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

Mike Sylvester mike at
Tue Nov 10 08:32:30 PST 2009

There is no way you can get any boost without a load.
So if the display shows anything above 1.0 when you are in neutral the
signal from the pressure transducer is incorrect.
It probably is hitting the fuel cutout since the ECU "thinks" the boost
is too high.

The ECU is clicking?  There is nothing inside the ECU that should make
any noise.

Maybe someone did a bad job soldering in the 2.5BAR transducer.

You don't want to remove that label on the chip for very long.  That
type of chip is erased using UV light.


> Original Message:
> -----------------
> From: Dan Bozga audisport44 at
> Date: Mon, 9 Nov 2009 18:16:02 -0800 (PST)
> To: 200q20v at
> Subject: Suspecting bad ECU and master cylinder. Please help confirm.
> (prettylong)

> 2. The engine.
> 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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