Suspecting bad ECU and master cylinder. Please help confirm. (pretty long)

jlagnese at jlagnese at
Tue Nov 10 15:53:11 PST 2009

The brake problem is likely the master cylinder.
I've replaced it on mine.
---- Original message ----

  Date: Mon, 9 Nov 2009 18:16:02 -0800 (PST)
  From: Dan Bozga <audisport44 at>
  Subject: Suspecting bad ECU and master cylinder.
  Please help confirm. (pretty long)
  To: 200q20v at
  >Hi everyone,
  >I'll start by saying that I've been part of this
  mailing list before, many years ago. I doubt
  anyone will remember though. I'm on my 4th 20V
  now having owned a red one at first followed up by
  a black and then panther black. I haven't had one
  for quite a few years but I recently acquired a
  pearl white in hopes of using as a daily driver so
  I can stop driving my '02 B5 S4 all the time. I've
  put way too much time and money into that car so I
  really need to start racking up miles on something
  else. That's where the 200 comes in.
  >I bought the car from a guy that seemed to be
  clueless about it or what it really was and he
  thought it had a bad turbo. This was according to
  his mechanic that works on BMWs, so you can
  imagine how familiar he is with Audis. The turbo
  itself is fine, not seized by any means and the
  shaft play is so minimal it's one of the best I've
  seen. There were many other little issues here and
  there which I've been fixing but the two main
  problems still remain.
  >1. The brakes.
  >The brake light stays on constantly. At first
  everything is ok, but eventually after driving the
  car for a very short while they begin to seize up.
  The brake pedal actuation point drops down and the
  car wants to haul to a stop and you really have to
  use the engine to overpower the brakes and get it
  moving. I've checked all the calipers because at
  first I thought it was corroded carrier pins. All
  4 calipers seem to have been replaced pretty
  recently. I took out all the pins front and rear
  and cleaned and greased them either way. I no
  longer think it's a matter of stuck carriers and
  somehow doubt it would be pistons either. The
  brake servo (part that connects to the firewall
  and brake pedal) was leaking pretty badly so I
  thought that might be why it seizes. I replaced it
  with a used but good unit with about half the
  miles of mine (198k on this car btw). The leak has
  stopped but the problem is still there.
  >I've checked power assistance after the car is
  stopped and I have plenty of it. I've pumped the
  brakes like 40 times and there was still
  assistance. All of this leads me to believe that
  the pressure accumulator is fine and that the next
  thing I should be replacing is the master
  cylinder. Once you park the car the pedal
  actuation point gradually start to return and you
  can hear a "seized piston becoming loose" type of
  sound when this happens. Before I throw more parts
  at it I wanted to see what you guys think and if
  you agree with my direction here.
  >2. The engine.
  >It's a bit hard to start at first and wants to
  stall but once it gets going the idle is smooth
  and stays on no problem. I think the issue here
  might be fuel pressure decreasing after shut off.
  If you stop it, it starts right back up. This
  problem is only there after its been sitting for a
  while. I've checked the carbon canister solenoid
  and it doesn't seem to be getting power. I did the
  test for it by jumping the posts under the knee
  bolster and there was no clicking sound at all. I
  replaced it with another unit and that didn't
  solve it either. I measured resistance on both
  valves that I have and they check out. Bentley
  says there is supposed to be continuity between
  terminal 2 from this valve/solenoid connector and
  fuse #24 but there was none. I tried tracing wires
  but couldn't come up with much. I don't know
  exactly how they are routed, it gets pretty fuzzy
  once you get between the fuse box and under dash
  relay wires. Speaking of relays, there is an
  > empty spot(knee bolster) with actual wires going
  to it labeled "IRA relay". Any of you know what it
  stands for and if it's supposed to be present?
  There are also two spots for relays listed on the
  fuse box cover for AC under spots "6" and "11".
  Are these also supposed to be present or are they
  empty spots? They both have wires going to them
  too. Haven't tested AC on this car yet. The
  seller said it doesn't work anyways so I assume
  bad compressor (looks like it leaks) but that
