I went with a non-PWM high pressure pump in a surge tank system with constant fuel circulation using a low pressure pusher pump mounted just outside the fuel tank.

As many know, that set-up circulates fuel at or near 0 psi from the tank to the front mounted surge tank and back to the tank at high flow rates. The fuel rails are fed by a EFI pump mounted in the surge tank and a regulator bypasses fuel from the fuel rails back into the surge tank.

The end result is cooler fuel in the fuel rails due to any fuel not shot out the injectors being constantly flushed back through the tank.

We are putting together a friends EFI system together using the recently released Pro-flo 4, a custom larger capacity Rick's stainless steel tank and an in-tank Aeromotive pump module.

His system has PWM capabilities, but we are using a bypass return regulator that is plumbed back to the tank.

It is unclear to me if using both the bypass regulator and the PWM pump control would result in unstable fuel pressure at the rails.

Interestingly to that end, I have a 2 speed Fuelabs low pressure pump on my carbureted motor controlled with a micro switch on my outboard mechanical sixpack carbs. It kicks up to high speed when the outboards are cracked.

The fuel pressure is dead stable at the bypass regulator whether on low speed or high speed. That surprised me due to the pressure and flow increase that occurs when the pump is on high speed flow. I suspect the same results with PWM and a bypass regulated set-up, but have not seen it for myself.