I've been looking for information related to DIY tweaking of the 2.5l Mazda L5-VE engine control unit in my '10 Mazda3 s Sport. I don't expect to go anywhere near it just now, but someday, who knows. What I've found, so far:
There are one or two tuning shops or services out there on the forums/Internets that have offered this service. With at least one, you do have to remove the ECU and ship it to them, I assume along with logged realtime wideband O2, EGT, etc. performance data generated using the right kind of dynometer. Dynatronics (San Antonio, TX) is one such shop, having announced the "MZR 2.5l" ECU was format was 'cracked' this past July.
The Tactrix Openport 2.0 may have evolved around Subaru and Mitsubishi platforms, but it appears to have been used successfully on some recent Mazdas. The Epifan EcuEdit project may have started in the Subaru camp, but has branched out to MazdaEdit, whose 2009 compatibility included 1st mazdaspeeds, CX7, RX8, mazda3, mazda6, and the mx-5.
This is bleeding edge stuff, and it's not clear to me from what I've found there is support for 2nd gen mazda3's yet, including out 2.5l L5-VE's ECU. It isn't clear if that means the hardware interface won't work to read/write the firmware tables, or if it's that they're in a format and/or envelope that hasn't been deciphered yet. This isn't surprising, if the 1st gen layout as described by dynotronics is any indication: "thing is, the MZ3 has something like 83 maps for the early model, and the ms3, has over 200! So you have to be able to find the correct map to do what you want, and I can tell you, it ain't easy!" Suffice to say, if the MazdaEdit software hasn't been developed to support the L5-VE, assuming you can still read the tables, you're potentially talking about some hex editor fun just to hopefully figure it out. Even if it does work, anecdotal evidence suggests it's only marginally more helpful than the hex editor. Unfortunately, your car's engine is the alpha test, so this is not really 'consumer-friendly.' Apparently this all came about by Mazda and Subaru both using "Denso with a Renesas SHxxxx chipset" ECUs. Anyway, even if all this matures a bit, or has matured, to a nice editing interface, it's still essentially brain surgery on your ECU's programming; it takes methodical care and access to the right dynometer to come up with alternate values for the ECU tables.
I'm hopeful that there'll be some nicely polished affordable software to do it, and that tune shops in general start offering it. If you need the dynometer anyway, that'd be the obvious place to get an engine tuned, right? But having the software yourself for minor tweaks and to track changes, verify tuning changes, well, that couldn't hurt, could it?
But yeah, what the others said, relatively speaking, this is probably not a performance mod starting spot. But the above stuff and similar projects seem totally worth keeping an eye on over the next few years.
