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Joel,
Checking the coil is a good thing but it all begins with the Crank Position Sensor (CPS). Consider the sequence below...
Start-Run Sequence LH2.4 or REX
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 (REX 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,
[and Regina RSrelay]
* 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.
Determining whether or not there is spark at the plugs (2a) — and whether or not the plugs are getting gas (3b) — is a good no-start "starting" point.
For example, if 2a fails due to a bad Ignition Amplifier, there will be a no-start with gas-wet plugs. The ICU sent "permission" pulses to the FI ECU, but has no way to know the coil didn't get triggered.
If 2b fails (practically never) symptoms will be Fuel-related: a no-start with spark at the plugs, but plugs remain dry (no CPS-ICU pulses to FI ECU).
• Is gas getting to the plugs?
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Bruce Young, '93 940-NA (current), 240s (one V8), 140s, 122s, since '63.
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