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Old 06-05-2013, 05:08 PM   #40
Scooby Specialist
Member#: 313558
Join Date: Mar 2012
Chapter/Region: VIC
Location: Burnaby
2011 STi Sedan


Originally Posted by belaud View Post
For those that know but are not sure about the problem.

Disclaimer: This is more than clicking your seatbelt or resetting your ECU, it may permanently damage your engine or fueling system if done incorrectly.

This is the most prevalent issue with GR/GV STI's, our fueling system creates a water hammer pulsing effect which makes the car run lean and stumble from 2.4k-3.1k RPM (vehicle specific) during a light/WOT acceleration. For those that use OST, you may also notice your check engine light comes on if you cruise between 2.8k-3k RPM in 6th gear more than a few minutes with the code being P0171 of "Lean on Bank 1/2" or P0296 "Post catalyst fuel trim system too lean" . This will also fix that issue.

By lengthening our fuel line, it disrupts the pulse in the loop, creating a much smoother fuel delivery to the engine.

This guy will do a much better job at explaining than I ever will, pictures included.

Personal Conclusion
Worked for me, I had this problem under WOT as well as light load, difference was night & day, as the guide mentions, be sure to reset your ECU or if an AP is available, retune the two maps as shown. The full benefits will not show unless you retune as opposed to resetting.
Please change notation to follow syntax of above KB articles (headings/information syntax), I'll add link to the first post once changed (also, whatever you'd like to title article). All KB articles, should not contain unnecessary information/personal opinion.

WARNING: For anyone thinking about this mod (I personally don't have it, after STGII + protune but some of you may) consider that you may have to be retuned or you will run lean in the higher rev ranges due to the extended length of the fuel line. This is not only to reap the "benefits" but also to protect your car during those higher ranges.

This issue is also not usually noticed w/ stock setups, and and if observed stock, should probably be a warranty item you can take up with your dealership.
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