The "stock" OBD1 based system is giving me fits. I have no information other than a schematic with ECM1227730 printed on it. No idea if the EPROM has been altered. It worked fine last year but got crappy MPG, like 15 in moderate driving. Anyway it is running terribly now, and it seems getting a dash readout of info is not fun. I did put a wideband sensor in, it was reading 22 AFR at idle until the ECU narrow band was unplugged. Then it went to 17 which is not terrible at idle. But it still gives me no idea of what is happening and the thought of burning a chip to make changes is just so 90s. It has a crankfire wheel with 6 notches, one is a double(6 cylinder). Six separate coils already there so hopefully I can use them. The MAP and throttle body sensors are all GM, no idea what the water temp one is but there are 2 ports so it doesn't matter.
I will get the system running but something with more advanced diagnostics and self tune would be great. No need to tune for power, the motor has a cam and headers, bigger throttle body probably north of 250 HP in a 2500# car is more than enough for a 70 YO on the street.
So what are my logical candidates? Microsquirt seems to be a logical choice but what else?
I have run the 7x crank wheel with an MS3Pro using the stock ignition module for simplicity. The ignition module handled spark and sent a distributor-like signal to the computer and all ignition capable Megasquirt products can send the ignition timing "word" to the module. I am sure that half of the people on msextra are cringing at the thought 
but it worked fine for a long time for GM until OBD-II requirements made the system insufficient.
I'd look into why it's running like crap. It shouldn't run like crap and if you throw a programmable computer at it and there are issues, it will run like crap with a steep learning curve too.
If you have any exhaust leaks upstream of the oxygen sensor, you will have problems.
The throttle body must be set to read .5v on the TPS when closed. Some computer firmwares acted strangely when the throttle position was off.
The crank trigger is often called a GM 7X. MS2 and MS3 versions all support this natively. I think Speeduino does if you want a lower priced if less polished option. Otherwise native support for this crank trigger is pretty rare. There are some GM external modules (you may already have one)that read this signal and act like an HEI module to the ECU; that's going to be your best bet if your ECU can't read this trigger.
What features will you want beyond fuel and ignition control?
In reply to MadScientistMatt :
All 60 degree V6s with distributorless ignition used that setup, for a long time. When they hammered OBD-II capability into it, at first they STILL used the ignition module/7X setup with a second, high resolution crank sensor for misfire detection.
I am 99.9% sure that they used it at least up to 2005. Certainly all 3100/3400s did. At some point they switched to direct PCM control of a "dumb" coil pack, which has a single large connector to the coilpack vs. having two or three, but if the 7x is still on the crank then an old '7730 and "smart" ignition module should be able to run it no problem.
In reply to Pete. (l33t FS) :
No exhaust leaks, but the installer had questionable skills on wiring. I have had to fix several and am tired of it. The worst one was a 1/0 cable to lug that was held together with heat shrink, he may have thought he soldered, it came apart in my hands. I could be hunting for bad crimps and such forever. Combined with no dash to look at system function and very weak support it just seems inevitable.
