cobalt

So I have isolated this high frequency shrill noise coming from my car. Thought it was a flange now I find out it is not. It is coming from the pipe that runs from the aux air pump that usually feeds into the cat just next to the muffler and support strap.

I have an aftermarket exhaust and the cat has been removed for a long time. This just started within the past few miles and I have been avoiding driving the car until I could figure out where the noise is coming from. I have done my research and even fabspeed show this left open as it is on my car. So why all of a sudden am I getting this noise?I have no idea why it comes and goes and it is apparent between 2700 and 3400 rpms with it being loudest at 3k.

I am assuming capping this off would not be a smart idea since there is no place for the air to go.

Anyone have a similar issue? I am assuming it is the check valve number 9 shown on the PET. Possibly stuck in the open position or the valve is vibrating at those RPMS. There is a huge amount of hot air that flows through it even when engine is cold. If anyone has a fix please let me know other wise I will start buying and replacing parts.

Metal Guru

As I recall, air is injected into the exhaust ports during warm-up and then into the cat when the engine reaches temperature.
A whistling sound is indicative of a restriction.
I would bet the valve is stuck in a partially closed position.
I'd start by inspecting that valve.

cobalt

Definitely stuck someway or another. There is a lot of air flow coming out of it even when cold so I am assuming possibly stuck partially open. (Half full LOL)

It is a simple fix that takes hours unfortunately. Difficult to access since it is just below the A/C bracket. Might be easier to remove the lower tin to access.

Metal Guru

Yes, I'd remove the lower tin. Going up top is a considerably bigger job.

cobalt

Talk about driving you crazy.

I looked it over and found if I remove # 7 connection piece and the clamp going into the diverter valve #1 the hose and check valve came out easily. I did have to remove the top section of the heater hose by the oil filler as well to do this.

Check valve is not the issue it seems to be a simple device which compressed air only flows in one direction.

I ran the car with the hose off the diverter valve which flows air and no sound. I connected the hose back and left the check valve hanging loose again no sound.
Connected the connection piece to the check valve and let it hang loose and no sound. I replaced the check valve and connection piece to the engine tin and the sound is back. Although now the sound is between 3000 and 4000 rpms vs 2700 and 3400.

I must conclude that the sound is a resonance or vibration of something touching the engine tin? Problem is I can't find anything.

I am seriously thinking of either capping off the end of the connection piece or disconnecting it from the air pump but would prefer to have the parts in place.

Sometimes

Metal Guru

There's supposed to be a grommet around the #7 union. Is it there or has it perished.
If it's a vibration all you can do at this point is lock everything down and cushion any metal on metal interfaces.

cobalt

Yes there were actually two one on either side of the engine tin.

What I don't get is the car has been this way for so long and now it started making this noise and it isn't consistent. I will play around some more and see if anything changes.

cobalt

Replaced the aluminum sealing ring with a rubber O ring and it seems to be all better. Still not sure why this would have become a problem after all these years but so long as i can safely drive the car I guess I don't care.

Metal Guru

Good news....

RR

I have 91 Turbo with 40,000 miles with a fab speed exhaust and I have had the similar issue intermittently, but mine occurs only just after start up and moves up and down with the throttle but only lasts 10-15 seconds.
At first I thought it was the starter making this squeaking noise but it can't be if it is moving up and down with throttle, or could it?

cobalt

Assuming it is the same sound mine was definitely coming from the air port located in the picture above.

I do find it strange that it began after all these years for no apparent reason. I placed my finger over the outlet from the diverter valve inside the engine bay when i disconnected the hose. It would appear that plugging it wouldn't make a difference since I was able to keep my finger in place while my friend revved the engine. I decided not to chance it. I might be putting my original exhaust back in the near future anyhow.

I don't see Fabspeed or any other aftermarket exhaust company offering a cap or advising on capping it in their instructions.

Metal Guru

I don't think you want to cap that.
It's essentially connected to a compressor, which is being driven by the engine. You can imagine where I'm going with this...
I'd leave it open to the atmosphere.

cobalt

My thought as well. I am surprised that here aren't more having this problem. maybe I should check the 930 forum to see if there are more instances since they use the same exhaust.

Metal Guru

What I noticed when I first bought my car was that the air header was rusted through due to condensation inside of it. Seeing as I wanted a German hot rod and don't car for nut and bolt originality, I scrapped the entire system. The idea of -10 lbs and better access to the engine was irresistible. If I owned a 3.6, then it would have been a different story altogether.

RR

Hi

Tried uploading a vid of my squeak but file was too large.

I have a 91 964 Turbo with 40,000 miles - 2500 miles on the engine reseal and at the time of engine reseal my mechanic installed a fabspeed exhaust.
This clip shows the annoying squeak I get when I start the car.
Squeak goes away once warmed up but my mechanic says that there is nothing I can do about it bc it is just an expansion joint in the exhaust that needs to be there.
The car just started squeaking last summer at start up.
I had approximately 1500 miles squeak free.
Does anyone else have this issue with their fabspeed exhaust on their 965?
The noise is really annoying.
Any help is appreciated.