KevinA Posted June 6, 2018 Share Posted June 6, 2018 I have a 2005 Legacy GT, with about 218,000 miles on it. Two weekends ago, I changed my fuel filter and front O2 sensor. I put the fuel pump that was in there back in, which I think was a cobb 255l that's been in there for maybe 50K. I noticed that under light acceleration the car was bucking, and sometime under heavy acceleration, the car brakes up a little before boost but usually powers through once boost comes on. I've also noticed a drop in fuel economy. from ~22mpg to ~18mpg. I hooked up my access port, and it says on at 14.5 AFR, but it seems like the car is running rich. Can someone recommend where to start troubleshooting? Link to comment Share on other sites More sharing options...
xtea Posted June 6, 2018 Share Posted June 6, 2018 Put the old front o2 back in and see what happens. Any chance you put the fuel pump back in wrong? Also reset the ecu each time if you can. Link to comment Share on other sites More sharing options...
relative4 Posted June 6, 2018 Share Posted June 6, 2018 What were the symptoms before the work? Can you provide the full list of mods? What has changed since your last tune? Can you post LV? If not, then A/F learning A-D? Any roughness (misfire) counts? Is the new O2 sensor OEM? Link to comment Share on other sites More sharing options...
leetdrv Posted June 6, 2018 Share Posted June 6, 2018 I suspect a boost leak. smoke test if you can or spray crab cleaner around IC and intake and watch AFRs or fuel trims Link to comment Share on other sites More sharing options...
KevinA Posted June 6, 2018 Author Share Posted June 6, 2018 What were the symptoms before the work? Can you provide the full list of mods? What has changed since your last tune? Can you post LV? If not, then A/F learning A-D? Any roughness (misfire) counts? Is the new O2 sensor OEM? I have a Cobb Intake, Tomei unequal length headers and uppipe, Perrin downpipe. My Last Tune was 120K ago,Mostly just maintenance, except for a lightened flywheel last time I did the clutch, and the cobb 255l fuelpump because mine failed. The O2 is a bosch from autozone. No roughness on any cyl. I'll post the LV and A/F learning A-D after I drive home tonight. I don't have the O2, it didn't cross my mind that I might need it, so I threw it out. Link to comment Share on other sites More sharing options...
relative4 Posted June 6, 2018 Share Posted June 6, 2018 The Bosch O2 sensor has to go. Denso OEM only. Also, are the new and old fuel pump the same? If not, a re-tune may be required. Link to comment Share on other sites More sharing options...
Max Capacity Posted June 6, 2018 Share Posted June 6, 2018 We all need to spend more time looking for the right parts in this thread. https://legacygt.com/forums/showthread.php/idea-web-links-saved-various-parts-219238.html 305,600miles 5/2012 ej257 short block, 8/2011 installed VF52 turbo, @20.8psi, 280whp, 300ftlbs. (SOLD). CHECK your oil, these cars use it. Engine Build - Click Here Link to comment Share on other sites More sharing options...
relative4 Posted June 6, 2018 Share Posted June 6, 2018 Right away, sire! Link to comment Share on other sites More sharing options...
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