Bruce did a great job listing this ( Below) That's why I keep it inm my Favorites. One question though.
I can understand the ICU seeing the Cranking and sending Voltage to the Coil. I still do not understand the Amplifiers job. Does it interpret a Signal from the ICU and then release 12V to the Coil?
Which one of these starting sequences can Crap out and NOT leave a Code?


http://www.brickboard.com/RWD/volvo/1417685/740/760/780/required_startrun_sequence.html


This is what has to happen after the short pump cycle at Key On:
[You have REX ignition with Regina FI system]

Start-Run Sequence

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 Fuel operation (no ICU pulses means no Fuel 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 same white case as 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) — makes a good no-start "starting" point.

For example, if 2a fails due to a bad Power Stage/Amplifier, there will be a no-start with gas-wet plugs. If 2b fails (practically never) symptoms will be Fuel-related: a no-start with spark at the plugs, but plugs remain dry.

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