Jump to content
LegacyGT.com

The famous stumble...fixed?


Recommended Posts

Please do me and I'm sure others here a favor and document this install with some picture and final parts list/sources. Every time I look at the FPR I just see spaghetti.

 

What do you plan to do with Cylinder 4. Will you cap it or use it to feed a boost gauge?

 

I have pictures of everything I did earlier in this thread. Though photobucket might have killed the links.

 

In which case I might just do a tech write up in the How to Section with hosted links.

 

UPDATE: Took the how to's from my build thread and made a new how to post with everything in one location. Photobucket photos still work, but I will have to upload them to the site later.

How To: Install 04-07 STI Fuel Pressure Regulator (FPR) and Use a New Vacuum Source

Edited by covertrussian

05 LGT 16G 14psi 290whp/30mpg (SOLD)

12 OBP Stock 130whp/27mpg@87 Oct

00 G20t GT28r 10psi 250whp/36mpg

22 Ascent STOCK

Link to comment
Share on other sites

  • Replies 377
  • Created
  • Last Reply

Top Posters In This Topic

Question.

Looking at the COBB stumble fix install guide, it says to install the FRP with the vacuum port on the bottom. But most of the images I can find on this site have the vacuum port on the top, is there a reason for this?

631353571_ScreenShot2017-07-31at5_18_12PM.thumb.png.012277c5a79f1e8ac6238a1b6eeac7e1.png

Link to comment
Share on other sites

According to the parts diagram, it's actually "on its side". So that's a third orientation, so I'm guessing it doesn't matter?

 

I was also trying to figure out if there was a flow direction for it.

From the parts diagram, if the flow is leaving the rail and heading to the left, the 90 bend is input. Where as the COBB install has the 90 bend as output...

138041144_ScreenShot2017-08-01at10_51_43AM.thumb.png.ffdb77e7ddc2ec1b9411932568830474.png

Link to comment
Share on other sites

That's actually from a WRX, which is slightly different then STI.

 

My input (from engine) is into the center of the the FPR, and output (going to fuel tank) is the 90* bend. Been working correctly, Cobb one pictured above is exactly how mine is hooked up too.

05 LGT 16G 14psi 290whp/30mpg (SOLD)

12 OBP Stock 130whp/27mpg@87 Oct

00 G20t GT28r 10psi 250whp/36mpg

22 Ascent STOCK

Link to comment
Share on other sites

Good to know on the flow direction, thanks!

 

Interesting, that's from parts.subaru.com for the '05 STi. I double and triple checked it. Now, if look it up in the '05 STi service manual, the FPR looks totally different. I'm not sure why.

 

The parts diagram for '07 STi looks like the service manual, but there is only one nipple for fuel as it bolts to the rail on a flange, however, the part number is exactly the same as the '04-06 STi "22670AA351" that is what I have and what COBB uses and has two fuel nipples for connecting lines.

 

http://parts.subaru.com/p/Subaru_2005_STI25L-TURBO-6MT-4WDSEDAN/REGULATOR-ASSEMBLY-PRESSURE/49232576/22670AA351.html

Edited by Infosecdad
Link to comment
Share on other sites

Finished my install of the '05 STi FPR for my '05 LGT.

Was fairly easy to do, took a couple hours all told. Removed the full FPR and delivery/return dampers assembly. Made a single replacement line for the delivery side and reused the existing hoses for the return side. Made a simple mount for the FPR and installed it in a similar manner to the COBB instructions. About $2 in nylon space, bolt, and chunk of metal for the mount. Picked up a plastic Fuel Line Disconnect from Pep Boys and shaved the nose of it so that it was easier to get jammed in around the stupid lip by the firewall. The engine side didn't have that lip, was super easy to do by comparison.

 

Initial drive was very promising, noticeably smoother in the 2k RPM range, especially with little to moderate load. Relearned idle much quicker this time, compared to previous ECU resets. Will hold off declaring it a complete success until I've driven it for a bit.

