Legacy GT Flutter Sound at Specific Speeds

[ColbyMP]

Okay, I am the third owner of a 2010 LGT with 159,000 miles. As far as I know, it has some tune to the computers but virtually all stock mechanics. Today, I noticed a brand new noise that resembles a turbo flutter. It occurs at specifics speeds in each gear when I rev higher than needed before shifting (around 2,500 RPMs). I hear it best in 4th from 40-45 mph, 5th from 50-55 mph, and 6th from 60-65 mph. It occurs both when accelerating (harder than normal; doesn’t do it when slowly accelerating) and coasting while the engine is breaking. It only occurs at those speeds and goes away beyond them. For example, I am in 4th accelerating around 35 mph and hear the typical, consistent turbo whistle. Then, I reach 40 mph and hear a flutter-like whistle or squeal until 45 mph, then it goes away. Then I let off the throttle and at 45 mph, I hear it again until 40 mph, but it is a fainter sound than when accelerating. It sounds like either the turbo or maybe a belt. Could it be a wastegate actuator? Or just a sign of an old turbo? (I think it’s the original turbo). I have no smoke coming from the exhaust and there is no obvious loss in power. I don’t have a boost gauge so I’m not sure what psi the turbo is producing. Please help diagnose the issue. I’ll post updates if I resolve it. Thanks! Edited April 28, 2020 by ColbyMP

[stewdogg]

Can you capture the noise on video?

[poconoracing]

Okay, I am the third owner of a 2010 LGT with 159,000 miles. As far as I know, it has some tune to the computers but virtually all stock mechanics. Today, I noticed a brand new noise that resembles a turbo flutter. It occurs at specifics speeds in each gear when I rev higher than needed before shifting (around 2,500 RPMs). I hear it best in 4th from 40-45 mph, 5th from 50-55 mph, and 6th from 60-65 mph. It occurs both when accelerating (harder than normal; doesn’t do it when slowly accelerating) and coasting while the engine is breaking. It only occurs at those speeds and goes away beyond them. For example, I am in 4th accelerating around 35 mph and hear the typical, consistent turbo whistle. Then, I reach 40 mph and hear a flutter-like whistle or squeal until 45 mph, then it goes away. Then I let off the throttle and at 45 mph, I hear it again until 40 mph, but it is a fainter sound than when accelerating. It sounds like either the turbo or maybe a belt. Could it be a wastegate actuator? Or just a sign of an old turbo? (I think it’s the original turbo). I have no smoke coming from the exhaust and there is no obvious loss in power. I don’t have a boost gauge so I’m not sure what psi the turbo is producing. Please help diagnose the issue. I’ll post updates if I resolve it. Thanks!

 

Definitely get an sound clip of it and post it.

 

Compressor Surge or 'flutter' sort sounds like a rattlesnake, or a muted Choo-Chooo-Choo? It happens when the throttle plate slams shut on the release of the throttle pedal (like it would when you shift), while the compressor is still producing boost. Said another way the turbo is stuffing air into the intake, the throttle plate closes and that air has no where to go, the turbo wheel is still trying to stuff the air and it cavitates/stalls (the sound you hear) until it slows down. Its no good for the turbo in the long run so fixing it is important.

 

I've never heard it specifically on our cars, but its a pretty consistent sound across all the turbo systems I've heard it in.

 

It would be caused by the re-circulation valve (IE BPV) either not recirculating fast enough, or not enough volume to reduce the back pressure in the intake, or not at all. It's job is to route pressure from the charge pipe to the intake when the intake pressure is too high. Basically in a circle until the wheel slows down and the pressure falls.

 

So Do this:

 

Use your phone and record the sound and upload it

 

Take the intake hose off the turbo inlet. The inlet is the hard plastic piece on the shiny side of the tubro. With the engine cold! Look down the inlet and you will see the end of the turbo shaft. Stick you hand in there and see if the shaft moves in and out or up and down. it should not be sloppy. Assuming no issues, put the intake hose back on and secure

 

Check the vacuum line that runs from the top of the BPV to the intake. Make sure it is secure, no cracks in the hose etc. Take a can of brake cleaner and squirt both ends of the hose and any suspect areas with the car idling. if when you spray the idle goes up you have a vacuum leak.

 

Assuming vacuum the BPV is good you likely have a failed or failing recirculation valve. Its about $100 and easy to replace.

 

I used this one -

 

https://smile.amazon.com/gp/product/B004PPXGH0/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

 

Or

 

OEM PN# Part Number: 14471AA230 Valve Air Bypass.

