[Biturbos4] Re: All causes to turbo failures known?
cwurts12 at mindspring.com
Mon May 10 22:15:40 EDT 2004
Great post Keman! As always, thank you for your contributions.
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
> 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
> 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
> there are codes for reaching the adaptive limit rich set and a quick
> at the MAF under heavy throttle shows much less grams/second measured
> 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
> 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
> 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
> All biturbo S4's have two EGT sensors, one for each side just inches
> 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
> 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
> before it becomes a serious issue.
> - Keman
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