"Okay, so if I follow right, it seems like a crank sensor issue, however, with a faulty crank sensor, starter fluid wouldn't make it turn over due to no spark."
• I agree. And that logic points to a fuel problem, which could be related to the Pump relay, or even possibly it's companion the System relay (which among other things picks the RSR and powers the ECU). Or the RSR itself. Or the RSR coil grounding tab (which bit me once).

"I'm assuming the power stage is the same way, in that there would also be no spark, and you wouldn't be able to start the car with start fluid."
• Right again.

"Am I right so far? "
• Yes, but I'm not leaning towards anything "Regina" ECU related yet. I've had my '93 940 for over 10 years now, and have scanned this board almost daily to gain "synthetic" 740/940 experience, which tells me the controllers are absolutely the last place I'd expect a problem.

"When I get my next no-start, I'm going to test Regina contacts 1 and 5 (ground), for 7-8 volts when the starter is cranking. Also, I'm going to test contacts 20 and 5, with ignition on (position II) for battery voltage."
• ECU 1 receives the REX timing pulses, so the "OK on starting fluid" theory says the pulses were received OK.
ECU 5 leads to a static ground within the ECU and never known to fail.
ECU 20 is a static ground for the Pump relay coil. It could cause a fuel problem but not likely. That box is a solid as they come, IMO.

"Are there any other contacts I should be testing on the Rex and/or Regina units?"
• Not that I can think of. I'd be more inclined to focus on the Pump relay and RSR. You said you'd bypassed "both of them", but without knowing the specifics of how you did the bypassing, I'd like to suggest what has worked for me.
Forcing the Pump relay — See THIS POST, noting that if the pump is good, it will run as soon as the "rigged" relay is plugged in. Since the relay is hard to get at, you can use fuse 11 to control the pump.
EDIT: I'm not suggesting this as a fix, but a diagnostic to help localize the problem.

Bypassing the RSR — I'm not sure if you jumpered a temporary connection between the two larger wires (RED and RED-GREEN) at the relay harness plug. I made up a jumper for mine using an old power window switch. The terminals are the same size as the bigger RSR ones, making a good fit in the relay socket. I soldered a connecting strip of copper and covered with tape. Here's a pic...



I'm not suggesting you do the same, just showing what worked for me. My jumper has been in place for about 3 years now, making the circuit similar to the 240 LH2.2 and 2.4, which don't have an RSR at all.


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Bruce Young, '93 940-NA (current), 240s (one V8), 140s, 122s, since '63.