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Discussion Starter · #1 ·
Hello! First post here, so sorry if I dont include enough info. Basically I have a 2005 Forester XT, mostly STi conversion with a vf39 and 4EAT. It has a Stage 2 and when I hit boost of 19+ psi it sounds like pebbles or rocks hitting underneath my exhaust.

Everywhere I look says 12-15psi max is a good number to aim for, so perhaps I have too much boost? Thanks for any suggestions!
 

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2018 X3 M40i / 2016 X3 xDrive35i
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Sounds like you're hearing detonation which is a symptom of a significant issue. Are you logging it? Are you seeing knock correction?
 

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Discussion Starter · #3 ·
The more I look into it, detonation does seem to be the cause. My apologies for the misinformation earlier too, I am actually using the vf39 stage 3 tune from Cobb. I'm going to work with a pro tuner and do some logs to further diagnose the issue. No detonation under normal/mild use. Just when I really punch on the gas. Thanks for the suggestion!
 

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Discussion Starter · #4 ·
Just another update - working with a local tuner who can review some logs, I tried doing some heavy pulls to get the detonation to reappear as it didnt happen at first. Once I punched it, it threw a CEL with flashing cruise and showed me code P0304 for the cylinder 4 misfire. I guess my next thing to check would be spark plugs first? Thanks for any suggestions!
 

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2018 X3 M40i / 2016 X3 xDrive35i
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Uh oh. Spark won't usually cause detonation...it will cause a miss but severe detonation followed by a misfire code sounds more like you had a fuel problem and now the miss is telling you damage occurred. Time for a compression test and leak down.
 

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Discussion Starter · #7 ·
Just a small update: Compression test failed with 70 PSI. Getting a quote for an engine rebuilt this Monday. I got this car from Ebay for 2 grand however so I cant see myself putting over 5gs into it as it is. I might look into either just swapping in an engine or rebuilding myself.
 

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2018 X3 M40i / 2016 X3 xDrive35i
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Parting out will probably net a decent chunk of change too if you're stage 3 and patient waiting for buyers.
 
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