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1) Crank Position Sensor generates timing pulses to Ignition ICU
2a) ICU propagates timing pulses to Power Stage to trigger spark at coil
2b) ICU also propagates pulses to FI ECU to allow FI operation
3a) FI ECU energizes fuel relay (Fuel Relay has two outputs, 3b and 3c)
3b) Fuel relay sends +12V to pumps
3c) Fuel relay also powers AMM, IAC, ECU, Injectors
Knowing whether or not there is spark at the plugs—and whether or not the plugs are getting gas—will allow some analysis of this sequence.
For example, if 2a fails due to a bad Power Stage, there is a no-start with soaked plugs.
If 2b fails (practically never) symptoms will be like 3a below
3a fails = a no-start with spark at the plugs, but plugs remain dry.
Etc.
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Bruce Young '93 940-NA (current), 240s (one V8), 140s, 122s, since '63.
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