[Biturbos4] testing testing trying to post....

Tue Dec 7 17:10:35 PST 2010

Having recently found out that the 945 degrees C may not indicate bad sensors, I thought perhaps there was a leak at 5 psi and beyond in the pressurized part of the intake manifold system. To test for this, I spent some time fabricating a set of hoses and adapters to pressurize the intake manifold/plenum.

1) Blocked off the main intake (coming from the MAF sensor to the Y pipe).
2) Removed the crankcase vent pipe, and added in a pressure adapter from my air compressor,
3) set the outlet pressure at 5-7  (hard to guess down so low), connected the hose to the fitting.

Air is now going into the upper Y pipe, and should be pressurizing the system, including turbos, up to the throttle body (where presumably the butterfly valve should keep it from going further.

I now have a continuous air flow going into the intake, and there is a rushing sound of air.......but pressure never builds up. I cannot find where the air is going......if appears to be going into the engine. Unlike my older Audi, I seem to have no way of knowing if the butterfly valve is open or closed...is there some way to verify this?  I cannot seem to find why so much air is vanishing, even at very low pressure, since the pressure is never getting a chance to build up in the system.

Has anyone had this problem and overcome it?  The Bentley does not give any hints...

Thanks,

Alan

  ----- Original Message ----- 
  From: David Pramanik 
  To: alancordeiro at comcast.net ; biturbos4 at audifans.com 
  Sent: Monday, December 06, 2010 3:01 PM
  Subject: RE: [Biturbos4] testing testing trying to post....

  Alan,

  The EGT sensors on the 2.7T have an operating range of 945C to 1035C.  Under most driving conditions (your idling test included), exhaust gas temperatures will be below 945C so the sensors will read their minimum value 945C.  So what you are seeing isn't necessarily a problem.

  The problem is that when the sensors when they fail, they read 1035C.  This causes the ECU to think that exhaust gas temperatures are too high and the ECU responds by significantly increasing the fuel injector pulse width, which can cause stumbling or missing.  If you log with VCDS whil the car is missing and see 1035C for the EGT values, it could be that the EGTs are indeed faulty.

  But given how expensive the EGT sensors are, I wouldn't replace them without doing more diagnosis.  Most often when I've seen missing under boost, it is due to old or worn sparkplugs.  Simply swapping in fresh plugs will typically alleviate the issue.  If that doesn't solve it, use VCDS to pinpoint the cylinder(s) that are misfiring and swap the coilpacks around to see if the misfiring moves with the coils (indicating a faulty coil).  Baring that, you could have an injector that is partially clogged or not responding properly.

  If you do find that the EGTs are infact faulty, they can be rather tricky to replace.  You'll probably need to bend some 17mm wrenches in order to be able to get a good angle on the sensors.

   VCDS is the closest thing to the VW/Audi factory diagnostic tool (and in some cases, it has capabilities that the factory tool does not), so it is well worth the money if you plan on owning and maintaining an aging Audi.

  -Dave Pramanik

  > From: alancordeiro at comcast.net
  > To: biturbos4 at audifans.com
  > Date: Sun, 5 Dec 2010 15:36:38 -0500
  > Subject: [Biturbos4] testing testing trying to post....
  > 
  > Good afternoon to all list members. Since I signed up November 5th, it 
  > appears that all messages from the list have ended.....if indeed I am the 
  > jinx who slowed the dribble to a full stop, I need to apologize.
  > 
  > If not, since a month has now passed with no message, I thought I would 
  > create one to jump start it.
  > 
  > A brief introduction, my name is Alan Cordeiro, and I recently gave up a ten 
  > year long ownership of a '91 200q with 285k miles and replaced it with a 
  > 178k mile 2001 S4.
  > 
  > My original quattro vehicle was a 1986 5000CSq....and I have been a list 
  > member of the original "quattro" list since 1995, from the days we posted to 
  > quattro at swiss.net, (but gave it up to focus on the more specific 200q20v 
  > list, and now hopefully this list.
  > 
  > As with all previous cars, the current S4 is also performance enhanced, 
  > including APR stage 3 chipped, RS4 turbos and clutch, piggie pipes, 3" dual 
  > inch exhaust, and Vogland coilovers.
  > 
  > I am looking for advice on two items:
  > 
  > 1) Having missing at high boost.......it would appear to be defective EGT 
  > sensors. Using a friends VCDS, we noted both read 945 degrees C 
  > continuously, even with the engine idling. Does anyone know what made them 
  > both go bad suddenly?
  > I have the set of two on order, and expect them in a few days. Please give 
  > me any advice on how best to replace them.
  > 
  > 2) Considering buying a good diagnostic tool.....possibly a ROSS-TECH VCDS, 
  > but wondering about all the other much cheaper tools appearing on e-bay. 
  > Have anyone of you bought these? Do they work, and what is the downside? The 
  > prices seem very attractive,
  > 
  > Thanks,
  > 
  > Alan Cordeiro
  > 
  > ----- Original Message ----- 
  > From: <biturbos4-request at www.audifans.com>
  > To: <alancordeiro at comcast.net>
  > Sent: Friday, November 05, 2010 9:01 PM
  > Subject: Welcome to the "Biturbos4" mailing list
  > 
  > 
  > > Welcome to the Biturbos4 at www.audifans.com mailing list! Welcome to the
  > > Biturbo S4 List at audifans.com
  > >
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