"But why do I not hear the in tank pump run with the ignition on?"

Because that's how it works on all 240's until LH2.4 came in on the 1989 models.

Neither pump should run until the ECU grounds the Fuel relay coil (terminal 85 Blue/Green), which it does during cranking and running, when it gets signals (timing pulses) from the Ignition system, indicating that it's capable of generating sparks at the coil.

The later LH2.4 has the same requirement for cranking and running. The Key On "prime" thing is not required for cranking or running, but does confirm that the pump(s) will work when the Fuel relay is energized (by unique ECU programming).

Your Main pump noise may be due to a deteriorated Tank pump outlet hose, especially with fuel levels less than 1/2 full, when the fuel from the leaky hose never leaves the tank.

Photo by Art Benstein



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Bruce Young, '93 940-NA (current), 240s (one V8), 140s, 122s, since '63.