Now that I have my fuel pressure logging setup working, I have a question. What is the correct fuel pressure for the stock system? I know the effective pressure should be 40 psi, where effective pressure = measured pressure - boost pressure. For my 95, this is usually around 42psi up near 12psi of boost. The strange thing is that when I first get into the boost range the effective pressure is almost 50psi. It looks like it happens when the fuel pump resistor bypass turns on. It isn't just a spike either. It slowly decreases as I get into the higher boost ranges.

It seems to me that the stock fuel pressure regulator doesn't do a great job of regulation with high input fuel pressure (resistor bypass enabled). Perhaps this is why Mazda included the fuel pump resistor? It would improve low speed engine operation by keeping a constant fuel pressure. I know many people say that it is to reduce fuel pump noise and increase fuel pump service life.

 

Bump. Anybody else seen this before?