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Old 07-11-2009, 09:34 AM   #1 (permalink)
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Default Wastegate Flutter?

Ever since I had my Cobb TBE exhaust installed and flashed the Cobb Stg II map, I think I've been experiencing some significant wastegate flutter.

Here are the symptoms I've noticed:

~ Ticking sound from engine bay. It's fairly loud, especially when the windows are rolled down and the sound is reflected off curbs and medians.

~ The ticking sound is only present under light/moderate load between 1,750 - 2,500 RPM. Under very light or heavy load, the ticking sound disappears. (Or maybe I can no longer hear it over my exhaust... lol)

~ I have been unable to pin-point the exact location of the sound.

~ The sound is very "mechanical." In other words, it doesn't sound like metal parts colliding.

~ Under moderate load, the engine speed varies ~200 RPM, almost like the car is surging. The surging can also be heard in the exhaust note.

~ Under light or heavy load, the surging goes away, and acceleration is smooth.



So, does this sound like wastegate flutter or something else? If it is WG flutter, I may live with it until I find a used VFxx. I plan on upgrading the TMIC, turbo, and fuel pump this Fall. Can WG flutter affect the longevity of the engine? (I've noticed it for the last 2 or 3 months) If so, I'll tighten the WG actuator arm and leave it as-is until a bigger turbo is installed. Or, I could have an EWG installed...talk about no lag and an amazing sound!

Any help would be appreciated! :)

Thanks.
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Old 07-11-2009, 03:09 PM   #2 (permalink)
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Sounds like it's the wastegate, no harm, it's just annoying.

I rode in an STi with a GT30R and EWG at the track, the sound was amazing.

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Old 07-12-2009, 04:28 AM   #3 (permalink)
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I had the same symptons with my '06 WRX with a Stage ll flash and a Cobb catted DP. I fooled with the arm adjustment and it helped a little but did not solve the problem. Then I began to wonder if it was a leak at the turbo/DP connection but could never find any signs of a leak. I finally reinstalled the stock DP, reflashed to Stage l and was happy. I actually liked Stage l better anyway in terms of overall "driveability" with Cobb's OTS maps.

I guess it's just "one of those things" with Stage ll and a TD04 on the 2.5.
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Old 07-12-2009, 06:46 AM   #4 (permalink)
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I have the same 'resonance' issue. I am running STI exhaust manifolds, HKS uppipe and DP, w/ STI cat-back. I have noticed it also. I have tuned my car, w/ E85, a couple times (252hp and 334ft-lbs), and it almost sounded like detonation. But it does not show any signs of knock. I have messed w/ less AVCS, but it didn't change the sound, but I could tell a performance difference.
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Old 07-12-2009, 07:56 AM   #5 (permalink)
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Wastegate flutter is when the boost rides a sinusodal curve, rises and falls. It sounds like your surging might be it...

But the ticking sound is not wastegate flutter, thats an exhaust leak...downpipe or uppipe gaskets, or both...
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Old 07-12-2009, 09:33 AM   #6 (permalink)
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Originally Posted by thefoos View Post
Wastegate flutter is when the boost rides a sinusodal curve, rises and falls. It sounds like your surging might be it...

But the ticking sound is not wastegate flutter, thats an exhaust leak...downpipe or uppipe gaskets, or both...
Good to know. Thanks for the heads-up. I'll stop by my mechanic this week and see if he can address is when he installs some suspension goodies.
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Old 07-12-2009, 06:41 PM   #7 (permalink)
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this noise has also driving me crazy since i put on my cobb tbe. i dont think the dp is leaking and ive never had the uppipe off. the only solution seems to throw on an ihi turbo, lol!
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Old 07-12-2009, 07:36 PM   #8 (permalink)
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Its the TDO4 wga.Its weak!

You need to upgrade into a VF39,43 or 48!!!

My wifes 04 XT with TDO4 does this & my 04 XT with VF39 does not...


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Old 07-12-2009, 08:01 PM   #9 (permalink)
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Originally Posted by fourortwowheels View Post
this noise has also driving me crazy since i put on my cobb tbe. i dont think the dp is leaking and ive never had the uppipe off. the only solution seems to throw on an ihi turbo, lol!
Quote:
Originally Posted by joe r View Post
Its the TDO4 wga.Its weak!

You need to upgrade into a VF39,43 or 48!!!

My wifes 04 XT with TDO4 does this & my 04 XT with VF39 does not...


