Dr. Marneaus
Station Wagoneer
I've been following along for a while as well, thought I would chime in. I did a megasquirt EFI conversion on my 1973 Land Rover Series 3 with the stock 4 cylinder. Total home brew.
Your description sounds like what I had with ignition issues. Specifically, tach signal to the computer. Initially, I didn't strip the wire correctly. Tach signal wires are shielded, and I didn't strip back the shielding. So a bad connection there. Then the spade connector that connected to my coil wasn't any good! So I experienced the same problem you did, randomly, no tach signal, no injection. Like you, had no problems for a long time. Then all of a sudden, cutting in and out. Over time the connection wiggled loose and that was it.
Also I had a couple of bad coils. When the car was cold, no problems but a few miles down the road, issues.
But yes, I think ignition is where you need to be looking at. I'd start by looking at all of your connections. Do you have a way to data log? That is what will help you determine where you need to look. When you have an episode, you can see what goes to crap.
unfortunately the MSD system does not provide any external way to datalog. No way to pull info from it.