 

IMG_3877.thumb.JPG.c60329850a9fdf05159ae74ca1b09323.JPG

 

IMG_3878.thumb.JPG.b8b78ae9a3d91530d319de77fef3fe52.JPG

 

IMG_3879.thumb.JPG.5ca676efeb717cad94142f3c211e4786.JPG

 

IMG_3881.thumb.JPG.23ef3c0b827d21842925e9ee22f18773.JPG

 

FRP Reference:

http://parts.subaru.com/p/Subaru_2005_STI25L-TURBO-6MT-4WDSEDAN/REGULATOR-ASSEMBLY-PRESSURE/49232576/22670AA351.html

Edited by Infosecdad
Link to comment
Share on other sites

I think I know why Cobb says to install it upside down. The vacuum feed would hit the strut tower otherwise. That's why I used channel locks to rotate it a bit, and then no need to install it upside-down.

 

http://legacygt.com/forums/attachment.php?attachmentid=253376&stc=1&d=1501640928

http://legacygt.com/forums/attachment.php?attachmentid=253377&stc=1&d=1501640928

05 LGT 16G 14psi 290whp/30mpg (SOLD)

12 OBP Stock 130whp/27mpg@87 Oct

00 G20t GT28r 10psi 250whp/36mpg

22 Ascent STOCK

Link to comment
Share on other sites

  • 3 weeks later...

 

And these: McMaster high temp silicone cap

 

Edit... Just did TurkeyLord tap off the Bypass valve to the FPR. Temporarily, I found an assortment pack of the nipple caps at AutoZone. I measured the cyl 4 output at 0.25 OD and the kit has 0.25 caps. But 7/32 seemed to fit tighter with a zip tie. I know that these are known to fail over time from engine heat. I am hoping this is temporary and I get motivated to install a boost gauge finally.

 

From a very short drive up my road, the stumble at 2500RPM under load seems better. I'm going to do an engine reset and keep an eye on things.

Edited by ashwinearl
Link to comment
Share on other sites

Updated my STi FPR by adding the previous (post FPR) fuel dampener back in line. I was getting a lot of odd noises that I wasn't crazy about without it. Much quieter now, and I feel that the fuel delivery is better.

 

I flipped the FPR over and made a shorter quick disconnect line for the return hard line on the intake, put the FPR inline, then a short run to the dampener, then to the stock quick disconnect line. Made a small bracket to hold the dampener and it's good to go.

 

IMG_3905.thumb.JPG.50953f0cd0013d78e6170b1f393adc3d.JPG

Link to comment
Share on other sites

Just so you know, that damper is set on the fuel pressure regular exit, not entry, which means it's dampening the fuel that's going back to the tank and not going to the engine.

 

Which begs the question, why did it help? Your FPR must be pulsating causing the noise.

05 LGT 16G 14psi 290whp/30mpg (SOLD)

12 OBP Stock 130whp/27mpg@87 Oct

00 G20t GT28r 10psi 250whp/36mpg

22 Ascent STOCK

Link to comment
Share on other sites

Yeah, that's the damper that is was on the return line (and is again). The damper from the source line is still sitting in the stock assembly on my shelf. I'm not the first to find there are interesting noises coming from having just the STi FPR with without any dampers. My experience was similar to this post:

 

http://legacygt.com/forums/showthread.php/noise-after-fueling-changes-254016.html?t=254016

Link to comment
Share on other sites

That's so weird! I wonder if your vacuum line is resonating, causing the FPR to open and close a lot (creating the noise).

 

Also I have an in bay fuel filter, on the entry, this might work as a resonance chamber and it does store extra fuel right next to the engine.

 

Finally are you on the stock fuel pump? I personally am so that might be another reason for no noise.

05 LGT 16G 14psi 290whp/30mpg (SOLD)

12 OBP Stock 130whp/27mpg@87 Oct

00 G20t GT28r 10psi 250whp/36mpg

22 Ascent STOCK

Link to comment
Share on other sites

I would be willing to bet that your in-bay filter is an amazing damper. I've been tempted to do something similar.

 

I'm running a AEM 50-1000 pump with freshly cleaned stock injectors. I've capped the previous vacuum feed on intake #4 and tee'd off the reference line for the BPV.

