Custom MAF Calibration Piggyback Adventure
 

So, I've recently built up an Arduino derivative to act as a MAF signal calibrator and mild tuning device for my non-turbo 2004 RX-8. Its capabilities overlap with things like the Australian MapEcu and various tuning devices from Greddy. It goes beyond things like the Apexi SAFC devices since it corrects based on both RPM and load. It has been spliced into the MAF signal to measure the voltage, modify it, and then send it to the ECU. It measures the RPM in real time by capturing transitions on the ignition coil igniter pin (0 to 5 V). It has a 3-D map for the MAF correction factor based on engine RPM and currently measured MAF voltage (approximately the load).

Anyway, I thought I'd start a thread on the various things I learn along the way. I'll post some plots of the data that I log, progress of the tuning and such other things.

I first started preparing for the tune in earnest last month. At that time, my LTFTs were trending in the +10 range. Before anyone calls "vacuum leak" on me, I've been through the car over and over the past year and fixed many things. I've done everything except a true smoke test and found no leaks. Also, the LTFTs were trending high everywhere not just at low RPM and light load.

About a month ago, the LTFTs looked like this (plotted using octave).
https://cimg4.ibsrv.net/gimg/www.rx8...37e6945705.png

After some tuning and relearning of the LTFTs, they look like this:

https://cimg3.ibsrv.net/gimg/www.rx8...944f97551d.png

As you can see, the trims are much lower (all within +/-3 at the moment).

Overall the car is driving much better, and it seems to me that the transition from closed loop to open loop is much smoother. The low RPM part throttle torque (what little there is) is much improved.

Not shown here is a little bit of tuning I did in the high RPM and high load areas to bring the AFRs from the 11s down into the 12-13 range. I'm still working on that part, but I have some hope that this approach nets a little bit of performance while giving me a fun project to work on.

To add some fun, here is an older data set I have showing that my engine can hit 220 g/s. A curve fit is shown that relates MAF g/s to MAF V. Ignore the stray points. I blame them on imperfect logging through my el-chepo ELM OBD2 adapter...

https://cimg5.ibsrv.net/gimg/www.rx8...16fb73140d.png

Good stuff. 220G/S is cute :)