more correctly the air-flow required to reach those levels), so it is set to report peak voltage at those air flows... (calibration is a little sloppy up there from empircal evidence and is sensitive to DA which means it will depend on where you are and what the weather is like... )

The 90mm is calibrated to assume a higher top air-flow (thus the need to tell the PCM about the different voltage vs air-flow "transform")...

In closed loop mode (i.e. NOT WOT), I suspect the PCM will compensate and the engine will run acceptably as long as you don't floor it...

At WOT, I would expect more noticeably bad behavior as the PCM is counting on valid data from the MAF (with a "failsafe" of pulling timing if it hears a "knock").

I assume you have contacted JDM about the bad MAF - They have a good reputation, I would be surprised to hear that they leave you hanging there...

Hope you get that sorted out... I think that is now the second bad MAF out of the box I have seen around here recently... hmmm.....