SC fuel pump question

[bobswei]

I'm trying to figure out if the fuel pump on an SC stays on all the time or shuts off when it builds preasure? I thought it stayed on and the extra fuel that was pumped, returned back to the tank but my neighbors SC is on sometimes and off sometimes. Which is it? Thanks for the info.
Bob

[Jim Sims]

If the wiring is in OEM configuration the fuel pump should run whenever the engine is turning over and inducting air (either when running or while the starter is cranking). CIS fuel injection systems require the fuel pressure to operate so if the pump was shutting off engine performance would almost immediately deteriorate as the pressure was bled down by the operating injectors. Excess fuel is returned to the fuel tank continously so an operating CIS system never really "fills up" and shuts down the pump. If the fuel pump runs with the ignition key in the "on or run" position without the engine actually running the wiring to the air flow switch has been tampered with or has become disconnected or the switch has failed. What your friend may be hearing is not the pump shutting off but it's sound or pitch changing as the system pressurizes if the fuel pump runs without the engine running. Jim