ST165 electronics. I'm trying to figure out exactly what tells the ECU to switch between the low and high voltage circuits. From looking at the schematics, pin FPR on the ecu grounds, causing the fuel pump relay to direct power to the low voltage circuit, then breaks ground to have the relay use the high voltage circuit. But what tells the ECU to do this switch? I figured maybe the AFM when opened a certain amount would trigger the switch, but with the engine off/key on it makes no difference how far open the afm is. Maybe the engine has to be running? Cause the AFM is the only thing I can see causing the switch. I also thought throttle position could be it, but same results there. No matter how far open the tps is the ecu doesn't change, atleast when not running. Maybe I should redo my tests with the engine running.
