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Hey guys, STi owner here, but having trouble that I think you guys will have more experience with...
I have a dual in-tank surge tank by Taarks and only currently running one Walbro 450 lph running 100% and the second pump is hooked up, but will run either off of an Arduino using PWM, or a Hobbs switch.
In the factory fuel tank is another Walbro 450 lph wired to run 100%.
My return line T's to my flex fuel sensor, so it's not restricting the flow. Then it goes to my surge tank. The overflow from the surge tank goes to a -6 AN line to the factory return line by the firewall.
Fuel lines are -6 AN from the firewall through the engine. Factory hard lines back to the fuel tank.
The problem is that my base fuel pressure starts at say 43 psi, then 55 with the car running, and when I rev the engine, fuel pressure goes DOWN instead of up.
It seems like there's a restriction on the return line causing back pressure. Radium makes a Venturi jet pump to replace the factory one in the fuel canister, but instead of doing that, I drilled a hole just above the factory Venturi unit to relieve pressure. Doesn't seem to have helped much.
What's your guys' experience with adding more pumps? What am I not thinking of?
Fuel pressure was fine before this with just the single Walbro in the fuel tank.
What size is the factory line from the firewall back to the tank? What size is the hole in the siphon in the factory fuel tank? What fuel pressure regulator are you using on the fuel rail?
What size is the factory line from the firewall back to the tank? What size is the hole in the siphon in the factory fuel tank? What fuel pressure regulator are you using on the fuel rail?
Factory lines are just a little under 3/8" i believe. Aeromotive FPR. Not sure on the hole size of the siphon.
The siphon in the stock tank probably needs to be about 7-9/64's. Once that hardwired walbro 450 fills the surge tank, it is definitely over running the factory return line and pressurizing the surge tank.
It doesn't make sense that fuel pressure goes up when you start the car, vs key on engine off condition. It should go down when you apply vacuum to the regulator.
It looks like my Aeromotive 13109 FPR is the restriction. Any recommendations on higher flowing FOR using -6 fittings? Return line hole (in center) is tiny.
Is that part of the fitting? That should be 6an sized, the ID of a 6an fitting is ~.344". That fitting looks small. I have car in the shop right now running dual bosch 044's that doesn't have any fuel pressure issues.
Jan 26, 2017, 09:32 AM
