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Discussion Starter #1 (Edited)
2015-03-03 - AMMENDED - modified my setup to the following..

You need

1 foot of Vacuum Hose (1/4" Inner Diameter)
1/4 x 1/4 x 1/4 Vacuum T (Automotive Grade)
1/4 x 3/16 Reducer (Automotive Grade)
1/8 Vacuum Cap
Zip Ties

You can buy the items from your local AutoZone / Napa / OReilly's - less than 6$. Per Cobb the pressure source feeding the BPV is more consistent than the small nipple.

Fairly straight forward what needs to be done. Don't cut the hose feeding the BPV, hook it up to the T then add new hoses. Picture below is self explanatory..




Note:


The hose lengths listed in the instructions below were tested on a 2008-2015 STI.

NON-DAMPERED


DAMPERED
Background:

Stage 1 and 2 cars get the annoying stumble which is driving me nuts (Cobb AP Stage 2 ACN91). I wanted to convert to an Open Source tune using ECU FLASH and ROMRAIDER so I contacted Eric at Torqued Performance and he recommended the iAP Stumble Fix, or the Cobb Stumble Fix as a pre-requisite. I balked when I saw the price (199$ and 299$ respectively) of the stumble fix so I decided to save some money by building one myself. This particular fix gets rid of the OEM dampers on both return and feed along with the "balance" tube. It basically converts the system to a serial setup just like the older GD's. Please note that this particular fix only works on the stock setup, when one goes large injectors - seems like a different setup is needed.

Tools Needed:

2 Medium sized Zip ties
Hose Cutter
Heat Gun
Scissors
End Nipper (eq. Husky / Home Depot Model #48060 for crimping Oetiker clamps)
Parts Needed:

4 count - Dorman 800-080 Plastic Quick Connect Fuel Line Connector - around 7$ (#Dorman 800-080 - note, sold as a PAIR so only buy 2 pairs)
2 count - 1.5 Foot Fuel Injection Hose (5/16) ID - must MEET SAE 30R9 specifications - around 10$ each (#Dayco 80079)
1 count - General Purpose 1/2-inch Braided cable sleeve - 8$ (#PTN0.50BK10)
1 count - 1 Foot High Performance Silicone Vacuum Hose - 3MM ID - around 2$ (#T17932-3)
6 count - Oetiker 16700013 One Ear, Stepless, Stainless Steel Crimp On Clamps - less than 6$ for a pack of TEN (#16700013 or #B008L47GYU for a bag of 100) - Note: the size is 14.5 MM and has a range of 12mm -> 14.5mm
2 count - Corbin Clamps - 5$ for a bag of 10 (#C17611-08)
1 count - Subaru/Denso Fuel Pressure Regulator - 78$ (#22670AA351)

Alternatives to OEM part number, note - these are identical to the OEM

Standard Motor Products #PR452
AutoZone #800-564
O'Reilly Auto Parts (#BWD-24160)
1 count - M8-1.25 x 40MM Metric Flange Bolt - 2$ (#030699365586) at Home Depot
1 count - M8-1.25 Flange Nut - 1$ (#887480039184) at Home Depot
2 count - 3/4 Inch Black Heat Shrink Tubing 2$ (HST-750B) at Home Depot - Note: package comes with 2 tubes, so you need two pairs

1 count - Heavy Steel Bushing - 5/16 x 5/8 x 1 Inch (Hillman #883494 - UPC #008236921663) - 3$ (Found it at my local Ace Hardware)
OR
1 count - 1 Inch Nylon Spacer - 1$ (#887480150483) at Home Depot

Note: any 5/16 ID Fuel Injection Hose will do as long as it meets the SAE 30R9 specifications - high pressure hose.














Parts (Optional)

Standard Motor Products Fuel Pressure Damper (#FPD70 or #FPD71)
or
Airtex / Wells (#3G1069 or #3G1070)

Step 1: Disable the Fuel Pump by removing the fuse (15 amp fuse, which I'm pointing at), turn on the car until it dies. Crank it one or two more times.



