![]() ![]() Injector Dynamics, one of COBB’s technical partners, has a fantastic video from one of their seminars that gives a great description of fuel system pulsations, their causes and potential fixes. This gave strong indication that at least part of the issue was caused by a fuel system pulsation, which can occur for a variety of reasons. In the aftermarket, via pragmatic and observational testing, it was determined that changing or replacing the factory “octopus” style fuel pressure regulator system to more closely match the 2004-2006 STI helped alleviate the issue, sometimes to an almost undetectable level. Factory Load Compensation Table for a 2015 STI With careful tweaking or mathematical analysis tools such as that offered by the “Airboy” Spreadsheet from Sunny Lo of Airboy Tuning, these tables were able to be more closely refined, but the underlying problem (and intermittent demonstration of that issue – stumbling) was still present. They used positive values within a “Load Compensation” table to increase the final Calculated Load value, which has the net effect of artificially increasing fueling, as injector pulse width will be increased to match the new faux Load value. While not immediately harmful, this often causes an annoying feel for the driver and passengers and greatly decreases the overall quality of the daily driving experience.įrom the factory, Subaru attempted to address these lean misfire events via a tuning or ECU-side workaround. The stumble comes from the intermittent lean misfiring and the overall inconsistent fueling. One of the results of this phenomenon is noticeable stumbling or interruptions in power delivery, especially under light loads and normal “cruising” speeds. These stumbles most visibly demonstrate themselves as a high positive fuel trim (AF Correction #1), indicating a lean air-fuel ratio. ![]() Since their inception, one of the great mysteries of the 2008+ STI has always been the issue of the “2800 RPM” stumbles. By Marshall on 2008+ STI Fuel Pressure Regulator Kit Update – Technical Overview ![]()
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