Wastegate air leaking into exhaust

[dkw_dude]

Efi Express is advertising rebuilt KKK wastegates, have anyone tried them? My WG has a very roomy valve guide so I'm considering buying one!

http://www.efiexpress.com/catalog/product_info.php?name=rebuilt%20KKK%20wastegate%20assembly&products_id=56

I think there's a 30mm (older 10VT engines) version of the WG, on the 20VT the WG should be 35mm, worth checking whick version you have before buying.

[s2_wot]

Interesting vídeo Ian, thanks for posting. I must test my own one of these.

[Lloyd]

Got my wastegate reconditioned by Rich aka (Hoffer76).

Terrific job, looks brand spanking new and works a treat.
My old WG was definitely leaking air, mostly due to a tired original spring.

Here's a shot of the new one:

[prj]

My old WG was definitely leaking air, mostly due to a tired original spring.

No, that's not why it was leaking air at all. Also, the "tiring spring" is pretty much a myth.
The spring has nothing to do with it leaking air...

The wastegate looks mint on the outside though.

[Lloyd]

OK, what's your thinking then?

[prj]

OK, what's your thinking then?

One leak is between the lower and the upper chamber due to the diaphragm not sealing well, other one is between the exhaust side and the lower chamber.

Neither of them will be caused by the spring...

[Lloyd]

The diaphragm was and still in good condition - no leaks - easily tested on anyone's WG by attaching a pipe + vacuum pump to the upper WG port.

I think this WG was previously leaking or bleeding air past the piston due to the tired original spring, which was allowing the piston to open sooner that it should, delaying onset of full boost.

[ian4455]

What causes the "Fluttering" noise under hard driving, informed this has something to do with wastegate ?????

Nice job done on the wastegate !

[prj]

What causes the "Fluttering" noise under hard driving, informed this has something to do with wastegate ?????

Nice job done on the wastegate !

Either diaphragm is toasted or if it is when you let off, the dump valve.

The diaphragm was and still in good condition - no leaks - easily tested on anyone's WG by attaching a pipe + vacuum pump to the upper WG port.

I think this WG was previously leaking or bleeding air past the piston due to the tired original spring, which was allowing the piston to open sooner that it should, delaying onset of full boost.

You got it wrong here and I will explain why. I already did once, but it seems that I need to do it more precisely.

For that one needs to look at Audi's N75 topology.
The N75 has a restrictor in the middle port, which points towards the turbo.
That restrictor is there so too much air does not go through the boost control system, in fact the amount of air is miniscule that passes through there in the grand scheme of things.
So your assumption, that you have a boost leak in the wastegate and that it is somehow affecting your car is completely wrong.

Now let's go to the wastegate diaphragm. If that is broken, then your car will boost more, rather than less.
This is because the pressure that is going to the lower chamber and is supposed to work against the spring is escaping. Ever seen what happens if you disconnect the lower port? The same thing is happening when the diaphragm is broken.

The issue with the wastegate tends not to be the spring, but rather that it is possibly not sealing properly anymore, being effectively part-open all the time and bypassing exhaust gases even when not needed.
The "tired spring" myth is usually invented as an excuse because people can not find a blatantly obvious air leak or some other thing wrong with their car. They wind down the spring, and the car makes a bit more boost for just a moment, so they think it is the spring.

It is easy to jump to false conclusions when the base for your assumption is wrong.

[driftin jo]

They leak air past the valve guide/bush when it is worn badly, they all leak a bit past even when new but this progressively gets more and more with wear. The other type of leak is as PRJ says , past the diaphragm (giving increased / overboost).
An bad air leak past the bush give you sluggish boost response in operation as exhaust gas goes past it and helps open the gate early/more. (I'm sure I've said this before)

[prj]

[Lloyd]

You got it wrong here and I will explain why. I already did once, but it seems that I need to do it more precisely.

The issue with the wastegate tends not to be the spring, but rather that it is possibly not sealing properly anymore, being effectively part-open all the time and bypassing exhaust gases even when not needed.

It is easy to jump to false conclusions when the base for your assumption is wrong.

Charmed.

You're saying the same thing as I - not sealing properly = bleeding past air.
Air can leak/bleed past due to wear and also due to shagged spring. Both checked out at service and working nice now.

[prj]

Charmed.

You're saying the same thing as I - not sealing properly = bleeding past air.
Air can leak/bleed past due to wear and also due to shagged spring. Both checked out at service and working nice now.

I would not call exhaust gas air, and I have not seen any of the springs go bad.
But whatever.

[Lloyd]

You know what I mean

[prj]

You know what I mean

I did not at start, but now I see that we did mean the same thing.