... systematically elimināte other possibilities ...
First, any and all suggestions are welcome. If I may say, this DIY project is much more necessity than ego - I really do like the car (I have owned it since it was new), but I am on very limited income (small pension and social security) with a lot of expenses (wife is battling cancer). This is only car I have with working A/C and it has some other new parts and has been very reliable. I am a relic of the 1960s muscle car era (have a '68 Barracuda) - I have a lot of experience working on cars/engines, but before the computerized era. I am also a retired electronics engineer, so I know embedded computers inside/out (in general, not automotive specific), but the lack of comprehensive/exhaustive documentation and x-ray vision is a real limiting factor. It would also help if I was much smaller and could fit into all these nooks and crannies where things are.
If I may reiterate, I am still pretty sure the PCM is inoperative, although I can't prove it is defective, yet.
Just to review and get back on level footing, here is a list of what I think are the relavent symptoms (most already stated, some new):
1. When key/ign is first turned ON (engine OFF, and in START), there is no CEL/SES/MIL light on instrument cluster. There should be.
2. With my Innova 3040 scan tool plugged in to DLC or Diag Port, it lights up (getting power) but when key is turned to ON, it attempts to link with computer but cannot - after a few seconds, it returns a "failure to communicate" error. PCM must not be online.
3. While cranking, there is no fuel, spark, or injector pulses. I only traced the fuel pump enable signal back to the output of the PCM; if I ground this signal, the fuel pump runs and fuel flows plentifully to the rails and out the pressure test port. PCM does not seem to be generating any signals needed to run the engine (at least in the case of fuel supply, everything downstream is working properly).
4. I have checked and there is an EEC power signal (+12V) coming out of the CCRM going to power the PCM. I have checked all fuses and they are all good.
(I didn't see the need to further trace the ignition/injector problem, since it seemed at this point that some kind of PCM failure was evident.)
5. When key/ign is first turned ON (enhine OFF, and in START), engine fan comes on and runs at low speed. No shutoff signal from PCM.
Now, I am basically just ringing out all the wiring to/from the PCM (looking for a fault that is disabling the PCM or that may have damaged the PCM; this is only reason I haven't just bought a new one to test with). If it's an open ground or something like that, hopefully it will be easy to find. I am hoping that I may still find something that I messed up when I had the dashboard out.
I am looking for some place to take the PCM to have it tested - that knowledge would help me know where to concentrate my efforts. But I haven't any place that has the equipment to test PCMs.
The biggest thing that would help me right now (I think), would be a list of signals and sensors that connect to the PCM and what kind of reading would be expected in a static state. I could probably create a signal list from the documentation I have, but I don't have a pre-existing comprehensive understanding of the mechanics/electronics behind every single sensor on the vehicle.
Again, if it looks like there is something I've overlooked, please mention it. Any ideas, even shots in the dark, are welcome.