I have now driven the car 100 miles with the megasquirt installed and have the fuel tables pretty much where they need to be. I have some knock under load under 1000rpm I need to get lined out but other than that the car is running great. But I figured it was time to share my progress with everyone here.
To put it in perspective I have modified the engine by shaving the head 0.040 to get the compression to around 10.5:1, advanced the cam slightly, ported and polished the head, free flowing exhaust, smoothed and deburred the throttle body/intake, and installed a windage tray and crank scraper. All of this made the car run pretty far out of tune, I hooked a voltmeter to the oxygen sensor and the readings were all over the place and the plugs where showing it running rich. After installing the wideband sensor it confirmed the car was running super rich and there was nothing I could do to get the factory computer back in range.
So after looking around at Megasquirt options I came across http://mtengineering.ca they have a basically plug in setup available for a metro for $325 plus shipping. firstname.lastname@example.org is his email. I got this setup and you can pretty much just unplug the factory computer and plug it in. You have to run a vacuum line from under the hood to the megasquirt though so it isn't totally plug and play but it is pretty close. Using the wideband sensor lets me set the computer up for lean burn at cruising speeds. I am running the Hires megasquirt extra code variant to get the injector timing down to a really precise number.
My current configuration as well as the HR Megasquirt installer can be downloaded so you can play with the numbers and see what is possible on this setup. I have set it reasonably conservative on the target air fuel ratio for now but I will be moving up to maybe 17.5:1 crusing after I get a MSD ignition box installed to get a good solid spark in it. Right now the car runs smoother and has more power than it has ever ran in it's life. The engine has always shook a little bit at idle and you could feel engine vibrations at speed but now it is dead smooth at idle and very smooth and noticeably quieter at speeds. I can let it idle in the yard and not make a black spot on the grass from the tailpipe. Overall I am very happy with this computer and can say that if are going for the highest mileage possible and can afford the $325 for the computer and $200 for the wideband oxygen sensor then you will pick up a pretty good gain in mileage. You will also have more information about how your engine is running and can configure all the stuff directly instead of having to trick the factory computer into doing stuff it does not want to do. Getting lean burn is simply a matter of setting your target air fuel ratio in a table and the computer will get it there for you.
I will be filling up probably tomorrow and try and get a good drive on the car to see what kind of improvement I got by installing this computer.
Here is how I modified my dashboard
The computer can show pretty much anything on the 8 gauges. Once I build a small speed sensor circuit it can give a MPG reading on one of the gauges. Then I will finally be able to actually see how my driving is affecting my mileage.
This is what I am currently driving with and will probably leave more or less alone until I get the MSD 6A installed. I do need to adjust 1500rpm column to basically the same as the 2000rpm and maybe lean out the cruising area just a tiny bit more.
I plan on raising the entire cruising area 2000-3600 x 46-55 to around 17:1 once I get the MSD in. That should give me a good jump in mileage.