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This question has been on my mind for a while, so I thought I would ask. I left my fuel pump circuit alone for my EFI conversion; but that seems to differ from the norm, as most, if not all, of the rest of you, are controlling the fuel pump via Megasquirt. Is there any advantage to this?
Functionally the two functions are overlapping identical functions. The megasquirt has the advantage of always (no matter what) priming upon powerup. Though if you by chance already have Dave's digital RPM relay that point is moot since his does too. Leaving it separate means you do not needs to do any additional wiring or add relays. If you wired the pump up to the megasquirt you would need to wire in an additional relay from MS with power in either from a new fused 12V or the RPM relay socket, and outputting to the RPM relay socket. If you already have a wideband O2 sensor on the fuel pump output from megasquirt you'll still want a separate relay for the pump. Do NOT share pump power and O2 sensor power. Way too noisy.
Personally, I just liked having all of my fuel/spark functions in one place. No "hybrid" with the stock D systems. The car only provides me with power (x2), a wire to the fuel pump and a ground. My MS setup does the rest, including fusing.
I left my RPM relay in place. Honestly after all the K-Jet troubleshooting I had (and buying Dave's solid state relay) I figured it was less mental gymnastics to learn a new set of troubleshooting and modify the wiring even MORE.
If I were doing it over I'd probably do it all the way through MS, but I'd also be running a lot more than just the fuel pump through it.
I would pull the rpm relay (bypass it) if Megasquirt shuts off power to the fuel pump when the car isn't running. It makes no sense to have an extra point of failure if Megasquirt is just duplicating the function of the rpm relay.