PWM and fuel pump wiring
Quote from 7.4 4x4 on May 15, 2020, 11:20 amQuote from bdhulderman on April 30, 2020, 8:08 amQuote from vjp38 on April 29, 2020, 4:42 pmSo I have been following this post. I have an intank warbo 255, feed my go EFI 400, with a return line. What caught my eye was the PWM. Warbo tells you to turn PWM off Or you will burn up the pump. I think I even seen if on the FiTech site. Maybe I don’t fully understand, but I am reading guys still using PWM with NON FiTech pumps. Is this a problem or internet lore?
My external pump doesn't take PWM either, so I had to wire that separately with relay from ignition so that runs all the time with the engine on. As long as your return pressure relief valve is working on your fitech, you shouldn't have an issue returning the excess fuel back to the tank. My return relief valve failed eventually, as evidenced by the fuel pressure at the inlet of the fitech going up to 100 psi, the pressure of the pump, so I had to also put in my own external pressure relief valve and return to the tank, and plug off the return line from the fitech. The advantage to this was that I could set my inlet pressure to the fitech to anything I wanted and opted for 58 psi, even though the fitech pressure relief valve was a 43 psi on the meanstreet 800 system, essentially bumping up my fuel delivery capability to 1000 hp instead of 800.
How did you know the pressure was too high at the inlet? Would adding an aftermarket fuel pressure regulator in line just before the inlet to the Fitech have avoided this issue? I'm thinking of putting a GM style adjustable regulator on the fuel line, that way the pressure would be reduced to just about what the fitech wanted prior to it getting there. I could use the same return line, I'd just have to add a couple of AN t's and the regulator and pressure gauge. Added benefit of having the ability to switch to using either system alone in a pinch if one fails. I'm trying to head off any failures while I'm hundreds of miles from the nearest gas station, now that you brought this up, I'm going to have to have a plan in case it happens to me!
Because I have a fuel pressure gauge at the fitech inlet. That's what the internal relief valve does is regulate the input pressure to what the regulator is regulated at by returning excess fuel above that pressure back to the tank.
That's what I did was to add my own external regulator to return the excess fuel back to the tank, and blocked off the fitech return with the plug. Now I could set my fitech fuel inlet pressure to whatever I wanted, and opted for 58 psi.