I upgraded to an FD pump & had a hell of a time starting.
It flooded every time.
I found the problem - a leaking injector.

Now it starts cold, but floods on hot restarts.

I finally installed a push button circuit from the start wire to a relay to ground the pump's resistor relay.
Now I can hold low voltage to the pump for hot restarts.

One little upgrade can take a full day & 3 evenings.

 

I find that very interesting. I installed one on my S5 TII 2 years and never encountered any problems. The FD pump doesn't push that much fuel to overpower the regulator like a Walbro, so what do you believe caused the problem. Do you believe it could be the 12 volts that you have directed to pump at all times? Just curious.
I have never seen the flow rates on the Mazda pumps, but I do have all 3 Mazda pumps in the garage n/a, TII, and 2 other FD pumps, and always wanted to check the flow, but have never found the time or energy, but maybe oneday.

 

From what I've read & observed, the pump voltage goes high when cranking & when under boost.
It flooded on the very first attempt to start after the pump swap, so I suspect I had a weak primary injector.

The FD pump is stronger, but who knows what the specs are?

Anyway, that fixed the cold start flooding.

My spare 4 injectors are going to crusinperformance after he replies my e-mail.