learn me some fuel pump circuits

[zxtwou2]

i ran into another daunting obstacle in my quest to sort out my ITB setup with megasquirt. the British how-to i've been following shows putting a fuel pressure regulator and return line on the stock fuel rail and eliminating the fuel pressure sensor. here is the big question:

can i get away with not putting a regulator on, and just maintain the stock fuel pressure sensing system?

from the wiring diagrams i have, it looks like there are three main components in the stock circuit. first is the fuel pump module. this is the actual pump and level switch. the level switch goes only to the PCM and the instrument cluster. not sure why it goes to the PCM, but i'd like to know. the second component is the PCM. if i can bypass the PCM altogether, that would be great, but it looks like it's what ties the injection pressure sensor and the fuel tank pressure sensor in with the third component...the fuel pump driver module (that little box in the trunk.)

now how does our stock fuel system work? is our fuel pump on all the time? does it always pump at the same pressure/speed...or does it pump more as it needs more? does it cycle on or off? obviously, there has to be some control going on, since there's a fuel pressure sensor.

now...say i run the megasquirt to control injector pulses and spark timing...the basic functions of engine management. can i just leave the stock PCM there to control the fuel pump in the stock way instead of running a return line and pressure regulator with a different fuel pump? that would be best...use the stock fuel pump circuit in the PCM, and run engine management on the MS at the same time. i'm honestly just wanting to know one big question....can i run without a regulator...and run the stock circuits for fuel delivery?

[zetec00]

The pcm changes pump voltage based on load. Changes in voltage, result in changes in flow (i.e. at idle the pump voltage is low while at high rpm voltage is high). The Megasquirt Zetec write up says to leave the stock system how it is. There is a great article on how Ford's returnless fuel system works on Kenne Bell's website. Basically our fuel system has 3 components, the pump, pcm, and pressure sensor. The pressure sensor has a line to the intake manifold to read vacuum (or boost), the pcm reads this information, and alters pump voltage to maintain the correct pressure at the rail. For example, if there is 18 inches Hg at idle (1 psi atmospheric pressure = 2.036 inches Hg), then 18 inches Hg/ 2.036 =8.84. But remember that is negative pressure (vacuum), and the engine wants to suck the fuel into the cylinder, so the rail pressure only needs to see 30.12 psi fuel pressure to maintain the stock 39 psi pressure because 30.12- -8.84 = 39 psi.

[zxtwou2]

sweet. i wasn't sure, because all the ITB setups i've seen they say to use a fuel pressure regulator instead of leaving the stock system on...but none of them are for a zx2, so i didn't know if i could leave it alone. so if i leave it all stock, leave it hooked to the PCM, i'll be fine? the PCM doens't need any other inputs to adjust fuel pressure, does it? like, will i have to trick the PCM into thinking it's controlling the engine, or what?

[zetec00]

No the pressure sensor still has its vacuum signal, and thats all the pcm requires to control pump voltage.