  hasn't been my priority right now.
  >When in neutral you can open the throttle all the
  way and rev the car up but it gets stuck around
  4250 RPMs at which point it begins to sputter
  violently and pop VERY loudly. I think it's
  hitting the fuel cut because the dash displays 1.9
  bar when this happens. That's the highest I was
  able to get it so far. I've never seen an Audi
  make full (or more) boost in neutral so this led
  me to believe the car is overboosting for some
  reason. When this violence takes place you can
  hear the ECU clicking constantly too. If you just
  let it idle after one of these episodes (aka
  hitting that 4250 spot for a few seconds) the
  wastegate frequency valve starts clicking as if
  it's receiving a bad signal. Now I've checked this
  valve with one out of my S4 and although they are
  not the same part numbers I figured it should
  still show a sign of improvement. Nothing changed.
  I've been down the road of checking every
  component with the output test and a multimiter.
  > seems to work fine. 
  >There were a couple boost leaks which I fixed and
  now the system can hold 20psi no problem. I took
  apart the wastegate suspecting a bad diaphragm but
  it is in perfect shape. No holes at all. I checked
  it very well twice. I know what a bad one looks
  like from my first Audi ('86 5K CS Q) and can
  assure you it isn't the problem. I feel like I've
  eliminated everything at this point which made me
  start looking at the ECU. I had a feeling it
  wasn't stock, even thought the rest of the car is
  all original. Well, what do you know? When I took
  it apart I noticed the higher value(2.5) BOSCH
  pressure transducer and aftermarket eproms (both
  of them). I took pictures of all of these so maybe
  you guys can help me figure out what company's
  software this is. The little white labels say HOB 
  on top outlined by black marker. The rest should
  be very legible. Also when you take these stickers
  off there is a little glass window which allows
  you to see inside the chip. Took a
  > picture of that too hoping it might help
  identifying them.
  >The fault codes I get are:
  >2111 (rpm sensor). I checked out the flywheel and
  all the teeth are fine. So are the timing
  reference pins. This led me to believe it might be
  a faulty RPM sensor. I replaced it with a known
  good one and it made no difference.
  >2341 (oxygen sensor limit exceeded). The car is
  old and I don't know its history so I figured I'd
  replace the O2 sensor anyways with a genuine BOSCH
  OEM unit (no splicing). Of course this didn't
  solve the problem but I thought I'd put it out
  >What else can I say to help...
  >I checked the distributor gear and it actually
  has the updated metal unit so no issue there
  either. I've done checks on everything from air
  temp sensor to TPS and everything in between. It
  all looks fine and/or measured within spec.
  >When the car is under load you can still only get
  it up to 4250 RPMs before all hell breaks loose.
  You have to get it up there gradually though. It
  WILL cut off at any point if you attempt to floor
  it (unlike in neutral).
  >Pretty much what I've come up with so far is that
  a part of the ECU is faulty and causing mayhem.
  What would limit the amount of boost the car
  makes? The pressure transducer or one of the
  eproms? I'm thinking this is where the codes and
  overboost are coming from. I'd love to swap the
  ECU with a known working unit but I don't have
  that luxury. Maybe putting in stock chips and psi
  trans. might work. I don't know, I'm open for
  suggestions before I go out buying another
  computer. The board seems to be socketed but I
  don't have the stock chips or transducer to check.
  >I'm in the Washington D.C. are if any of you are
  local. Or, I could perhaps send my ECU to one of
  you guys to test it in your car. I'd offer payment
  for anyone's trouble.
  >Here's a link to the 5 pictures I took:
  >Please click on each one you'd like to see and
  then click again to view the full size.
  >Thanks for listening. I'm sorry it's so long, but
  I tried to make it as detailed as possible. If you
  need ANY other details just ask away.
  >Dan B.
  >P.S. I did a fresh full on timing belt kit on
  this car so there is no problem with any timing
  marks being misaligned. It had no impact on my
  issue but I had to do it anyways. Again, not
  knowing the history of the car.
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