 

Without the damper, at idle it almost sounded like I had an exhaust leak. At 2k RPM it was lost in other sounds, don't know if it went away or was just drowned out.

Link to comment
Share on other sites

I also do have a fuel pressure regulator, which could function as a damper of sorts too (because diaphragm and gauge spring).

 

But back to fuel filters are dampers, my 04 FXT had dampers and fuel filter in the engine bay too.

05 LGT 16G 14psi 290whp/30mpg (SOLD)

12 OBP Stock 130whp/27mpg@87 Oct

00 G20t GT28r 10psi 250whp/36mpg

22 Ascent STOCK

Link to comment
Share on other sites

Mine made the odd swishing swooshing noises at idle, which was probably the only downside I had experienced, and it was a very small issue. Reading these comments, perhaps a damper would have solved it.

 

One little curiosity was that it only made the noise at idle when the fuel pump duty cycle was 33% (watching the values) and when you'd lean into the throttle and the duty cycle went up, the noise would stop. But if a damper solves it, then that sounds like a great solution.

BtSsm - Android app/Bluetooth adapter. LV, logging, gauges and more. For 05-14 Legacy (GT, 2.5, 3.0, 3.6), 02-14 WRX, 04-14 STi, 04-14 FXT, 05-09 OBXT
Link to comment
Share on other sites

  • 1 year later...

I posted several pages back about my fuel setup on my etuned stg2 LGT. Sti FPR, BOV reference line for FPR and slightly longer fuel hoses. Ive had the stumble for quite awhile since I last posted. None of the above took care of it completely. Im at the point where Im looking for answers and found this on one of the romraider forums. http://www.romraider.com/forum/viewtopic.php?f=15&t=4911&hilit=stumble&start=285

 

Recently I added more hose (3ft) to the inlet side of the fuel rail fitting and reset the ecu. It was much smoother after the reset but I can tell its relearning the stumble again after only a few miles. I know M Sprank talked about blocking out the learning capabilities of the ecu for that area of the tune. Has anyone ran a t-style fitting on the inlet hose to stop the water hammer effect? Am I understanding the cause of the stumble correctly??? TIA

 

One other question. Im not sure if this is just me or what but I also feel that different brand fuels cause the stumble to be more or less pronounced. Am I crazy? Lol

Edited by oncesir
Link to comment
Share on other sites

Do you experience oscillating love/hate emotions towards your LGT, and yet you still keep the car? If yes, then you're probably crazy like the rest of us.

 

Thats a great way to describe it. I'm extremely picky about the running condition of my cars and the stumble is like having an unresolved problem. Aside from that I love the car. Its fun, handles decently and has never left me. Its had its usual 4th gen issues but thats more just repairs based on age.

 

I will say that after adding the 3 ft of inlet hose to the fuel line that the stumble is still relatively minimal. It comes and goes but is definitely less than it was before. Maybe Ill add a fuel pressure gauge on the inlet side and see if that helps. Before this is all said and done Ill have 50 different fuel dampers, gauges and other BS in that 3 ft of hose just to remedy this one issue.

Link to comment
Share on other sites

Not sure if this has ever been attempted (many many posts on this stumble), but has anyone ever tried to put a "damper" on the FPR signal line?
BtSsm - Android app/Bluetooth adapter. LV, logging, gauges and more. For 05-14 Legacy (GT, 2.5, 3.0, 3.6), 02-14 WRX, 04-14 STi, 04-14 FXT, 05-09 OBXT
Link to comment
Share on other sites

Dont need to. Just relocate the vacuum reference. You want the plenum, not a single runner close to the valves.

 

 

Thanks, I did do that years ago and it helped tremendously. But I still see people occasionally posting about still having some stumble even after having done that (and switching to an 07 FPR on earlier models). Just wondering if those outlier might want to try a damper on the FPR signal line - just a wild guess of an idea :)

BtSsm - Android app/Bluetooth adapter. LV, logging, gauges and more. For 05-14 Legacy (GT, 2.5, 3.0, 3.6), 02-14 WRX, 04-14 STi, 04-14 FXT, 05-09 OBXT
Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now



×
×
  • Create New...

Important Information

Terms of Use