Something is a little off

[mightyS]

It has been running well without problems since June when I had it modified to a stage 2.5. Just recently it started making a little humming/moaning sound only at max boost. Normally I don't hear it. If I give it some gas and get the boost up some, it still sounds normal. It only makes the sound starting around 4000 rpms at full boost. It is noticeable when in 4th gear at 2000 rpms (40 mph) and I floor it. At first, there is no humming, but around 3500 rpms it starts and keeps going until I let off the gas a bit. I can also hear it at WOT in 2nd and 3rd gears but the roar of the engine drowns it out. It seems to be comming from the drivers side. Any ideas what it is? I plugged in the Cobb AP and it shows the car is making 17.5 lbs of boost (normal for my tune).

 

This car has an AVO TMIC, STi up pipe, Cobb catted downpipe, light crank pulley, and the Crawford A/O separator.

 

I checked the bolts on the TMIC and all seemed tight. I can't tell if it is a boost leak, an exhaust leak or something else. Any ideas?

[The_Bishop]

FWIW - Check that all your clamps are tight. I had a leak between the TMIC and the intake that presented itself as a noise when on boost.

 

When you said the "bolts on the TMIC" were tight, I wasn't sure if we were talking the same thing or not.

 

- Allen.

[mightyS]

I tightened the clamp from the TMIC to the intake. Then I checked it and it made the sound again. Now it only seems to be making the sound during the turbo lag stage (floor it at 2000 rpms and let the boost build).

[The_Bishop]

I know you said that your boost was indicating what's expected for your tune, but I'm still on the "leak" line of thinking. Assuming you installed the AVO TMIC yourself, is the seal present between the turbo and the inlet side of the TMIC? I know you said that everything was tight, but just making sure all the seals are present..

 

Only other thing I can think of is making sure that the rubber seal that is at the TMIC outlet/intake connection is seated proprely and not doubled up or blown out. I found it a little challenging to get the outlet of the TMIC seated securely and even if your clamp appears to be tight in this area, a doubling up of the seal could be causing some of the boost to bypass and cause a noise.

 

it doesn't take much to remove the TMIC...you could always take it off and check all the DP, UP connections to the turbo from above just as a double check, and carefully re-install the TMIC. Just seems to me that with all the joints that were distrubed while upgrading to the stageII stuff, things just need a sanity check.

 

- Allen.

[mightyS]

Thanks for your help. I didn't install any of the parts. I paid a mechanic at a speed shop to do the work. He was experienced with the STi/WRX but had not worked on a Legacy. I only have a socket wrench set -no torque wrench- so I was checking the bolts by feel. I tested the car again yesterday. At full power from a stop I took it up to 7000 rpms from 1st to 3rd. There was no odd noise, just the roar of the engine. Wow that thing is fast. Then I tried it again at 2000 rpms in 4th and it made that little hum again.

[mightyS]

I was going to take the car to a shop and have them do a boost leak check. Then I found the bolts that secure the blow off valve to the TMIC were lose. I tightened them and the leak noise stopped. I'm happy, especially since the shop wanted to charge an hour of labor to do the boost leak check.