Hissing or Hi-pitched rattle under acceleration - Subaru WRX Forum
 
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post #1 of 14 Old 04-10-2006, 02:07 PM Thread Starter
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Exclamation Hissing or Hi-pitched rattle under acceleration

Hey there! thanks for checking to see if you can help. This is driving me nuts.

I just put on Helix Up and Down pipes, Borla Hush muffler and a Perrin Crank Pulley.

After the install, I get a hissing sound from the engine compartment. It happens when the RPMs are 4,000+ and accelerating. If there is no load, there's no sound. It is pretty loud.

The sound could also be a high pitched rattle that "ticks" really fast..

My first thought was exhaust leak but I don't think you'd hear it that much.. The shop put it up on the rack to see if there were dark areas that would indicate exhaust leak and we didn't see any...

I'm wondering, do you think that a vacuum hose or something was not properly reconnected after the install?


The guy at the shop said I could schedule time to bring it in again, but I need to know where to point him..

He said.. "seems kind of normal to me. I think you are just hearing your wastegate"

But this is when it's under load. and I NEVER hear it when I push it hard then get off the gas quick..

any help is MUCH appreciated!

Thanks!

Joel
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post #2 of 14 Old 04-10-2006, 04:55 PM
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Well doesn't sound a waste gate to me...possiblily your belt on the new pulley making all that noise...A vaccum leak would be heard all the time not just when the motor is under load..if you had a shop install your parts I would hold them responsible for finding the problem

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post #3 of 14 Old 04-10-2006, 06:11 PM Thread Starter
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Thanks for your thoughts Nick

Perhaps I should have the shop switch back to the stock pulley (since it's quick and easy) just to see if that takes care of the issue. Or do you think it would be easier just to drop on a new belt? Would be fast and pretty cheap...

either way, it's a lot easier than trying to rip apart the up/ down pipe to see if there is a leak..

Would you hear the hissing of an exhaust leak anyway? if is is a leak, I would think that it would have to be where the turbo attaches to the Up Pipe since that is the location with the greatest amount of pressure (or other end of up-pipe).. still, could that be heard?? It seems like a lot of noise for what would be a small leak.

I really appreciate your help.

Joel
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post #4 of 14 Old 04-10-2006, 06:50 PM
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I would say it is an exhaust leak mainly becuase you hear it after the turbo is fully spooled, therefore moving more air through the exhaust. The pulley could be eliminated just by inspecting the belt, if it is frayed then something is messed up when they installed teh pulley. The leak might just be they didnt tighten up the bolts/nuts enough when it was installed.

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post #5 of 14 Old 04-10-2006, 07:08 PM Thread Starter
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Thanks Jave! That totally makes sense too!

I saw a post where someone recommended having a friend put a shoe covering the exhaust tip.. then rev the engine.. That would create a lot of pressure so you could hear it without trying to climb under the hood at 50MPH..

I could test this way myself without having to wait till the weekend when I can get it down to the shop.

These are both great recommendations. Thanks so much Jave and Nick. I'll let you know how it goes.

Best,

Joel
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post #6 of 14 Old 04-10-2006, 07:35 PM
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Quote:
Originally Posted by shrockie
Thanks for your thoughts Nick

Perhaps I should have the shop switch back to the stock pulley (since it's quick and easy) just to see if that takes care of the issue. Or do you think it would be easier just to drop on a new belt? Would be fast and pretty cheap...

either way, it's a lot easier than trying to rip apart the up/ down pipe to see if there is a leak..

Would you hear the hissing of an exhaust leak anyway? if is is a leak, I would think that it would have to be where the turbo attaches to the Up Pipe since that is the location with the greatest amount of pressure (or other end of up-pipe).. still, could that be heard?? It seems like a lot of noise for what would be a small leak.

I really appreciate your help.

Joel

An exhaust leak under the hood is very obvious...you can hear it puff along with your idle....if you really think it is an exhaust leak put some seafoam through the vacuum hose that goes from the master cylinder to the block...the leak will smoke a lot...and if there is no leak than your exhaust will smoke...this will show you where any leaks are at the same time cleaning some carbon for your internals

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post #7 of 14 Old 04-10-2006, 10:45 PM
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This is my opinion... I have been chasing a sound exactly like what you describe for 8 months now. It happened after i installed helix UP and DP. The shop i had my car tuned at didn't think it was a problem. I used copper gaskets and copper sealant on all my exhaust connections. I checked for exhaust leaks and there are none. I replaced the BOV thinking it was compressor surge. I am sure its just the waste gate now. I have adjusted mine but it didn't help. Don't waste too much time on this sound. If your car performs well then leave it be. It takes a lot of time to try and fix this sound.

