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Hi Fred,
You've done a nice job of troubleshooting. The LH 2.2 pump doesn't "buzz" at Key On, but you should be able to hear/feel the System relay click. [EDIT: There are 2 relays inside that case: System and Fuel.] The System relay coil + side has constant 12V from the 25 amp blade fuse, and the CU should ground it at 86/1 (like your ground jumper) when it "sees" Key On 12V at pin 18.
I don't think this is a "known" ECU problem like the ECU's occasional failure to ground-pick the Fuel relay at 86/2.
Ii seems like the Key On 12V at ECU 18 is OK, because from there it also connects to Fuel relay coil + at terminal 85 — and the Fuel relay works when you supply the "missing" ECU ground for the System relay at 86/1, allowing the car to start.
The diagram shows a straight Y/Black wire from ECU 21 to System relay 86/1, so it looks like either an internal ECU problem, or the contact at either end of that grounding wire. [I assume you hear the System relay click when you apply the ground at 86/1 with Key On?]
As for "steps" to take, I'd say it's most probably a bad relay — something a visual check doesn't show. IMO that would be much more likely than an ECU failure, and my first step would be to replace it.
Temporarily you could "back-probe" connect a ground to 86/1, and control it with a switch for safety till you get another relay to try.
--
Bruce Young, '93 940-NA (current), 240s (one V8), 140s, 122s, since '63.
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