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"Can a defective crank position sensor prevent the coil from producing a spark?"
It not only can, but definitely will. The CPS is where it all starts, as in the sequence below:
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 FI operation).
3-a) The Fuel Injection (System)* relay (previously energized at Key On) powers the AMM, IAC, ECU, Injectors, and Fuel (pump) relay coil + side.
(Also the Radio Suppression Relay on 700/900.)
* 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 pumps.
When all these things work, the engine runs until the Ignition is switched off, which in turn shuts down the FI system.
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The RS Relay powers the injectors and (on 7/9 turbos) the coil as well.
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Bruce Young, '93 940-NA (current), 240s (one V8), 140s, 122s, since '63.
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