Boost leak - wastegate?

[iDub]

Did a bit more boost leak testing this morning, and seem to have found the problem. It seems to be the wastegate. If I pinch the hose going from the N75 to the wastegate it holds boost just fine. As soon as I let the hose go then the pressure drops right off. I've felt with my hand around the hose and can't feel any air, so it must be inside the wastegate itself.

I've yet to pull it apart, so what should I be looking for when I do?

[EspenW]

Air always leaks past the wastegate valve on these cars.

[Jamo]

Weak spring or split diaphragm, maybe also stuck piston?

You could try a a 1.9 spring in there ( give 0.9 bar wastegate boost )

[ranz]

Weak spring or split diaphragm, maybe also stuck piston?

You could try a a 1.9 spring in there ( give 0.9 bar wastegate boost )

The spring has nothing to do with it. Is the wastegate open or closed, the air shold not pass throw it anyway, but thats ideal condition Most of the cars usually have small air leak at wastegate valve "leg" whitch has been worn-out of moving up and down. I changed my cars wastgate and took it apart and that valve leg was the problem, but the new (used one) was not air leak free also, but it leaked a lot less then the old one.
But yes, it could also be broken diaphram.

[Jamo]

So the spring doesn't affect if the WG opens or not is what you are saying? I'll leave it there

If he blocks boost and the WG stays shut but then when it sees boost it can't hold boost pressure of course it could be spring related!

[ranz]

So the spring doesn't affect if the WG opens or not is what you are saying? I'll leave it there

Can you explain me how does open or shut down wastegate change the air flow from wastegate lower chamber to the exhaust?
I can answer it myself... it doesn't so... it does not matter what spring you have there.

[newsh]

The only way out from chamber below the diaphagm, where the pipe from the WGFV connects to, is down through the valve guide, this is often worn but pressure in real life is actually balanced somewhat by the exhaust pressure at the other end of the guide so is not normally considered to be too much of a problem. On old urs I have seen the chamber rotted through but this was because on early cars the WG was connected to the EM and opened by the exhaust pressure Of course if the WG diaphagm is split then the pressure will escape into the top chamber and exit through that little brass tube.

[ranz]

but pressure in real life is actually balanced somewhat by the exhaust pressure at the other end of the guide so is not normally considered to be too much of a problem

Thats right, considering that wiht original setup the exhaust pressure is usually doulbe of intake pressure, that leak is no problem at all.

[EspenW]

Test the diapraghm by connecting a small hose to the nipple and check if it holds vacuum.

[Rocco]

Test the diapraghm by connecting a small hose to the nipple and check if it holds vacuum.

or... use your tongue as me

[iDub]

Cheers for the input guys. I've not got any vacuum kit (other than a dyson) so I'll try the suck test!

I'll also pull the cap off and have a nose.

[EspenW]

Yep, no need for a vacuum kit, just suck on that nipple

[valjo]

Air always leaks past the wastegate valve on these cars.

are that 100% sure ? i have now 3 open wastegates on my desk and all have small leak via wastgate valve.
so that is ok ?

[EspenW]

Yep, the valve guide is not 100% airtight, and pressure in the exhaust manifold will balance it anyway

[S2central.net]

Totally agreed - have had numerous WG on the bench - they are far from airtight... it has always irked me, but as stated already its not really a big problem.

A leaky diaphragm is a different matter - that MUST be airtight so that pressure in the lower chamber cannot leak into the upper chamber. The 'suck test' is a good trick there.