Step 2: Using two zip ties, disconnect the fuel feed quick connect fitting on both the manifold and the firewall side. Make sure you have a towel handy just in case the line sputters some fuel out. You will have to do the same on the return line on both the manifold and the firewall. The return line on the firewall side is underneath the "BLUE" line pictured.





Step 3: Unclip the fuel hoses from the plastic stay, then remove the plastic stay by unclipping it from the metal bracket.



Step 4: Remove the fuel pressure regulator pressure source line by disconnecting it from both manifold and the fuel pressure regulator. It needs to be replaced as it's too short.



Note: the manifold side has a BARB, make sure you pull the hose back, and not sideways as you don't want to break / bend this BARB.


Step 5: Remove the feed and return lines along with the dampers as one unit and put it aside.



Step 6: Assemble the Feed Line - Cut one of the hoses to exactly 15 5/8 INCHES, then slide one side of the hose to the fitting. Crimp on one of the clamps at the assembled hose end. Cut the appropriate length of the braided cable sleeve which will cover the hose from clamp to clamp. Make sure you melt the edges (with a hot knife) of the braided cable sleeve to prevent it from fraying. Insert the braided cable sleeve ontop the hose, then cut two 1.5 inch strips of the heat shrink tubing. Insert the heat shrink tubing ontop the braided cable sleeve then insert another hose clamp. Attach another quick connect on the remaining hose end then crimp on the hose clamp. Position the braided cable sleeve in between the two hose clamps, center the heat shrink tubings so that it envelopes the clamps, then use a heat gun to shrink the tubing. The finished product will look something like below.

Note: the OEM feed line is 18 and 3/8 inches from fitting end to fitting end, the new one should be about the same or slightly longer. If you are adding the listed FUEL PRESSURE DAMPER noted above, then you need to cut the hose. The hose leading to the manifold should be 10 and 1/4 inch long, and the hose to the firewall should be 4 and a 1/2 inches long.




Step 7: Assemble the Return Line - Cut one of the hoses to exactly 11 and 1/4 INCHES, cut the remainder of said hose to 4 and 3/4 INCHES. Assemble as pictured below. The short hose leads to the bottom fuel return port on the firewall. The long one leads to the bottom return port on the manifold.



Step 8: Attach the quick connect clips onto the hard lines. Connect the assembled return line to both the firewall (lower port - short hose), and the manifold fuel return (lower port - long hose). Bolt the fuel pressure regulator eyelet using the bolt, the spacer, and the nut to the bracket. Make sure the quick disconnect fittings click in place on both the firewall and manifold hard lines.











Step 9: Time to install the fuel pressure regulators pressure reference hose. Remove the braid from the stock FPR pressure hose and add add it to the new hose. Attach the new hose to both the Manifold Pressure Source, and the Fuel Pressure Regulator pressure reference port. Secure the hose to the barbs by using the Corbin Clamps.







Step 10: Attach the fuel feed line to both the manifold side (top port) and the firewall side (top port). Make sure the quick connect fittings are inserted all the way and clicks into place. Add the FUEL PUMP fuse back in and close the fuse box.



Step 11: Prime the fuel system by turning your car on and off three times (but don't start it), wait at least 4 seconds in the ON position before each cycle. Feel around the clamps, hose fittings and make sure there are no leaks. Start the car and while it's idling, check for FUEL leaks - feel around the clamps, hose fittings and make sure they are dry.

Step 12: After one or two heat cycles, double check the quick connect fittings to make sure they are still snug.
 

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Please note that this particular fix only works on the stock setup, when one goes large injectors - seems like a different setup is needed.
Is that due to a flow limitation in your system? What would you change for a larger injector build?

And, by the way, thanks - nice work!
 

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Discussion Starter #4 (Edited)
Added more pics, should be complete. As for the larger injectors, everyone seems to state that the fuel rails leaves alot to be desired when using big injectors. For non-big turbo, non-larger injectors - this may be the ticket to fix the stumble along with a tune cleaning it up.
 

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Thanks for the great write-up! I am assuming this does not require any changes to tables (i.e. Load Compensation) like the fuel extension mod, correct?
 

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Discussion Starter #6
It probably needs the same thing. Eric at Torqued is asking I give him cruising data logs to button it all up.
 

