[Biturbos4] Re: All causes to turbo failures known?

[Charles Wurts]

Great post Keman!  As always, thank you for your contributions.

Charlie



On May 10, 2004, at 4:03 PM, biturbos4-request at www.audifans.com wrote:

> Message: 4
> Date: Tue, 4 May 2004 20:30:30 -0400
> From: "Keman" <keman at interwolf.net>
> Subject: Re: [Biturbos4] All causes to turbo failures known?
> To: "Josef Hebenstreit" <josef.hebenstreit at hispeed.ch>,
> 	<biturbos4 at audifans.com>
> Message-ID: <000c01c43238$2c7b6c20$0100a8c0 at canis>
> Content-Type: text/plain;	charset="iso-8859-1"
>
>>> I have a S4 2,7 Biturbo/1999 and about 160.000 km. The chip-tuning
>>> pushed the performance to 310hp instead of 265hp. Even though I put
>>> my car to the service on a regular basis a turbo failure was
>>> inevitable!
>
> What kind of failure?
>
>>> 1)    Wear
>
> With infrequent oilchanges and poor quality oil, a turbos bearings can
> certainly wear out. They don't have to, Gerret for example will tell 
> you
> that their turbos will outlast any engine you attach them to so long as
> nothing breaks that controls the turbo.
>
>>> 2)    Boost leak causes over-spinning of the turbo -> rpm to high ->
>>> mechanical breakdown
>
> IMO there's your #1 cause. I highly recommend a good boost gauge .. 
> I've had
> one since 10k miles, even though my S4 still isn't chipped.
>
>>> 3)    Defect or mal-functioning air-mass gauge causes ECU to read out
>>> lower values for the air-mass flow -> ECU responses with lower fuel
>>> injection -> lean fuel-air ratio -> high temperature on turbine of
>>> the turbo -> thermal breakdown
>
> The O2 sensors detect this though and that's how you know the MAF is 
> gone,
> there are codes for reaching the adaptive limit rich set and a quick 
> glance
> at the MAF under heavy throttle shows much less grams/second measured 
> than
> what is really coming in.
>
>>> 4)    Dump valve or bypass valve
>
> When the bypass valves fail, they can cause an invisible boost leak 
> since it
> can dump air back in front of the turbo, but still behind the MAF 
> sensor.
> Aftermarket valves are a good idea.
>
> The wastegate diaphram can rupture, overspinning the turbo. Rare, but
> nothing is impossible. I've seen it once.
>
>>> 5)    Insufficient oil supply for the turbo - oil lines clogged or
>>> leaking
>
> Crappy oil and infrequent changes, sure.
>
>>> Normally the third case shouldn't be possible due to
>>> exhaust-gas-temperature sensor sitting between turbo and lambda
>>> sensor. ECU should detect high temperature (not only peak but also
>>> average value) and protect the turbo using the waste gate and/or
>>> switching over to limp program.
>>>
>>> What year of manufacture of the S4 has this exhaust-gas-temperature
>>> sensor?
>
> All biturbo S4's have two EGT sensors, one for each side just inches 
> after
> the turbo outlet.
>
>>> Is a K04-type turbo charger a solution to cope with the mechanical
>>> and thermal breakdown, independent whether the car is tuned or not?
>
> I honestly don't like the K04's. They're just a K03 housing with a 
> different
> turbine wheel. I've compared them side by side now. There are some
> ballbearing alternative turbos going around now that fit our cars 
> which are
> a much more appropriate design and are more efficient. If you're going
> through the hassle of replacing the turbos, you might as well go with
> something else.
>
>>> To you think the air-mass gauge is a problematic sensor? Do you have
>>> a remedy?
>
> It's problematic more often than not, but you'll get a check engine 
> light
> before it becomes a serious issue.
>
> - Keman
>
>>> Thanks,
>>> Joe
>