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I'm strongly thinking about the VF39 or VF43. I just need to find one that's in good shape at a decent price.
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Old 07-13-2009, 02:14 AM   #10 (permalink)
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Originally Posted by thefoos View Post
Wastegate flutter is when the boost rides a sinusodal curve, rises and falls.
NO - what your describing is compressor surge (making a 'ch-ch-ch-ch-ch' noise like an old GroupB Quattro), frequently (and wrongly) called wastegate flutter which it is NOT.

Wastegate flutter is when exhaust pressure spikes open the wastegate when its meant to be shut, sounds like teh cobb tune may have shut the BCS at that point so the boost is sufficient to unload it enough to strat fluttering, whereas if the BCS is opened (even though nit probably won't affect boost) it means the actautor will not be unloaded slightly.

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Old 07-13-2009, 03:53 AM   #11 (permalink)
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Originally Posted by The Rookie View Post
NO - what your describing is compressor surge (making a 'ch-ch-ch-ch-ch' noise like an old GroupB Quattro), frequently (and wrongly) called wastegate flutter which it is NOT.

Wastegate flutter is when exhaust pressure spikes open the wastegate when its meant to be shut, sounds like teh cobb tune may have shut the BCS at that point so the boost is sufficient to unload it enough to strat fluttering, whereas if the BCS is opened (even though nit probably won't affect boost) it means the actautor will not be unloaded slightly.

Simon
Nope, I know what I'm talking about here Simon. Its rather unique to the TD04 that we have on the 2.5L here in the states. Subaru put on a weak 6-7 psi WGA, and when you uncork the TBE, you get what feels like compressor surge. I'll agree that it sounds like compressor surge, but its really the wastegate fluttering.

The malfunction is fixed by increasing the spring load on the wastegate, either by shortening the WGA arm, or if its really bad, replacing the WGA with a 10 psi model...
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Old 07-13-2009, 09:13 PM   #12 (permalink)
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Yes, It is the wastgate fluttering. If you hold a turbo in your hand and move the wastegate with your fingers and let it slap closed, that's the noise alright. I have been through the mill with this issue. It is described well in the first post. It started on my car as soon as the Full Cobb 3inch exhaust system was installed. I've have explored every avenue including new gaskets, tuning, the WG arm adjustment - which did help quite a bit however the noise is still pretty loud and seems to be getting slighty worse again.

You mentioned an alternative 10psi WG. could you tell me more about that. I don't really want to change the turbo because I'm already more than happy with the performance. What is the chance that this will cure the noise completely?

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Old 07-14-2009, 06:17 AM   #13 (permalink)
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Yes, It is the wastgate fluttering. If you hold a turbo in your hand and move the wastegate with your fingers and let it slap closed, that's the noise alright. I have been through the mill with this issue. It is described well in the first post. It started on my car as soon as the Full Cobb 3inch exhaust system was installed. I've have explored every avenue including new gaskets, tuning, the WG arm adjustment - which did help quite a bit however the noise is still pretty loud and seems to be getting slighty worse again.

You mentioned an alternative 10psi WG. could you tell me more about that. I don't really want to change the turbo because I'm already more than happy with the performance. What is the chance that this will cure the noise completely?

Regards
C
Its the WGA off the 02-05 2.0L TD04 turbo. I've got a thread on this site about it...they came with a 10 psi WGA.

I upgraded my turbo around 70k miles. I was able to boost up to 20 psi in the mid range with that actuator, but as I have found out recently, boosting that high reduces the turbo life...Blown oil seals at ~90k miles.
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Old 07-14-2009, 06:19 AM   #14 (permalink)
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Nope, I know what I'm talking about here Simon. Its rather unique to the TD04 that we have on the 2.5L here in the states.
OK fair enough wonder why we don't seem to get it here on 2.5 with TD04 here (later FXT and WRX).....

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Old 07-14-2009, 08:17 AM   #15 (permalink)
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I'm not sure why you guys wouldn't see it in the UK. It does seem to be down pipe related though. After installing the Cobb full system on my 2004 2.5XT I went back to the original midpipe to soften the motorway drone. That change made no difference to the flutter even with the extra back pressure.
It is also sensitive to engine and also ambient temperature. Some days loud and some not.

Regarding that alternative actuator arm, I'm not sure I want any part of 20psi. From what I'm hearing the only true fix is to revert to the original downpipe or change the turbo! ............ that's a shame.

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