# Buzz/Exhaust Leak sound after downpipe install. SAI system?



## Chatchie (Aug 9, 2014)

Hey guys.

Few weeks ago I installed my catless non resonated downpipe. 

I used a new OEM DP gasket and a new 60mm exhaust coupler for the rear section.

Right after installing it sounded like I had an exhaust leak so I figured it was the cheap V band since it was a Godspeed downpipe. It wasnt. I tripled checked everything and all was tight so I brought it to my local custom exhaust shop for them to look at it. 

They say it was my brand new $50 rear coupler so they chuck that and weld that joint up. I wasn't really happy about that but whatever, they say the exhaust is all tight. I pick the car up and I still have what sounds like an exhaust manifold leak only under load. It's a buzzing farting sound.

I then tried stuffing rags in the tips to isolate the leak and find nothing, the exhaust does indeed does seem tight.

I then had my wife drive the car by me full throttle and I don't hear the leak. It seems like it's only audible while in the car. I had her drive by me back an forth untill she got pissed off and said I have OCD and there is no sound.

Here's the thing, I've noticed on cold starts the car sounds like it has a viscous exhaust leak then goes silent after a few seconds like something is up with the Secondary Air Injection system. 

Is the SAI system tied to the exhaust in any way?

Would a knocked loose hose cause a sound like this?

Does anyone have diagrams if this system?

Could it be just be a normal sound from my thin walled down pipe?

This morning I got a code for improper flow of SAI system P0491 which illuminated the light bulb in my head.

Thanks so much guys. 

2010 cbfa with carbonio 1+2 and stock catback

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## Chatchie (Aug 9, 2014)

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## The1Bill (Dec 8, 2009)

I think that there are two discrete issues here; first, you have a buzzing exhaust leak sound under load that started after you installed the downpipe, and second, there is a lot of noise after a cold start.

For the second noise, SAI pumps fresh air into your exhaust for the first few (~30?) seconds after a cold start. I don't know how the Carbonio accommodates SAI, but my Unitronic intake has a small separate filter for the small accordion pipe that runs to the SAI pump.

My open element baby filter for SAI is *LOUD* when SAI is active. With the hood open, a loud sucking sound is obvious from the little filter, and it does sound a bit like a exhaust leak (or a jet engine!) until the cycle concludes.

Back to the first sound, though, the exhaust leak sound. Could the downpipe be touching anything and transferring vibration when the engine rocks? Your comment that you notice the buzz under load would support this theory.

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## Chatchie (Aug 9, 2014)

I've through about it being a vibration but the only thing that has interference is the carbonio stage 2 rubbing on the brake booster and Ive had that on for a while before the Downpipe. 

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## The1Bill (Dec 8, 2009)

Chatchie said:


> I've through about it being a vibration but the only thing that has interference is the carbonio stage 2 rubbing on the brake booster and Ive had that on for a while before the Downpipe.
> 
> Sent from my XT1575 using Tapatalk


I had to clearance the heat shielding slightly when I installed my USP downpipe. Yours may fit differently, though. Besides, I'm not sure that the heat shield could produce a vibration.

Are the O2 sensors all happy and tight?

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## Chatchie (Aug 9, 2014)

The1Bill said:


> Are the O2 sensors all happy and tight?
> 
> Sent from my XT1096 using Tapatalk


I've tripled checked everything. I was even wondering if the flex section had a tear causing a leak under load but theres no carbon "stains" anywhere.

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## The1Bill (Dec 8, 2009)

Chatchie said:


> I've tripled checked everything. I was even wondering if the flex section had a tear causing a leak under load but theres no carbon "stains" anywhere.
> 
> Sent from my XT1575 using Tapatalk


Well, perhaps it is the pipe itself, as you posit. I'm out of ideas otherwise. If it is the pipe itself, a bit of thermal wrap might be what the doctor ordered.

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## snobrdrdan (Sep 10, 2008)

Could just be the exhaust noise you're hearing now.

Without the restrictive cats quieting the exhaust anymore (especially the one right after the turbo & right in front of the firewall), you're hearing the exhaust rushing out of the turbo now inside the cabin.

Don't worry, I freaked out too on my MK5 GTI when I put a downpipe on the first time thinking the same thing


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## Chatchie (Aug 9, 2014)

Yea it very well may be. I'm sure I defiantly have something going on with the SAI system as I get a code on every cold start now.

It actually snowed today and I won't have access to a lift untill this weekend so ill post back with my findings. Ill get a video up later this afternoon once the snow melts.

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## Chatchie (Aug 9, 2014)

snobrdrdan said:


> Could just be the exhaust noise you're hearing now.
> 
> Without the restrictive cats quieting the exhaust anymore (especially the one right after the turbo & right in front of the firewall), you're hearing the exhaust rushing out of the turbo now inside the cabin.
> 
> Don't worry, I freaked out too on my MK5 GTI when I put a downpipe on the first time thinking the same thing


I think your right. I took my intake off and put the stock air box on so I could hear better.

The "sound" is still there but much quieter. What I'm hearing is the exhaust rushing through the thin walled downpipe.

Tell you what, I like my car better now without the intake. Thing makes all kinds of friggin noise with it on.

On to the next problem with my SAI. The car has been sitting for 3 days so I jacked it up to take a closer listen to the pump on cold start. I start it and the SAI doesn't engage. No check engine, nothing. Just runs perfect. I don't get it, the car was covered in snow, it should have gone through that cycle.

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## snobrdrdan (Sep 10, 2008)

That's good

As for the SAI, it should run everytime on startup for like 10-20 seconds....not just if it's cold.
You would have heard it more with the aftermarket intake though...it's quieter going thru the OEM airbox, FWIW


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