Fuel Pressure Reg Issue or other Issue?
 

While tracing another issue I have been having with my rotary, I checked fuel pressure, which opened up a new issue I didn't know I had for 3 years. I have 74PSI Fuel pressure at idle, and it drops to 68-70PSI at wide open throttle at redline. Removing the vac line to the regulator makes no change, and I am getting vacuum to it. At fuel pump prime, I am getting 55psi, and as soon as the pump shuts off, my pressure drops to 38 and holds there with the engine off. I connected the fuel pressure gauge tee'd into the fuel line between the fuel filter and fuel rail, so a plugged fuel filter would give lower pressure since I am reading fuel pressure after the filter.

Background info, this is mainly a S4 TII engine in a 93 B2200. The B2200 was originally EFI, I originally swapped a stock S4 NA motor into the truck in 2014, ran the original fuel pump for a few months, I found the fuel pump (which had 180,000 miles on it), was not supplying enough fuel pressure when the secondaries kicked on, so I changed it for a Supra fuel pump, ran that for a year, then I changed it out for a 340LPH pump last spring. I swapped the S4 TII engine in last winter.

I am running the stock fuel pressure regulator, and no pulsation dampener, stock B2200 rest of the fuel system, including the filter. Stock size rubber fuel hoses as well

I am thinking the crazy high fuel pressure is due to my fuel pump flowing more fuel than the regulator can handle, but has anybody else had this issue? I mostly see people add an adjustable fpr to increase fuel pressure for larger injectors, etc... Not due to a larger flowing pump.

what pump are you running? you'd have to have something insane like a 400lph pump to cause such a huge pressure rise.

also keep in mind, once you fix the issue you will have noticably less fuel in your tune across all RPM ranges.

I have this one, local shop carries this one, said they have had good luck with it.

https://www.performance-world.com/Fuel-Pump-p/643401.htm

thats still far too much fuel for the stock fuel pressure regulator and likely could be your problem.

you need to omit the stock FPR and put in a larger volume regulator RRFPR on there.