Quote:
Originally Posted by 76FJ55
Ok, I see that now. My mistake. I didn't look at the diagram initially as I thought you'd posted a diagram of how the F9 works.
the 87a terminal and associated yellow wire are part of the starting circuit. the yellow (bus 50) wire receives power during cranking and ensures the fuel pump runs during the cranking phase before the airflow sensor contact closes and grounds the trigger coil in the relay.
the easiest solution would be to use a diode to supply power to the fuel pump during cranking and the Hella SS relay to supply power during running.
below is a quick sketch of the circuit with the Hella relay and diode wired to the original relay socket.
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It is actually the other way around. When ignition is on, but before cranking, relay coil is energized as it receives power (+12V) on 86 from Ignition On (bus 15) and ground on 85 through the sensor plate switch, which is closed because engine is not running yet. Since coil is energized, SPDT relay switch has toggled and closes circuit between 87 (bus 50) and 30 (fuel pump positive side, not to be confused with permanent power bus 30).
So when cranking, power is applied on bus 50 (yellow wire) and goes to FP through 87-30. FP is then powered and running. As soon as engine begins to turn, airflow lifts the plate and sensor switch opens, hence the relay coil no longer receives a ground and is no longer energized. Relay switch toggles back to rest position 87a-30, which takes on to provide power to FP from bus 15.
Safety feature: in case of accident, if ignition is still on (driver unconscious), provided the engine has stalled, sensor plate switch closes again, so ground is provided to relay coil, which is therefore energized again, and relay switch toggles to 87-30, but since there is no power on 87 from yellow wire, terminal 30 has no power. Therefore FP is no longer powered and running.
I'm not sure you diagram with the diode can emulate this behavior.