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Discussion Starter #8 (Edited)
This removes the dampers, and the crossover / equalizing tube.. What is causing the stumble? Not really sure, some say it's the Fuel Rail. Nevertheless, this makes the system act just like the GD which didn't have the problem..

If someone really throws a damper into the system, Standard Motor Products FPD71 Fuel Damper Assembly is around around 38$. Needs to be installed on the "FEED" line which is easy enough to add. For something German made, check out the Bosch #0280161037 but it's pricey.

 

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Yes you would have to put it either in the feed or in the return before the regulator. If its installed after the regulator its not doing anything
 

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Discussion Starter #11
Yes you would have to put it either in the feed or in the return before the regulator. If its installed after the regulator its not doing anything
It's a bit weird though because the stock setup has a damper after the FPR..
 

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Discussion Starter #12
I wonder if the DAMPER on the return line after the OEM FPR is really that big a deal. Somebody should try just replacing the top feed line line (also removes the OEM feed line damper), capping the side / equalizer inlet port on the OEM FPR and reusing the rest of the return section. Probably even cheaper than my writeup and works the same way..

Should cost less than 40$ in parts ( 1.5 foot injection hose, 3 fuel injection clamps, Cap, 2 Dorman 800-120 Quick Connect Fittings ) easier to install and would look more OEM as you can snap the new feed hose into the plastic OEM bracket.

Hmmm, instead of capping the OEM FPR equalizer inlet port - you can probably hook it up to a fuel pressure gauge.
 

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Many cars just run a damper on the feed line only. My SHO ran a damper on the feed going into the rails, then FPR coming off the rails. When I upgraded to a parallel, return-less rail setup (return style at the regulator, just not the rails), I completely removed the damper. It ran great.

On my STi, I left the stock dampers and hard lines from the firewall to the tank.
 

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I would love to have at it but before I go for another tune I need a couple more parts. I go to Rocketrally in squamish. An a-1 top notch tuner but more rally build based and a little pricey. They stay pretty busy and not sure they can accommodate drop ins.

Really glad someone has taken a solid run at this at last. The three footer made me nervous when there was talk of the stumble just moving up the rpm range where it could become more dangerous.

Still interested in someone posting some logs and giving some feed back after some seat time.

Good stuff funks
 

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Discussion Starter #16 (Edited)
Started updating the first post, got some ideas from joejoe69 and revised the parts list to make it look more OEM.

Used the plastic quick connect fittings, oetiker crimp-on-clamps, sleeving, and heat shrink tubing. Also hooked up a setup with the fuel pressure damper on the feed line to my car and will check it out. Will also be updating the pics on the original post this upcoming Wednesday.
 

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Discussion Starter #18
Note: The hose lengths listed in the instructions in the original post were tested on a 2008-2014 STI, the 2015+ STI might may / or may not need slight alteration to the hose lengths. The 2015 looks like it has a slightly different bend on the line going from the fuel feed damper -> feed hard line on the manifold. And maybe the return line between the manifold return line -> return line damper.
 

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Been running this for a while, so far - haven't noticed the stumble along with my tune. I had some extra clamps, hoses lying around so I built two sets, one with the damper and one without..

Selling them for how much the parts cost. Not planning on making any more, i'm happy with my setup.

http://www.iwsti.com/forums/gr-engine-drivetrain-performance/275392-stumble-mod-fix-2-sets.html
Should be sending someone your way for one of these... If he does not procrastinate... Today.
 

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Discussion Starter #20 (Edited)
Should be sending someone your way for one of these... If he does not procrastinate... Today.
Only got 1 non-dampered version left, and 1 set of the dampered version. Looking for more data and feedback, not really worth it to build these things myself though and I'm finally out of sheating and oetiker clamps (yey).

I hope iaPerformance updates their kit to be more like what I documented here instead as the bolt and nylon spacer just secures the regulator better to the OEM bracket. Cobb can go to hell for charging much more money - lol. For that price, I'd go with Perrin's new PnP adjustable regulator and save a a bit more and couple it with Boomba's Fuel Rail and go parallel.
 
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