I think there are several things that are preventing people from just throwing away their OEM ECU and running an aftermarket solution. The biggest would be good ol Johnny Law. Not only is it illegal to do emissions systems modifications in many places across the USA, but you will lose the ability to drive your vehicle after the first inspection reveals that your vehicle no longer supports OBD2, and the plugin-in test at the inspection station fails.
Another reason is the high cost of entry, both in experience and in danger. To get megasquirt running on a modern vehicle you first have to know exactly what sensors your vehicle has and what voltage range they operate and report at. This includes crank/cam pickups, air/coolant temperature sensors, and throttle position at the very least. That information is not easily available to normal users, and typically requires either expensive shop manuals or a skilled hand at a logic analyzer and scope/mulitmeter. Once you have this information you have to cut off your OEM ECU connector (thus rendering your vehicle useless for the duration) to wire it into the megasquirt or other aftermarket controller. Oh, and don't forget about removing your exhaust to weld in a wideband o2 sensor bung into your exhaust. You can do it without, but it is neither recommended or smart to attempt.
Now that you have the aftermarket controller wired into your vehicle (assuming you've gotten it started and idling successfully) now you begin the month or two long process of tuning. This often requires quite a few drive-to-datalog, analyze, retune cycles. Even in a low power engine this can be quite dangerous, as setting fuel too lean or timing too high can VERY easily cause massive amounts of destruction in your engine.
Now look at the market for CarPC people. These are a bunch of DIY guys who use their cars every day and want a better information and entertainment setup. You can install it in a weekend, and it in no way negatively affects the driveability of the car unless occasionally running without music when your pc is down counts.
Aftermarket ECU's are a whole other level of complexity and really are pointed at a different market segment from the CarPC.
That being said, I run aftermarket ECU's in three out of my five vehicles. I'm an automotive enthusiast as well as being involved in the carpc hobby, which is awesome how the two overlap for me, but I have at least one stock vehicle that I can drive while the others are inoperable due to whatever issue they may be suffering at any particular time.
It sounds like you're going for designing your own ECU, have you checked out FreeEMS? (http://www.diyefi.org/) It's an open source ECU (that I run in two of my vehicles). If you're looking for a great starting point to fiddle with, I highly recommend it as long as you understand the implications of do-it-yourself fuel injection systems.. If you're looking for an OEM replacement, spend the $10k on an AEM or equivalent. (Of course, then you wouldn't have access to the communications protocol)
Thanks for the diyefi update. I used to look at "diy-efi" until it became megasquirt whereupon the site died. But the last time I looked seriously at DIY EFI was 2005, and that was only because some newly graduated and automotive electronics industry employed self confessed expert made various claims about EMS - ie, what the could not do, or why certain things were done.
But I see DIY EFI very different other than the legal aspect, but that's why I keep to 1960's & early 1970s vehicles - in Australia they are "pre regulation" (aka pre-ADR) wrt to pollution etc. Hence I can take any modern engine, change to carbies or change EMS etc - provided I stay within capacity limits. If it was subject to ADRs (after ~1974), I wouldn't even be able to change the air filter type!
Firstly, like car audio & PCs etc, IMO you would never cut into OEM electrics. You would either use adaptors, or separate looms for more complex stuff like EMS.
Secondly, IMO you would never adapt an EMS/EFI to suit your sensors; you would get the sensors to match the EMS.
If it is a full DIY solution - ie, you are programming and constructing - then of course you can tailor the above to suit, but it might still be easier to change some components.
A classic example of the above is the common use of Delco systems. The typical scenario is to take the entire system from a suitable donor vehicle - ie, Delco sub-harness, sensors, AFM etc, distributor else ignition HEI, may be the injectors. The maps can be changed if required by various means. People can then have the entire EMS system for a few hundred dollars (based on Australian "Pick A Part" wreckers/recycler prices).
Of note, I knew several true achievers that pioneered engine enhancements etc. I watched as they pushed early manufacturers like Haltec, moved thru Autronic(?), "EMS", and whatever others I have forgotten. They all ended up using Delco systems (except for true leading edge stuff).
