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Can anyone tell me if having a boost leak will always cause turbo damage?

Ever since having the turbos replaced with refurbed K04's (in an S4) I've been suffering from leaks of one sort or another. Hopefully about to get the final ones sorted out when the one-way valves are replaced.

I must have done 1,000 miles since having the turbos fitted. For a few hundred of those miles I've had the N75 disconnected to prevent further damage and been driving like an undertaker, but it still makes a nasty wooo ghost noise (we need a ghost emoticon!) when spooling, even below 2k revs. It's particularly noticeable when the engine is cold (at this point I should also note that there is a very slight leak from an oil line connecting to the bottom of the noisy turbo). For the rest of the time I was under the (false) impression that the car was 100% and from time to time gave it some beans (as you would if you'd paid 1/6th of your house price for a 400bhp car).

When the N75 was connected up and the car was boosting it made a worrying noise at full boost, mostly from the passenger side turbo.
You could hear it spooling, then once at full boost it sounded like it was struggling to keep up the same flow and the 'whistling noise' fluctuated.

What sort of damage is caused by boost leaks?

What causes the wooo noise?

Does it sound like I need to replace these newly refurbed turbos or is it possible that they may have managed to escape any permanent damage?

Any help would be appreciated as i'm completely at the end of my tether now.

Sorry to hear of your woes - hopefully they'll be sorted soon and you can start to enjoy the car properly. I had boost leaks from time to time which sent the car into limp home mode which therefore protected the turbos. Iirc the vagcom fault codes thrown were "turbo over pressure" (but I could be wrong here). I did have a turbo failure (caused by poor lubrication to one bearing) and both units were replaced under warranty (phew) by a dealership. They didn't re-assemble it properly and you could hear the air pressure escaping whilst driving...I took the car back and they said it was normal (do you believe that?). Anyway, I protested and it was rectiified and despite the several hundred miles put on it at that time, the turbos are still fine (some 42,000 miles later)

Sorry long story that one!

The ghost noise should just be the turbines spooling up - they rev at something like 100,000 rpm (?? correct me if I'm wrong please) so are bound to make the sort of noise you report - listen to jet engines (forget the combustion roar and listen to the turbine whine..especially when they are starting up).

Keep us all posted?

HTH
Paul

I hear a hissing noise after the car is turned off and a boost pressure test always seems to show a slight leak at the back of the engine. However, I pressurisd the intake with the tester to 24PSI and the test "blew" off, sounded like a bomb. This showed however that despite hearing a leak, its clearly not big enough to vent that much air. The car is boosting to 28PSI (if I push it) and has never shown an error code.

Ill try again this weekend to find this mystery leak.
Incidentially my K04s have always made a wushy noise when spooling and considered it normal. Any and all engine noises sound louder when cold, wouldnt worry about that! You may want to post in the B5 S4 forum however.

This is what I think - I may be wrong.

AFAIK there are basically three main types of turbo failure - overspin, overheat and bearing failure - although all have the same 'ultimate' failure, being damage to the turbine blades (which is the worst case scenario when bits can come off and damage cats or engine internals). Boost leaks are the big risk of overspin. These cars have a closed control loop using the MAP sensor and the N75. AFAIK the ECU can't really detect air leaks unless they are major, so all that happens is that the turbos need to flow more air to meet the boost demand whilst air is being lost. If this happens at full throttle then the turbines end up spinning much faster then they were designed to and the turbines blades stretch. When the turbine blades have stretched the aerodynamics have changed and one of the results is the noise. If the noise is metallic then it means that the tips are scraping the housing (which can also occur with bearing failure).

In all my time reading forums about the S4, it is clear to me that healthy turbos do not make significant noise, and those which start to make noise are on the way out. The only exception is temporary noise, typically only when cold, which I guess is just caused by the exhaust before it expands.

Dippy - could you just clarify what you mean by "significant noise" - are you referring to the metallic noise you mention above?

I think everyone with K03s experiences the "whistle" to one degree or another. Mine have whistled since I bought the car at 24k miles, and the only difference 40k miles on is a slightly louder whistle/whine, which I put down to a change in exhaust. No change in boost levels (well not since MRC did their little magic 2 years ago )

Dippy, You mention that the blades stretching alter the aerodynamics. What i'm keen to know is, is this deformation permanent or will the blades return to their natural shape (if they haven't hit the casing)?

I think you'll find they are OK unless contact was made.

Dippy is just the odd one out. You gotta have some woo

Don't let the woo make you got to the loo!

Sounds normal to me, other than your known leaks. Keep driving like a Granny until they are sorted. A large enough leak will trigger limp mode and you will get the DTC 'Charge Pressure Exceeded'. I love the WOOOOOOOOOOO sound - like a 747 taxing at Heathrow - the neighbour always looks up into the air.

Woooooo...

I hear a hissing noise after the car is turned off and a boost pressure test always seems to show a slight leak at the back of the engine. However, I pressurisd the intake with the tester to 24PSI and the test "blew" off, sounded like a bomb. This showed however that despite hearing a leak, its clearly not big enough to vent that much air. The car is boosting to 28PSI (if I push it) and has never shown an error code.

You should only pressure test to 15PSI max IMHO!

What setup have you got to run a peak boost of 28PSI??? That's ridiculously high for K04's.

I am sure I have read pressure testing at too high a pressure actually damages seals and does more harm than good. Be careful.

Whoooooo ghost noise generally means that you have lost a blade from the hot side of the turbo.

This in turn means that the turbo is now un-balanced and will result in the bearing going at some point and the turbines embedding themselves into the casing of the turbo... possibly shattering causing even more trouble.

Sounds like another engine out job to me unfortunately mate

or you mite be lucky enough to have a faulty wastegate and its stuck open in some way...