Boost Leak

[chook]

Just got back from my 3000k road trip, Stag performed fine, got 10.5L/100km (9.5km/L), which i was happy with.

However, during the trip the intake developed a leak i think, idling fine but will no longer reach desired boost, about 0.05 bar below, and has a low pitch whistle sound above 0.5 bar, not there before and separate from the usual spooling sound. Done a quick check of hoses, and now thinking it may be around the turbo itself.

Anyone have any ideas on the most likely place for a leak on the turbo ? seals. gaskets etc

PS sydney drivers, the horn is not a blinker.

[116.hks]

hey mate. If you had a leak after the AFM, you notice the car will idle rough. Check to make sure you have no shaft play in the turbo. Thats the only thing that will make a high pitch noise under boost and possible lose of boost.

[chook]

thanks, seems to be a leak which only forces itself out under some pressure. Will try blocking off the hoses at each end and pressurising the system to see if it shows itself.

[lachlanw]

check your exhaust manifold and the gaskets . and dump pipe . youd be surprised at all the noises that can be linked back to this

[chook]

update; pressure tested the intake system, held fine. No visible/audible exhaust leaks, but really need a dyno to check properly.

tested the PCV valve, faulty, should be a one-way valve, its leaking boost air into the crankcase from the intake manifold.

Not sure if this is the smoking gun im looking for but i wont go any further till I replace it.

[66yostagea]

update; pressure tested the intake system, held fine. No visible/audible exhaust leaks, but really need a dyno to check properly.

tested the PCV valve, faulty, should be a one-way valve, its leaking boost air into the crankcase from the intake manifold.

Not sure if this is the smoking gun im looking for but i wont go any further till I replace it.

I just went thru all this, or similar. While fitting the R34 smic I broke the seal on the intake hose to the turbo. Sounded like a CA spooling up. There is a thread on it. Even bought another turbo caus I thought mine was RS. I also found three leaks in the exhaust mannifold because of broken studs and a huge crack in the manni where the turbo bolts on. It was a long and frustrating experience as Mrs could not drive the manual Skys.

But now she runs like a Nissan.

[DaveB]

Interesting point about the PCV valve. I was just thinking though that perhaps that is a bit backwards... I could be completely off here (someone please correct me?) but I think the PCV valve connection is to the intake side of the turbo, so the one-way valve is purely to prevent the manifold sucking air in under vacuum? I didn't think it had a connection to the boost side of the turbo? If it does then I don't trust mine either as it doesn't make a perfect one-way seal (but then no PCV valve I've ever played with ever has).

Edited December 24, 2008 by DaveB

[chook]

It is designed to suck air from the engine into the intake manifold under vacuum, and seal off under boost. I have cleaned out the carbon deposits in mine and it is still not a completely tight seal. Has anyone played with a brand new one ? Are they supposed to be air tight ?

Interesting point about the PCV valve. I was just thinking though that perhaps that is a bit backwards... I could be completely off here (someone please correct me?) but I think the PCV valve connection is to the intake side of the turbo, so the one-way valve is purely to prevent the manifold sucking air in under vacuum? I didn't think it had a connection to the boost side of the turbo? If it does then I don't trust mine either as it doesn't make a perfect one-way seal (but then no PCV valve I've ever played with ever has).

[donut_kng]

+ 1 for broken exhaust manifold studs RB's come factory with this had VL's and liners with it.

Also shit the turbo gasket which is how i noticed the studs, this made it sound like I had some birds nested in my engine bay.

[kidafa]

update; pressure tested the intake system, held fine. No visible/audible exhaust leaks, but really need a dyno to check properly.

tested the PCV valve, faulty, should be a one-way valve, its leaking boost air into the crankcase from the intake manifold.

Not sure if this is the smoking gun im looking for but i wont go any further till I replace it.

And how did you pressure test the intake system?

[M I K E]

my money is on manifold to turbo gasket. if you've lost some boost pressure and are getting a whistling sound then i'd be checking the studs that hold the turbo to the manifold are done up tight

[chook]

And how did you pressure test the intake system?

real backyard stuff, blocked off the hose into the AFM (with a wine bottle), blocked off the reducer hose before the throttle (with a can of fly spray). clamped them up. Also clamped off a few other smaller hoses, pressurized the system with a bike pump. around 10psi, held fine, couldnt hear any leaks.

[chook]

my money is on manifold to turbo gasket. if you've lost some boost pressure and are getting a whistling sound then i'd be checking the studs that hold the turbo to the manifold are done up tight

thanks, will check this next, although might just give it to Godzilla motorsport for them to do.

[66yostagea]

my money is on manifold to turbo gasket. if you've lost some boost pressure and are getting a whistling sound then i'd be checking the studs that hold the turbo to the manifold are done up tight

When mine started sounding like a CA I went straight home and started stripping down caus I thought it was the turbo, which it wasn't.

It seems that there are many reasons to cause the "noise". My turbo to manni nuts were up tight but there was the crack right across the manni mounting

aperture, also the three leaks in the exhaust caus of broken studs. I came across the intake hose looseness on the way in but kept going to check the rear end of the turbo, which was fine. The stud problem needed fixing and was done. I am still not sure what was the exact cause and this still frustrates me.

[DaveB]

Well I'll be... the PCV valve does appear to connect to the inlet manifold/plenum!? So when you're boosting, and getting the most blow-by, the pressure on the other side of the PCV valve is your boost pressure which means that it's least capable of doing its job...???