Since 2005 I've tried to convince others why some features show the limits or primitiveness of some (aftermarket) systems - eg, having 32 selectable maps (gained from dyno testing!). But I live in a country where dual-battery owners have been convinced they need dc-dc converters that can cost over $1,000 to "properly" or fully charge their 2nd or auxiliary batteries. As to the ability to understand EFI & EMS... [ Note - that typifies "public" web forums. Individuals can be very different, as can be private forums and groups. ]
Anyhow, my general suggestion is either Megasquirt, else Delco.
FYI - When I revisited a DIY EMS in 2005, I selected some 32 bit (ARM?) processor. I figured if my 1980's vintage distributorless ignition system (self learning etc) used a 68HC11, an equivalent EFI/EMS deserved an upgrade.
I do run aem in my AEM ACCORD. I run all aem. aem ems-4, aem epm(optical cam&crank), aem 4 channel coil driver, aem 4 channel wideband o2 controller, aem uego wideband o2, aem silkscreened full wiring harness with fuse and relay center, aem fuel rail, aem fuel pressure regulator, and aem tru-time cam gears. and I am only around $3,000 in aem products, thank you. I have a build thread here on the setup if you'd like to see. I would kill people to see what a $10,000 engine controller looks like. lol, that controller would have esp knock detection. and have a real human brain from some poor organ donor attached to it for $10,000. gosh. making sensors work is a no brainer. the vast majority of sensors work off 0-5v. and calibrating a sensor in the tuning software is easier than you think. and most tuning software is surprisingly user friendly. the tuning software usually helps and has a window to explain what each field is and does. and most even have base cal's that can be downloaded for different engines for sensors and cam and crank teeth count, just to get you started. i do not remember anybody actually plugging into my cars dlc for emissions. the way i remember it being done was with a 5 gas analyzer in the tailpipe. but with a wideband, a good cat, and a good tune there is no reason a standalone ecu can not pass emissions. even without egr. and even if the tuner were not able to setup an emission friendly tune, a little alcohol mixed with the fuel will help it burn clean. or at least that was an old trick from way back when they did still have emission testing in florida. also there is pretty much a forum for every year make and model car out there. where any and all information is readily available. you need to stop talking like we are not living in the information age. for my 5th gen Honda accord, i am a member of cd5tuner.com. when i had a 1987 Honda accord i was a member of 3geez.com. for the corvettes there is corvetteforum.com. for bmw there is bimmerforum.com. and i am sure there is a pinto forum out there somewhere, too. if you should be so lucky to own one of them. any information can be had for these vehicles in these forums. i do not think a standalone ecu is something people that have successfully built and installed a carpc should be intimidated by. and i think, nay, i KNOW from experience, that it gives the diy'er a great sense of pride everytime you turn the ignition key. it makes the whole car feel more like something you built, instead of something you bought. here are some screenshots from the aemtuner i am using.
there is work that is required to properly set one of these up. once you got everything figured out and are fluent with the tuning software the level of control you get is insane compared to tuning software for oem ecu's. the standalone's are so universal they can be used on ANYTHING. you turn on the coil and injector drivers you are gonna use, tell them what sensor they will use for feedback, then you tell the ecu at how many teeth on the crank wheel it fires each driver. it is simple math, but the ability to change that is huge. also being able to change breakpoints is incredible. on the corvettes at work i use hptuners. it is a more polished and better looking software, but doesn't allow the kind of control that the aftermarket aem controller gives. here are some screenshots of hptuners
Fwiw diyefi.org is not diy-efi. diy-efi died when the megasquirt folks killed it, and has been dead since.
Originally Posted by OldSpark
one last thing about my aem setup. the ems-4 logs data at 125 samples/sec. for 88 minutes. and it records on a loop. so anytime theres a problem, you just download the log and look at the last hour and a half of driving, with very nice resolution. this is a good and powerful diagnostic feature that also sets it apart from traditional obd. internal logging at those speeds are leaps and bounds better than looking at freeze frame data from the moment the code was thrown. aemtuner also offers pc based logging, so whenever i am tuning my vehicle(and not in real time), i log with carpc to save on time to download log from ems-4. this integration between ecu and carpc was the main goal of my build. more people should have this.