Edited April 28, 2020 by poconoracing

[ColbyMP]

Can you capture the noise on video?

 

It is a pretty quiet noise compared to my loud Invidia cat-back and Invidia Catless DP. I tried getting audio but the sound is inaudible.

[ColbyMP]

Definitely get an sound clip of it and post it.

 

Compressor Surge or 'flutter' sort sounds like a rattlesnake, or a muted Choo-Chooo-Choo? It happens when the throttle plate slams shut on the release of the throttle pedal (like it would when you shift), while the compressor is still producing boost. Said another way the turbo is stuffing air into the intake, the throttle plate closes and that air has no where to go, the turbo wheel is still trying to stuff the air and it cavitates/stalls (the sound you hear) until it slows down. Its no good for the turbo in the long run so fixing it is important.

 

I've never heard it specifically on our cars, but its a pretty consistent sound across all the turbo systems I've heard it in.

 

It would be caused by the re-circulation valve (IE BPV) either not recirculating fast enough, or not enough volume to reduce the back pressure in the intake, or not at all. It's job is to route pressure from the charge pipe to the intake when the intake pressure is too high. Basically in a circle until the wheel slows down and the pressure falls.

 

So Do this:

 

Use your phone and record the sound and upload it

 

Take the intake hose off the turbo inlet. The inlet is the hard plastic piece on the shiny side of the tubro. With the engine cold! Look down the inlet and you will see the end of the turbo shaft. Stick you hand in there and see if the shaft moves in and out or up and down. it should not be sloppy. Assuming no issues, put the intake hose back on and secure

 

Check the vacuum line that runs from the top of the BPV to the intake. Make sure it is secure, no cracks in the hose etc. Take a can of brake cleaner and squirt both ends of the hose and any suspect areas with the car idling. if when you spray the idle goes up you have a vacuum leak.

 

Assuming vacuum the BPV is good you likely have a failed or failing recirculation valve. Its about $100 and easy to replace.

 

I used this one -

 

https://smile.amazon.com/gp/product/B004PPXGH0/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

 

Or

 

OEM PN# Part Number: 14471AA230 Valve Air Bypass.

 

Thank you for your detailed response and help. It’s great to know people care about each other and their cars on here. As far as getting an audio, it is a pretty quiet noise compared to my loud Invidia cat-back and Invidia Catless DP. I tried getting audio but the sound is inaudible. I will try a few more times. I will certainly try the methods you prescribed and see if it is the recirc valve. Would it just be worth it to instead replace the whole turbo since it has so many miles on it? Would a new recirc valve come with a new turbo? Thanks!

[poconoracing]

Thank you for your detailed response and help. It’s great to know people care about each other and their cars on here. As far as getting an audio, it is a pretty quiet noise compared to my loud Invidia cat-back and Invidia Catless DP. I tried getting audio but the sound is inaudible. I will try a few more times. I will certainly try the methods you prescribed and see if it is the recirc valve. Would it just be worth it to instead replace the whole turbo since it has so many miles on it? Would a new recirc valve come with a new turbo? Thanks!

 

If you are tuned for a catless J-Pipe (AKA downpipe) - yes just replace it if you still have the OEM. Odds are you are running higher than stock boost and the OEM valve does not like that very much.

 

If its aftermarket pull it off and consult the manufacturers website on how to clean/service it. They get gummed up over time. Also make sure you check that vaccuum line. No/low vacuum mean it doesn't open on time. The line I'm talking blew off mine while tuning - pics attached

Edited April 28, 2020 by poconoracing

[ColbyMP]

If you are tuned for a catless J-Pipe (AKA downpipe) - yes just replace it if you still have the OEM. Odds are you are running higher than stock boost and the OEM valve does not like that very much.

 

If its aftermarket pull it off and consult the manufacturers website on how to clean/service it. They get gummed up over time. Also make sure you check that vaccuum line. No/low vacuum mean it doesn't open on time. The line I'm talking blew off mine while tuning - pics attached

 

Unfortunately, the previous owner has the stock exhaust. I am unaware of it having an aftermarket recirc valve but I’ll check it out. I’ve had the car for 4 months now and yesterday was the first I’ve ever heard this sound. Is it possible the valve just got tired over time and finally gave up? Or would it have been doing it the whole time if it was due to my exhaust and overboost? Thanks again!

[dgoodhue]

I hear it best in 4th from 40-45 mph, 5th from 50-55 mph, and 6th from 60-65 mph. It occurs both when accelerating (harder than normal; doesn’t do it when slowly accelerating)

 

It seem like you have a few mods and a tune. You really should NOT be doing low rpm, high boost accelerating. High boost levels of a tune, a low mount relatively small turbo with dual AVCS allow our engine to do this. This can cause a condition LSPI. LSPI breaks connecting rods in the FA20DIT (2015+) WRX's.

