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Hello all, I was curious too know if there were any alternative routes into adjusting fuel pressure? I've spoken too my Tuner and said I'd have to get a Fuel Pump, Injectors and a new Fuel Pressure regulator.

I've got both the pump and injectors now but I'm standing by on the FPR because I've stumbled upon these videos.


And


Has anyone tried these? Are had a diffrent route on the After market FPR? or stumble fix?
 

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my tuner also said just the upgraded FPR is necessary, not a whole kit, so i'd listen to your tuner rather than waste money
 

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Hello all, I was curious too know if there were any alternative routes into adjusting fuel pressure? I've got both the pump and injectors now but I'm standing by on the FPR because I've stumbled upon these videos.

. . .

Has anyone tried these? Are had a different route on the After market FPR? or stumble fix?
Replace the stock non-adjustable regulator with an adjustable regulator if you want to adjust. Most people replace to handle higher fuel volume though - IE they adjust to and run the aftermarket regulator at the stock static 43.5 psi. Seems a bigger regulator helps smooth things out too.


Video #1 stumble fix incl GR load table edit. Note the guy make a lot incorrect statements right off . . . Note that:
  • GDs STI stumbled badly before there ever was a GR.
  • Stumble can always be fixed entirely All parts of the fix are part of a real build. Ealier last decade shops were still figuring this out . . .
  • Not sure about all VAs, but my stock 2020 has never stumbled, ever, at all.

Video 2 is a DIY Stumble solution , not really about adjustment.
 

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Replace the stock non-adjustable regulator with an adjustable regulator if you want to adjust. Most people replace to handle higher fuel volume though - IE they adjust to and run the aftermarket regulator at the stock static 43.5 psi. Seems a bigger regulator helps smooth things out too.


Video #1 stumble fix incl GR load table edit. Note the guy make a lot incorrect statements right off . . . Note that:
  • GDs STI stumbled badly before there ever was a GR.
  • Stumble can always be fixed entirely All parts of the fix are part of a real build. Ealier last decade shops were still figuring this out . . .
  • Not sure about all VAs, but my stock 2020 has never stumbled, ever, at all.

Video 2 is a DIY Stumble solution , not really about adjustment.
On the GD, is this the fix?: changing the fuel rails, lines (layout) and swapping to an adjustable fuel pressure regulator.

I haven't been able to find anything definitive on this on here or on NASIOC.
 

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Pretty sure GDs did not have dampers, but most people who changed the FPR, rerouted the lines and tuned had no issues. My GD was built in one pass, so I can't tell you exactly what the minimum is to cure a GDs stumble - except I don't believe the pump had anything to do with it. My car got rails in addition to the above along with a whole build. It never stumbled again though.

As in the GR, it's probably party in the tune, even if not in the load correction table. I believe there are fuel trims that are intended to compensate for the poor fuel routing.
 

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Thank you for confirming mheyman!

My 2006 came with fuel dampers on both the feed and return lines.

My car always had a very slight stumble since new.
Even when I went Cobb AP V1 stage 1 and 2 I had a very slight stumble.

When I got protuned on RomRaider/ECUFlash with a BCS and APS 70mm CAI it got a little more apparent (I assume because it got more responsive).

When I added the APS inlet (which relocated the FPR) it got more apparent.

Now a couple years ago when I went built motor, td06sl2 20g 8cm with Deatschwerks sidefeed 850cc injectors with ALL supporting mods, the stumble is VERY apparent.

What is interesting is that my stumbles occur between 2200 rpm and 3000 rpm when I am on the threshold of making positive boost pressure.
Since my car was tuned with aggressive throttle response and it spools up pretty quick, this makes the stumbles hard to drive around .
As soon as I am past 3000 rpm and in positive pressure, smooth as silk.

Thinking its time to get with yamahaSHO and swap out to Cobb AP V3 for a fresh tune and redesign the fuel system to include top feed injectors.



Back on topic with the VA STis - Apparently Subaru made some revisions starting with the 2018+ STis that address the stumbling.
 

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Stumble has never been exactly at one rpm over a specific set of conditions. Stock My 05 stumbled terribly, mostly between 2600 and 2900. But while it stumbled terribly, there were days when it didn't. Sometimes it seemed weather related, and then it would change . . . Cobb OTS stage one and two helped a bit.

Ahh - There is an important thing I left out. I always thought the stumble was related to tune, specifically the switch from closed to open loop, but "everyone fixes it" with fueling - which is surely part of the equation. When my car was built, the control was "upgraded" to Cobb hybrid, and that changes or allows changing the switch from closed to open loop . . . In my car stumble was completely exorcised. Gone. Not a sign. Ever.
 

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Hmm, interesting.

So you are tuned on hybrid Speed Density (still using the MAF for some fueling)?
 

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Yes, and I believe that these days it is the standard for a moderate and higher power street builds. I'm not sure of the exact history, but I believe it became the way to go almost 10 years ago, after Cobb made it "easy".
 

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I had 1050x injectors with a fuel pump and stumble kit (GD style FPR). The FPR kit worked with the stock injectors but with the 1050x injectors, I believe it was the culprit of a couple of issues (cold idle rpm wandering and stumbling). My tuner managed to tune out the stumble (95 - 98%) but it took some time. Recently, I installed IAG fuel lines/rails, Aeromotive FPR and I am so impressed with the positive benefit to driveability. The smoothness of the power delivery is worth it alone. Personally, I'm still kicking myself for being foolish and taking a half measure route (GD style stumble kit) instead of the proper do it once and done route (rails/lines/aeromotive FPR).
 

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I've had the issue on GD, GR and VA cars. Tried eveny combination and style of dampener, the extra fuel line mod, different tuners, etc... The best cure I've come across, is to just upgrade the regulator. My preference is Aeromotive, only because we've never once had an issue with them. They have been a set it and forget it product. Once you take this step, you will instantly regret not have done it sooner.
 
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