[STi_Boy805]

I have a 2005 STi with a CAI. Every once in a while, while in 3rd gear, my boost goes from the stock PSI (14.5 - 15) to 8 PSI.
i have no leaks and i dont get a check engine light or anything.
it continues to run at 8 PSI untill i disconnect the battery and then it goes back to normal.

has anyone heard of this before?
what do you think is wrong?

Thank You!

[tnolan182]

What fuel are you using? Premium, I hope.

[STiLLawd]

CAI maybe making you run to lean when your boosting heavy and the ecu limps you.

[seanforney]

Originally Posted by STiLLawd

CAI maybe making you run to lean when your boosting heavy and the ecu limps you.

second this!

[Digitalfiend]

Assuming there is nothing wrong with your boost gauge, the only thing I can think of is that you are experiencing enough knock to drop your IAM (ignition advance multiplier) below the boost disable threshold. This will cause you to run wastegate boost levels (wastegate duty cycle set to 0 - i.e. fully open). That would be why it returns to normal when you reset the ECU; you are resetting IAM and any fine learning knock correction.

I suggest you datalog your car or take it to a tuner. If your IAM is dropping that much then you're getting a serious amount of knock.

[STi_Boy805]

I always use Premium fuel. Here in california it's 91 octane.
What causes knock or what is it?

Thank u guys/girls for the imput.
I hope that with enough information I can fix this issue.

Thank you!

[ImranM847]

Knock is the sound signature of detonation in your combustion chamber. There are a number of things that can cause this. If you're getting enough of a rattle on the knock sensor to drop your IAM down that fast, it may be real knock or it may not. Get it checked out to make sure you're engine is in good health and your tune is ok (sounds like you're stock anyway). Failing that, definitely look into the possibility of a faulty or loose knock sensor. The vibration of a loose sensor will falsly signal knock events. Good luck!

[swr999]

Originally Posted by STi_Boy805

I have a 2005 STi with a CAI. Every once in a while, while in 3rd gear, my boost goes from the stock PSI (14.5 - 15) to 8 PSI.

The 8 PSI is the mechanical action of just the wastegate when the boost control solenoid is closed (not getting actuated)...

Originally Posted by STi_Boy805

...it continues to run at 8 PSI untill i disconnect the battery and then it goes back to normal.

If the BCS is not getting actuated you would get the 8 PSI you are seeing. This could be caused by an intermittent contact somewhere in the BCS wire. But, the fact that you get ~15 PSI after resetting the ECU muddies the waters a bit

[STi_Boy805]

thank you guys/girls for the advise.
Im going to get my engine checked..
where do u think should do this.. Dealership? how much do you think it will cost.
Thanks.

[bmoreSti]

dealership will rob u blind with fees cause they r a dealership and they just can lol simply said. go to a local Subaru shop if there is one in your area that had a high rep and a good quality shop.