 

Do you have Cobb AP to log the engine, I wonder if your be hearing detonation on acceleration. That doesn't explain deceleration. though.

 

Has your engine had its timing belt changed? and if so what brand of timing belts was used? I never hear my car flutter, I have a tune and Invidia exhaust. Any chance that your air box came loose?

 

The BPV doesn't come with the turbo.

[dgoodhue]

The BPV leaks and reduces your boost, it isn't going to cause overboost.

[stewdogg]

There's always this fart producer you could check as well.

 

 

 

This is the pipe between the intercooler and intake. They came with a short rubber sleeve on both ends from the factory. There have been a number of people around here with a failure of this particular part.

Not sure it's your issue, but something else to check out.

[stewdogg]

It seem like you have a few mods and a tune. You really should NOT be doing low rpm, high boost accelerating. High boost levels of a tune, a low mount relatively small turbo with dual AVCS allow our engine to do this. This can cause a condition LSPI. LSPI breaks connecting rods in the FA20DIT (2015+) WRX's.

 

Do you have Cobb AP to log the engine, I wonder if your be hearing detonation on acceleration. That doesn't explain deceleration. though.

 

Has your engine had its timing belt changed? and if so what brand of timing belts was used? I never hear my car flutter, I have a tune and Invidia exhaust. Any chance that your air box came loose?

 

The BPV doesn't come with the turbo.

 

It certainly would be helpful to be able to check boost and knock. With those miles it could be anything.

 

 

ColbyMP, what percentage of throttle are you giving the car when the noise happens?

It sounds more rotational to me due to the certain speeds and RPM's that it happens when accelerating or decelerating. It doesn't seem like it need to be under boost to happen...? It's also a pretty small window that you are actually hearing the noise...

 

Any engine noise under the hood at idle?

[poconoracing]

The BPV leaks and reduces your boost, it isn't going to cause overboost.

 

If it's leaking yes, you would have low boost.

 

If it's stuck closed or slow to open? That it's job, to open and relieve to boost pressure in the charge pipe when the manifold reaches high vacuum on a closed throttle plate and the charge pipe has positive pressure on the other side of the throttle plate. The definition of compressor surge.

 

OP is talking about a noise between shifts after boost. It's when the BPV does its thing, sudden throttle plate closure while the turbo is still spinning

Edited April 28, 2020 by poconoracing

[ColbyMP]

It seem like you have a few mods and a tune. You really should NOT be doing low rpm, high boost accelerating. High boost levels of a tune, a low mount relatively small turbo with dual AVCS allow our engine to do this. This can cause a condition LSPI. LSPI breaks connecting rods in the FA20DIT (2015+) WRX's.

 

Do you have Cobb AP to log the engine, I wonder if your be hearing detonation on acceleration. That doesn't explain deceleration. though.

 

Has your engine had its timing belt changed? and if so what brand of timing belts was used? I never hear my car flutter, I have a tune and Invidia exhaust. Any chance that your air box came loose?

 

The BPV doesn't come with the turbo.

 

I am unaware of what tune my car has. I was just told by the dealership that the previous owner tuned the computers. I think the timing belt is due for a change so I’ll look into that and the air box. Thanks.

Edited April 28, 2020 by ColbyMP

[ColbyMP]

There's always this fart producer you could check as well.

 

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[ATTACH]284242[/ATTACH]

 

This is the pipe between the intercooler and intake. They came with a short rubber sleeve on both ends from the factory. There have been a number of people around here with a failure of this particular part.

Not sure it's your issue, but something else to check out.

 

Thanks a lot, I’ll look into it.

[ColbyMP]

It certainly would be helpful to be able to check boost and knock. With those miles it could be anything.

 

 

ColbyMP, what percentage of throttle are you giving the car when the noise happens?

It sounds more rotational to me due to the certain speeds and RPM's that it happens when accelerating or decelerating. It doesn't seem like it need to be under boost to happen...? It's also a pretty small window that you are actually hearing the noise...

 

Any engine noise under the hood at idle?

 

It occurs before boost. I’m not giving it much more than half throttle. No noise when idling under the hood.

[ColbyMP]

If it's leaking yes, you would have low boost.

 

If it's stuck closed or slow to open? That it's job, to open and relieve to boost pressure in the charge pipe when the manifold reaches high vacuum on a closed throttle plate and the charge pipe has positive pressure on the other side of the throttle plate. The definition of compressor surge.

