HISS noise at high RPM

[Lawry]

Hey guys

having a small boost issue i think...
It happens right around 2700-2800
the sound is a loud hissing noise, much like the noise i think the butterfly makes at a certain RPM.

It never used to do this, I could pull past 3 thousand without this noise occurring.

I have pressure tested every inter-cooler section besides the EGR blocking plate which has a new cork gasket, looks to be sealing!

Could it be the EGR pipe? say a crack?

when the noise is present the boost will drop from 18 ish psi to around 16-17.
so it seems there is a boost leak somewhere.....
but confusingly enough im making boost earlier at around 2000 but no noise, its only when i get higher in the rpm range..........

is there a way i can test for a manifold leak?

 

[wunlowcourier]

Mine is doing the same thing mate. I don't have a boost gauge but i have an xr6 intercooler. It was doing it before i put the cooler on. I've got no idea what it was but its annoying. Mine starts at 3000 rpm. Would be good to know what it is

 

[4BYFOR]

Hey guys I would defiantly check all intercooler pipe work hoses and connections the only hissing noise that can be made in my opinion is when turbo spools up to required boost and there is a leak.. I have had this happen to me several times and its always been a connection because I have hard piping.. You may have a small hole in one of the hoses best you check it over before you move on to another issue. Also check your intercooler for cracks too! Good luck

 

[Rumpig]

Exhaust manifolds are know to warp and leak as well. There's also been some EGR pipes thet have cracked.

 

[Lawry]

thanks guys
ive checked boost leaks from turbo to inter-cooler (xr6 as well) to manifold and there where none...

naturally there was one fitting that wasen't test, as it was required for blocking of the system to be pressurized.
i have put two clamps of that hose to try and rule it out.

the only this else is the inlet manifold is leaking or EGR pipe but is the EGR pipe even under pressure???

any way of testing the inlet manifold for leaks, would it damage the engine if i pressurized from the turbo to the exhaust manifold???

 

[tweak'e]

yes egr pipe is under pressure. its higher than boost pressure.
mine cracked at exhaust manifold end and fell off ! big roar no boost !

unbolt the turbo covers and look for any soot.

 

[Lawry]

The heat shields are off and i cannot see any soot.
i have put some bolt release spray on the EGR fitting at the exhaust manifold and have got 2 out of the three bolts to loosen, will let the third soak over night.

I think tomorrow i will make up a stainless plate and block the EGR off at the manifold, its currently blocked at the other two regions on the inlet manifold side.

if worst came to the worst, how would i fix a inlet manifold leak.. say its warped any easy solution?

tweake, do you reckon the EGR could make a hiss noise?

 

[tweak'e]

yes the egr could make a hiss noise. they tend to crack at the weld.

 

[Lawry]

Removed the EGR pipe, looked fine, blocked it off and there not difference.
has to be on the inlet side....
a bit stumped.

 

[shane76]

I had a split in the intercooler pipe from the turbo to the top of intercooler.

 

[chule]

There's a thread somewhere on the forums about Allen bolts coming loose and falling out of the back(?) of the turbo which makes a hissing sound. Might be worthwhile checking out too.

Good luck.

 

[Lawry]

There's a thread somewhere on the forums about Allen bolts coming loose and falling out of the back(?) of the turbo which makes a hissing sound. Might be worthwhile checking out too.

Good luck.

I'll try that next, need to make another custom Allen key seem to have misplaced mine. Have also found an exhaust leak but way down system at the fuel tank. Exhaust wrapped it but yet to test. See I noticed this noise when I removed muffler, this leak is either from the exhaust leak found or the fact I'm developing 1psi more in boost from increase flow enough to create a leak. Time will tell

 

[Lawry]

tested allen key bolts, all tight... what next

 

[mooxie]

I'm keen to know how you go, I've got a similar problem, however I can hear the hiss from about 2,000 RPM on wards, when under load.
I've replaced the hoses, however found a small leak on the exhaust manifold - turbo gasket and also where I've blanked the EGR.
I gave up and took it to the mechanic. After two days, they can't pinpoint where the sound is coming from as it doesn't occur in neutral.
Think I might bite the bullet and buy all of the gaskets on the turbo and EGR and replace them! Can't think of anything else to do!

 

[Lawry]

well overall i found black oil residue on the back of one of the turbo bolts, not the allen key's but the outer bolts that crush the compressor manifold onto the turbo housing. It either isn't seated properly or the seal is a bit weak at that point. The other visible region was a corner of the inlet manifold i can see it but not sure if it worth chasing as i pressure tested just the turbo to 20psi and there wasn't any leaks so i don't think i would be any more successful if i removed the entire inlet manifold and fixed the gaskets. Im planning on putting a new turbo (high flowed) in the near future i will check the gaskets then but until now i cant be stuffed to be honest. You will end up chasing your tail.

see my problem is a combination of boost and revs I will be on boost 17-18psi at 2000 but it wont occur until 2600-2800 ish... got me stumped.

 

[mooxie]

I may have been lucky... but mine turned out to be the turbo intake hoses. I replaced the intake hoses and seemed to be no change. Found a couple leaks in the exhaust side of the turbo, put new gaskets on the EGR side of things, no luck. Couple days at the mechanic... no luck. (as it only happens when accelerating or under load, above 2000 rpm). For me, turned out the original sound was from a small perforation in the intake hoses. Replaced them and the 60mm top hose was slightly too long, which I didn't realise. Noticed everything looked a bit skewed, cut 1cm from the top hose and bam... noise gone. The new hoses were a bit skewed and one wasn't sealed 100% because of this!
Two tricks to try... spray soapy water on the exhaust side and look for bubbles... on the intake side, have someone rev the engine to 2000 rpm and hold it... spray aerostart on the intake hoses and gaskets and see if it surges on any!