[urq] MAC 02 Pressure Transducer failure?

[Buchholz, Steven]

... actually the computer does not "adjust everything" ... all it really
adjusts is the ignition timing ... and pinging is something that can
occur even without a spark.  You may have a screwed up mixture in one or
more cylinders caused by malfunctioning injectors.  Before getting too
far into things you might want to investigate this by reading the spark
plugs.  

You may want to consult the IST docs to help with your understanding ...


	http://www.quattro.ca/Urq/urq-IST-Introduction.pdf

On page 18 it shows how the F/TCU changes the timing based on boost ...
if you had a PT that was indicating there was no boost, when in fact the
engine is seeing full boost the diagram shows that the timing would
likely be *retarded* from optimum (for example the ignition timing at
4000RPM at 0 bar is almost 40 degBTDC, where at max boost it is
something like 15 degBTDC).  I just read the doc ... it indicates that a
faulty Intake Air Temp sensor might be responsible for pinging.  

Nevertheless, the faulty pressure transducer is something you should
fix.  It could well be contributing to the problem ... at the very least
it means your engine is not operating optimally.  Unfortunately you
can't just hack in a constant value for the manifold pressure ... the
F/TCU looks for the boost to be too high at low RPMs and will shut off
the fuel pump.  It is pretty clear that the PT module that was used with
the MAC-02 is NLA, but there's no reason a functional equivalent could
not be manufactured ... this would provide a good opportunity to put in
a higher rating device e.g. 2.5 or 3.0 bar, which could be combined with
a remapping based on the info RDH compiled on the MAC-02 to allow higher
max boost.  

There is some justification for going ahead with the MC/MAC-11 swap ...
there the big gain is the knock sensor and WGFV boost control mechanism.
The downside is those stupid hydraulic tappets that Audi uses.  

Hope this helps you with your troubleshooting and decision making!

Steve B
San Jose, CA (USA)
> 
> SO the next thing is, how do you get pinging, if the computer adjusts
> everything?
> 
> Martin P tells me about the known 'pressure transducer failure'.
> 
> So today I wired up some leads to the transducer, so I could measure
it's
> output while driving.
> 
> Surprisingly enough, there was no output. I assume that means the ECU
thinks
> it's seeing full vaccum all the time.
> 
>  That cold explain the pinging..!
> 
> So my questions are:
> 1) What's the chance that replacement transducers are available?
> (Probably unobtanium, so I may as well go to a MAC 11 ECU and harness,
as I
> already have the block, head and turbo..?)
> 
> 2) I'm sure I've seen a spreadsheet somewhere, that shows transducer
output
> vs transducer pressure. Anyone else know where to find that?
> 
> I could then substitute the pressure transducer output with a fixed
voltage,
> closer to what the ECU would want to see for near full boost. At least
then,
> It won't ping so much (But have other side effects of never changing
value
> either).
> 
> 3) Or any other ideas?
> 
> It's the MAC 02 with the 'yellow' label, if that makes any difference?