Hey, I noticed that my fuel pressure at idle is no longer 35PSI as it has been for almost 9 months now. It will go between 35 and about 41 at idle/cruise despite the vacuum staying below -20PSI. It also no longer follows the 1lb of fuel for 1 PSI of pressure as it used to (mostly) do. My questions are: 1. What is the stock idle fuel pressure (mine being 35-41) 2. What is an acceptable value for the vacuum (-20 to -22) when tapped off the blow off valve 3. Shouldn't unplugging the vacuum hose from the regulator set it at 35psi? (with the car idling) I assume the fuel pressure regulator is about to die but my air fuel is fine, especially at the top end. car drives like shit now with hesitations on throttle on/off as well as bucking under 3k. ready set go Edit: also forgot to mention i am running a walbro 255 pump, but i would love to know both stock and modded numbers if people have them. most all sites show the wrx 2L stuff which i don't think applies here.
went to classic subaru today and the tech looked up the specs. 43-43.5 PSI static so at 0psi on the gauge, it should read 43 on the fuel pressure gauge off the rail. Mine reads between 48 and 54, so it's fuxored. It will read about 35 at -20PSI idle and mine reads 40-41. I pulled the vacuum hose and it stayed there so i need a new one. it might be a tear in the diaphragm between the fuel valve and the vacuum but at this point i'm just glad i found out what was causing the rough idle and poor performance. The tech actually knew me from the auto X. I'm bad with names, sorry CooRex with an 02 wrx right?
yea that's it. classic wanted almost $400 for it but i found it online for $75 sooo.... Edit: figured i would post this here since it's good info and took me some digging to find: http://forums.nasioc.com/forums/showthread.php?s=&threadid=303644 Your fuel pressure regulator sets a static fuel pressure of 43.5psi. 43.5psi is 3 bar. Static means referenced to atmosphere. The FPR is referenced to manifold pressure/vacuum. At idle, when there is 15-18-ish inches of vacuum in the intake manifold, fuel pressure is lowered by that much. The stock FPR is a 1:1 rate. 29.92 inches = 14.7psi = 1 atm. 1 bar = 14.5psi, so it's almost a 1:1 conversion. At idle, your fuel pressure should be 35-38psi. Under boost, fuel pressure is more than 3 bar. Boost pressure + 3 bar = fuel pressure. If you're at 14.5psi boost (which is 1 bar boost), then your fuel pressure should be 4 bar. Injectors are rated at 3 bar. The stock 420cc injectors flow that much at 3 bar fuel pressure. With a 1:1 regulator, the differential pressure across the injector (fuel rail pressure - manifold pressure) remains at a constant 3 bar. Because of that, the only variable to determine fuel delivery is injector on time.