hissing/boost problem

[hermanio]

my urs4 developed a problem today.
under boost i can hear a very loud hissing sound comming from the engine bay/passenger footwell.the car doesnt feel as quick as normal. i dont get a fuel cut under boost.

what i allready checked:
- replaced the vacuum/boost hose between the intake manifold and ECU for a new one
- Did a pressure test and all the hoses seem to hold pressure (all my boost hoses are silicon)
- checked N75 valve, no leaks- checked hose between n75 and waste gate
- tested wastegate diagram, seem to hold vacuum
-checked the one way valve under the intake manifold
-checked connections at moisture trap.
-checked the hose inside the ecu.

also with a pressure test i cant reproduce the sound. Normally with a boost leak you get a fuel cut but i didnt get it this time. Should that mean thats it on the exhaust side ?

any clues ?

[Lloyd]

edit, re-read OP. Hmm not sure?

[Avantus]

blown mani gasket?

[hermanio]

I think i found it, just checked the exhaust manifold and found 1 loose nut. I tryed to tighten it but i was allready broken. What is the best way to replace the stud ?

[Greg_S]

Remove the exhaust manifold, and hope there is enough of the thread sticking out to remove the stud after giving it a good soaking with WD or similar. If that doesnt work likely a head off and off to a machine shop to have it sorted out,

[4WheelDrifter]

That has snapped off inside the head I am afraid. You will either have to take the head off to extract it, or try to drill it out in situ.
I have done this in the past by making a plate that can be bolted to the exhaust port, with a perpendicular tube attached to hold a drill bit straight, and in position to drill the centre of the offending stud. You will probably need a 90° drill too.
It looks like the stud has snapped off fairly squarely, which helps.

When you have drilled a good sized hole into the stud, you can either use a reverse drill bit, or smack a spline or torx bit into the hole to wind the stud out. Use the biggest bit you dare, without drilling the actual head.

Good luck.

[rynaqui]

A risky job though..I think a head off job to be safe..

[4WheelDrifter]

Either way it's not an easy job. The head off could be more time consuming, but much easier. If you **** up the in situ job, the head will have to come off anyway.