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"I ran a LED off of one leg of the fuse to ground. When the ignition is in position II, the light comes on for a second as the pump primes. When the engine is cranking, there is no light. When the car decides to start, then the light is constant while the engine cranks."
Good analysis, but the KPII pump cycle only proves that the pump will run if the relay is energized. For starting and running (KPIII) the ECU controls the relay differently, and the ECU must get timing pulses from the ICU(REX controller). Only then will the ECU ground the Pump relay coil to activate the relay and thus the pump.
(See Start-Run sequence below.)
I tend to agree when you say: "From what i've gathered, the relay isn't getting an ECU signal to turn on the pump when cranking." If the "ECU signal" (grounding the pump relay coil at ECU terminal 21) is missing, that usually points to a failing Crank Position Sensor...
1) But you said that you're "getting spark, just no fuel".
2) If #1 is true, maybe the RSR as failing to supply 12V to the injectors.
3) But #2 can't be true if you bypassed the RSR by jumpering the two larger wires (Red and Green-Red) at the harness plug.
What have we missed?
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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 (initiate) 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.
* The System relay is in the rectangular white case with the Fuel relay.
* NOTE that on 700/900 cars with the square Hella pump relay, the RSRelay becomes the "System" relay as described above.
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, thus stopping the motor.
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Bruce Young, '93 940-NA (current), 240s (one V8), 140s, 122s, since '63.
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