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"...after detecting or rather not detecting signal to the fuel injectors while cranking, I replaced the brain."
Could you give more detail on how you detected this failure, like what "signal" was missing?
After 7+ years with a Rex-Regina 940 and almost daily BrickBoard scans, I believe those ignition and fuel systems to be just as reliable as their Bosch counterparts. If there is a weak link it might be the Regina fuel pump, which can be iffy after 175K-200K miles—so that's a possibility. The 700/900 Radio noise Suppression Relay (or it's grounding point) could also be suspected. It gates the +12V to the injectors. Maybe the start-run sequence below will help with your trouble-shooting:
Start-Run Sequence LH2.4 or Rex-Regina
1) During starter cranking, the Crank Position Sensor sends timing pulses to Ignition Control Unit (ICU = EZK or REX)
2-a) The ICU uses these CPS pulses to trigger the Power Stage (aka Ignition Amplifier), which initiates spark from the coil.
2-b) At the same time, The ICU also propagates the pulses to the FI ECU, to allow FI operation (no ICU pulses means no Fuel).
3-a) The Fuel Injection (System)* relay (previously energized at Key On) powers the AMM, IAC, ECU, Injectors (RSRelay on 700/900 cars), and Fuel (pump) relay coil + side.
* The System relay is in the white case with the Fuel relay.
3-b) When ICU pulses are received by the FI ECU, it "energizes" the Fuel relay by grounding the relay coil (– side) to run the fuel pump(s).
When all these things work, the engine runs until the Ignition is switched off, which in turn shuts down the FI system.
P.S. Randy's tip on the RSrelay is a good one, and relates to my question about your injector diagnosis.
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Bruce Young, '93 940-NA (current), 240s (one V8), 140s, 122s, since '63.
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