 

OP is talking about a noise between shifts after boost. It's when the BPV does its thing, sudden throttle plate closure while the turbo is still spinning

 

Thank you for the info. All great stuff to look into. Wish I had a boost gauge. It doesn’t do it between shifts.

[ColbyMP]

So I did some more research and found that a bad TMIC to TB hose sound is what my car sounds like. I checked and sure enough, the hose was bad. I ordered an AVO TB hose, installed it, and the sound is STILL HERE UGH At this point, still not sure what the issue is. I tried my best to capture a sound clip of it so attached is the clip. Not sure if you will be able to hear it or not. It is the whistle flutter sound right before shifting: http:// https://streamable.com/un7zax

Please help. Thanks.

The following link is a different person’s video of their 2011 WRX doing the same thing. Mine sounds just like this: https://streamable.com/3wkt7

Edited May 7, 2020 by ColbyMP

[FLlegacy]

So I did some more research and found that a bad TMIC to TB hose sound is what my car sounds like. I checked and sure enough, the hose was bad. I ordered an AVO TB hose, installed it, and the sound is STILL HERE UGH At this point, still not sure what the issue is. I tried my best to capture a sound clip of it so attached is the clip. Not sure if you will be able to hear it or not. It is the whistle flutter sound right before shifting: http:// https://streamable.com/un7zax

Please help. Thanks.

The following link is a different person’s video of their 2011 WRX doing the same thing. Mine sounds just like this: https://streamable.com/3wkt7

 

You need to do a boost leak test. I did mine by removing the aircleaner box and plugging the opening with a snack container then feeding in air through the reference line of the bpv, with an air compressor. Low pressure like 5-10 psi.

[ColbyMP]

You need to do a boost leak test. I did mine by removing the aircleaner box and plugging the opening with a snack container then feeding in air through the reference line of the bpv, with an air compressor. Low pressure like 5-10 psi.

 

Yep, doing research I found that a boost leak is a high probability. I’ll check it out. Thanks for the info on how you did yours.

[dudemonster]

So I did some more research and found that a bad TMIC to TB hose sound is what my car sounds like. I checked and sure enough, the hose was bad. I ordered an AVO TB hose, installed it, and the sound is STILL HERE UGH At this point, still not sure what the issue is. I tried my best to capture a sound clip of it so attached is the clip. Not sure if you will be able to hear it or not. It is the whistle flutter sound right before shifting: http:// https://streamable.com/un7zax

Please help. Thanks.

The following link is a different person’s video of their 2011 WRX doing the same thing. Mine sounds just like this: https://streamable.com/3wkt7

 

You were going to have to address that IC-TB hose sleeve lameness anyway, so not a wasted effort.

[ColbyMP]

You were going to have to address that IC-TB hose sleeve lameness anyway, so not a wasted effort.

 

Agreed! Just wish the issue was solved. Gotta hunt around for a boost leak.

[ColbyMP]

You need to do a boost leak test. I did mine by removing the aircleaner box and plugging the opening with a snack container then feeding in air through the reference line of the bpv, with an air compressor. Low pressure like 5-10 psi.

 

What is the reference line? Is that a port on the bpv or is it a hose? Which port or hose is it? Thanks

[cww516]

There's a small vacuum line running to a nipple on the bypass valve, that's the one he's talking about using. That line snakes its way around the engine and into a port on the back of the intake manifold- air in that line will either close (under manifold boost) or open (under manifold vacuum) the BPV, hence the name. It's a convenient point to use for this test because you won't have air coming out of that port on the BPV when you pressurize that line, or at least you shouldn't. You'll be able to see it (more or less) under the car, but you'll be able to get a better grip on it from up top.

 

Take the passenger's side radiator fan out before you start yanking on that line, though, the skin on the back of your hand will thank you for it. Ask me how I know that one...

[ColbyMP]

There's a small vacuum line running to a nipple on the bypass valve, that's the one he's talking about using. That line snakes its way around the engine and into a port on the back of the intake manifold- air in that line will either close (under manifold boost) or open (under manifold vacuum) the BPV, hence the name. It's a convenient point to use for this test because you won't have air coming out of that port on the BPV when you pressurize that line, or at least you shouldn't. You'll be able to see it (more or less) under the car, but you'll be able to get a better grip on it from up top.

 

Take the passenger's side radiator fan out before you start yanking on that line, though, the skin on the back of your hand will thank you for it. Ask me how I know that one...

 

Thank you. That’s the one I figured he was referring to. I will surely check that out.