Back in 2005 or so, My ECM was failing in my 89. it appears similar in shape to the 93, but mine has a 14 pin connector inaddition to the 60 pin connector.
When it was failing, ususally it was the second start of the day. The relays would click on and off, the negien would stutter fart burp, occassionally backfire, and I wuold have to tap dance with the throttle just to keep it burping and farting.
Then like a switch was thrown, it would run perfectly.
The burpfart sceanario became more frequent and of longer duration until I replaced the ECM which solved the issue. I had found one wire leading to transmission had chafed and was burnt from grounding out on transmission. I thought that was the cause of the demise. Might have been.
My 14 pin connector was also problematic with techs piercing the insulationat the connector. the wires rotted and broke and my get me home fix was to drill out the failed wire through socket, strip wire, push it through and reseat connector.
This aided in destroying the solder joints on the pins, which I resoldered 2 years ago without a stall/no restart situation since.
Some of the 14 pins were fairly wobbly before resoldering when grabbed by tweezers. They are much larger than the pins on the 60 pin connector though
You said you have a backup ECM. Next no start, swap it in.
Ram4Ever has ben trying to school me on capacitors, and it seems that they are lucky to be able to function properly at all at their advanced age.
I have my original failed ECM, and at some point will try replacing all the capacitors and see if it works again. I was unaware of it in 2005 when my ecm was failing, but I am pretty sure the issue was the ECM was not able to hold the ASD relay closed. Pretty easy to bypass a relay with a jumper. I did so later when the relay itself failed, but the fuel pump would run continuously even with key out of the ignition so I had to keep opening hood and disconnecting jumper after stopping the engine, and returning it to drive, until I bought another common relay.
On some jeep forums there are reports similar to yours/mine about the nostart situation and replaced capacitors being the fix. In their case the capacitor ends had bulged in an obvious failure.
None of the capacitors in my failed ECM have obvious visual failures.
You will see that the jeep ecm looks nearly exactly like yours:
http://www.jeepforum.com/forum/f13/fixing-lazy-pcm-new-caps-writeup-501951/