Re. Suspecting bad ECU and master cylinder. Please help confirm

Ben Swann benswann at
Tue Nov 10 09:29:19 PST 2009


1. Replace the Master Cylinder and bleed the system - all wheels, essentually to flush
out the old fluid.

2. a. Pull codes if you can - OK I see you did that.  The RPM sender code could actually
indication the distributor is going out of window.  Check the timing belt and verify TDC
- not just by the harmonic balancer. But by the flywheel - sometimes I test TDC and
locate flywheel mark with help of rod placed in #1 spark plug hole while slowly turning
engine til finding highest point the rod travels - then you can see the flywheel mark
and clean it.

2. b. Not all relay spots are filled - some are for headlight washer, aux. lighting,
other options. 

2.c. Replace O2 sensor (obviously) and lcear codes.  You can use generic O2 sensor and
splice in to original connector - usually much cheaper.

3.  I'm in Annapolis, so not far from you and have lab setup over my garage and can help
with the ECU.  I have units that we can swap out.  See



[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
Message-ID: <526586.92893.qm at>
Content-Type: text/plain; charset=iso-8859-1

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

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. Everything  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 there. 

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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