Jacob
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post #8 of 14 Old 04-11-2006, 06:20 PM Thread Starter
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Hey Jacob, Thanks for your thoughts.

As I understand it, the wastegate is supposed to operate when there is excess pressure in the system. Like when you are revving hard and then get off the gas..

I'm finding that my noise is audible when I'm at 3,800+rpms and climbing.. If I let off the gas, the sound goes away. My sound is very tied to load and RPMs. Do you think the wastegate would operate under these conditions?

Does your noise become active in the same situation? But disappear when you are off the gas?



What kind of UP/ DP did you put in? (mine is Helix for both.)

Sorry to hear that you've been trying to find the same thing! Thanks again for your input.

Best,

Joel
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post #9 of 14 Old 04-11-2006, 06:23 PM
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Quote:
Originally Posted by shrockie
Hey Jacob, Thanks for your thoughts.

As I understand it, the wastegate is supposed to operate when there is excess pressure in the system. Like when you are revving hard and then get off the gas..

I'm finding that my noise is audible when I'm at 3,800+rpms and climbing.. If I let off the gas, the sound goes away. My sound is very tied to load and RPMs. Do you think the wastegate would operate under these conditions?

Does your noise become active in the same situation? But disappear when you are off the gas?



What kind of UP/ DP did you put in? (mine is Helix for both.)

Sorry to hear that you've been trying to find the same thing! Thanks again for your input.

Best,

Joel
Yours sounds like the belt/pulley to me

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post #10 of 14 Old 04-11-2006, 08:07 PM
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one thing just hit me about this, are you running catless DP? It might be the turbo noise you get with a freer flowing exhaust. Is there any shops in your area that has experience with a WRX? If so, you might drop by there and see if they could go for a short test drive iwth you to listen to it.

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post #11 of 14 Old 04-11-2006, 09:04 PM Thread Starter
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Hey There,

I just found a nice little doc on how to mellow out the ticking sound.. It really seems like it could be wastegate flutter.. I just gave it a test and it seems to be working a little. Only took about 15 mins. and a 10mm wrench.

they advise 3 turns. I think I only did 2 to play it safe. I'm going to hook up my boost guage (access port) to make sure I'm still safe then give it another turn or so.. Just easing into it.. I'll let you know if turning further helps more. I'll get back to you tomorrow.

http://www.scoobymods.com/forums/arc...hp/t-3654.html

photo:
http://cakonos.image.pbase.com/image/22312910.jpg

Hope this is helpful!

cheers,

Joel
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post #12 of 14 Old 04-11-2006, 11:16 PM
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that was going to be the next thing I was going to suggest. But good to hear you found what might be the issue.

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post #13 of 14 Old 04-12-2006, 02:12 AM
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Awesome....Glad to hear things work out for you the easy way

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post #14 of 14 Old 04-12-2006, 06:22 PM Thread Starter
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Many thanks to Nick, Jave and Jacob for their help with this!

I'm chalking up the sound to be wastegate flutter. When the Up and Down Pipes + Exhaust were put in, it caused two things..

1) There is less back pressure on the wastegate because of high flow down pipe and exhaust system. This means there is not as much pressure on the back side of the wastegate holding it closed.

2) A catless up pipe allows for the bursts of air to go straight to the wastegate instead of being slowed down (and evened out) by the Cat in the up pipe. These burst of exhaust cause it to open slightly and generate a "ticking" sound that is in time with the engine.

The Solution: I adjusted the wastegate actuator arm and preloaded the spring in it slightly. (See posting above) Be careful not to over shorten the actuator arm, it still needs to function to protect your engine. Check your boost levels to make sure you did not over tighten. Your boost level may spike early if it's too tight. The noise is softer now, but still present. I'm happy that this was able to make it quieter though!

Best of luck to any one else that's having this issue. I hope this info is helpful.

Cheers,

Joel
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