Project Miata Update

So I’ve been talking with some other Megasquirt users to request help getting into the ball park with my tune, share ideas and help validate my work so far. omgpham and Valvecovergasket were nice enough to share their tunes with me. And Reverant at MS Labs finally responded to my email with some AFR1, VE1 and Spark1 tables that were scaled for TPS. The maps in his original base tune were scaled for kpa, which is completely meaningless for Alpha-N. But he also admitted he’s never tuned an ITB car before and the tables were just best guesses.

I can’t exactly use anyone else’s tune verbatim as there are enough differences in hardware setups and personal preferences, but they do help with my understanding of the control system and the different ways people tune. Perhaps the hardest part is taking all these different data points and figuring out what elements I should incorporate into my own tune and how. MS definitely requires lots of study. Even knowing about all that you can change doesn’t necessarily teach you how to tune. The whole process is a journey, one that will hopefully make me and my car better and improve my understanding of why I’m making certain changes and what effect they’re supposed to have.

Since my last update, here are the major changes I’ve made to the base tune provided by Reverant:

– Adjust injector cc/min

– Recalculate Required Fuel

– Calibrate AFR Table (Innovate LC-2), Calibrate Thermistor Tables (Mazda RX-7 S4 & S5 CLT and GM IAT/MAT sensors)

– Lock Calibrations

– Setup Rev Limiter (fuel cut limiting only)

– Turn off Multiply MAP for pure Alpha-N control

– Incorporate AFRTarget (include)

– Change Barometric Correction Curve Settings to the new way (Tools > Calibrate MAP/BARO > the two numbers are set to 0 and 0 and the curve is normally 100% at all points)

– Setup onboard MAP sensor for realtime barometric measurement and correction instead

– Turn off Table Choices (don’t want unintended table blending)

– Turn off Launch Control (again, stripping tune down to basics so I know that other options aren’t having an undesired effect)

– Scaled VE1 table Y-axis for 0-100% TPS and populate new Z values

– Scaled Spark1 table Y-axis for 0-100% TPS and populate new Z values

– Scale AFR1 table Y-axis for 0-100% TPS and populate new Z values

– Started tuning the VE table only once engine was fully warmed up and ASE and WUE were off

I focused on the editing the VE cells around idle. I’ve found that I would have to change 4 or 5 adjacent cells a little bit at a time to get the idle closer to stoich without having random fluctuations where it would go lean. Remember, you’re never exactly in the center of a given cell even if the blue dot shows you there. It’s really a calculated figure (weighted average?) based on your actual TPS and RPM. So adjacent cells will have an affect on your current position.

Once the engine was fully warmed up (ASE off, WUE off) and I was able to very slightly open the throttle and get the RPMs above 1500 rpm I turned on VEAL and started auto tuning. Set some advanced settings for VEAL (CLT >160°F, RPM> 1500, “Cell Change Resistance” to “Easy”). The goal is to take my VE table, which is just a best guess, and adjust values so that I can step on the gas with no load in neutral and have the engine rev cleanly to redline while maintaining target AFR the entire time. Let’s just say that I’m not there yet and this is all very much a work in progress! But once I can do this, I can think about leaving the relative safety of my garage and doing some road tuning with the engine under load.

VEAL is a very nice tool to have but it isn’t a magic bullet. I find it relatively slow to change values and it does not handle transients very well. So you must be very steady and deliberate with the throttle opening to give it time to respond. Reverant said to behave as though you are driving on ice! My understanding is that you should only tune Acceleration Enrichment (for improved transient response) once your main VE table is pretty well tuned. So it is a slow, painstaking process. Despite the AFRs being all over the place I got impatient and just had to blip the throttle a few times just to finally hear those ITBs sing!


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