I haven’t posted in awhile but here we go. 04 STi with some fueling issues. I’m in the process of replacing my fuel pressure regulator and now I’ve got some questions. Now as some of you know the FPR is under the intake manifold on the STi. I’m planning on installing the OEM part but seeing if it would be wise to spend the extra and get an aftermarket one. I’m planning on selling the car and it will return to mostly stock. So I’m not sure if it’s a plus to save the next owner the headache or if I’d be creating a headache for myself relocating with an aftermarket FPR. Next question is pertaining to general maintenance to anything under the manifold. Is there anything I should replace while I have it pulled off? Thanks! *fuel system is all stock minus the walbro fuel pump.*
As far as I know, there is not a "plug n play" aftermarket option for 04-07 STi because the reg bolts directly to and is fed directly from the fuel rail. I believe 08+ the regulator is actually on the fuel return hose (not directly on the rail), which Cobb makes a direct plug and play replacement for. Any option will require custom AN hoses and AN fittings to adapt it to the regulator. I'm not sure anyone makes one (you could get creative and make one), but you would have to bypass the stock FPR. You can see how it bolts to the rail in the pic below and fuel flows in the direction of the arrows. You'd need to find a solution that would allow you to still bolt a pipe to where the stock FPR bolts to the rail, but without the FPR diaphragm in it. It would just exit the rail and continue on... Then the fuel would exit the stock fuel lines where the Feed/Return/Evap exit from the manifold (see pic below). From the "RET" line above, you would have to adapt from that stock hard line to the aftermarket reg. (perhaps a fitting like this one: https://www.summitracing.com/parts/rus-640863 (this may not be the correct size for that line...it's likely smaller than 5/16) You could potentially use push-loc AN fittings that would adapt a rubber hose to an AN fitting. Then you'd have to adapt from the exit of the FPR to the return hard line on the firewall that goes back to the gas tank. That part that I linked above will fit on the firewall hard lines (5/16 quick connect to AN adapter) Hopefully that's not super confusing. It probably is, I apologize...just kind of spitballing ideas. I'd never thought what it would take to do this without also changing to aftermarket rails; in which case would use all new AN lines and fittings anyway. At that point plumbing an aftermarket FPR would be much easier since it would remove all of the stock fuel lines and rails from the equation. Perhaps someone has a simpler solution. Otherwise, I'd suggest just replacing it with a stock reg. While you have the manifold off, inspect for any cracked rubber lines and tighten any fuel clamps. They like to seep fuel (right behind the alternator) especially in the winter when everything is tight and shrunk up (commonly fuel smell inside cabin).
https://www.iagperformance.com/IAG-90-OEM-Fuel-Rail-Adapter-FPR-WRX-STI-p/iag-afd-2004bk.htm Didn't realize this existed. -6 AN ORB adapter. Then you could just go AN from this adapter, to the aftermaket reg, then adapt to the return hard line at the firewall. IAG Adapter >>> -6 AN ORB >>> -6 AN hose end >>> -6 hose >>> -6 AN hose end (possibly a 90?) >>> -6 AN ORB >>> FPR >>> -6 AN ORB >>> -6 AN hose end (probably a 90) >>> -6 hose >>> -6 AN hose end (straight or 90) >>> lastly, the 5/16 quick connect to -6 AN adapter on the stock return hard line at the firewall (linked to summit in previous post) Easy. LOL Edit: Would also need a -6 AN ORB plug since you'd still be running the rails in series and you'd have to plug one port on the FPR https://www.summitracing.com/parts/EAR-AT581406ERL This is the FPR that I use and would probably recommend if you go the aftermarket route https://www.summitracing.com/parts/AEI-13109
@joebush44 thanks for the response. But all that seems to be more than what I want to get into since it’s getting sold. I hope others find this thread useful.
Lots of fuel pressure regulator adapters out there, as many manufacturers use the same basic 2-bolt regulator bolted right to the rail. Some adapt to hose barb, some NPT, some AN, etc. Something like this: https://www.ebay.com/itm/Fuel-Press...pQAAOSwItJafpAQ:sc:USPSFirstClass!55779!US!-1 I'm a big proponent of the parallel fuel rail mod on turbo Subarus. And while that's not exactly difficult, probably doesn't make sense unless you're looking down the road at more modifications.