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Hi Steve,
Right after a warm start failure, pull a couple of plugs to see if they are dry vs wet with gas. That might focus things a bit.
Start-Run Sequence LH 2.4
1) During starter cranking, the Crank Position Sensor (CPS) sends timing pulses to the Ignition Control Unit (ICU).
2-a) The ICU sends these CPS pulses to the Power Stage (aka Ignition Amplifier), to initiate spark voltage pulses from the coil. The IA is built into the massive coil mount on your Rex Ign. Pretty much rock-solid compared to the more frequent Bosch IA heat sink problems.
2-b) At the same time, the ICU also propagates these CPS-based pulses to the Fuel ECU to allow FI operation (no ICU pulses means no FI operation).
3-a) The Fuel "System"* relay (previously energized at Key On) sends 12V power to the:
• Fuel ECU,
• Fuel (pump) relay coil + side (ECU controls coil ground)
• Idle Air Control valve (IAC) (ECU controls coil ground)
• 700/900 only, the Radio Suppression Relay (RSR), which in turn powers the + side of the Injectors. (injector ground side controlled by the ECU). The RSR can be by-passed with a jumper in the connector, if suspected (no fuel to plugs).
* The System (aka Main) relay is in the white case with the Fuel pump relay.
3-b) When ICU pulses are received by the FI ECU, it "energizes" the Fuel pump relay by grounding the relay coil (– side) to power the fuel pump.
When all these things work, the engine runs until the Ignition is switched off, which in turn shuts down the FI system.
--
Bruce Young, '93 940-NA (current), 240s (one V8), 140s, 122s, since '63.
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