[urq] WX ECU Question

[Michael Hopton]

When the MC engine was first installed in my '84 the car
would start and run fine from cold. Then the odd time when
hot it wouldn't start. The hot engine was enough to shift
the timing pin out of the distributor window. A few degrees
of turning the distributor fixed the problem.

Similarly on my S6 (and this is a known problem on a number
of S4s and S6s) the hall senders would fail when hot, you get
the check engine light coming on momentarily. This is fine
if you don't switch off the engine because it won't start
until it has cooled down and the hall sender is functional 
again. 

I was left outside a beer store with an engine that wouldn't 
start. You get strange looks packing snow on to the cam hall 
sender trying to get the thing to cool down so you can get
your beer home :)

Cheers, Mike 

-----Original Message-----
From: Buchholz, Steven [mailto:Steven.Buchholz at kla-tencor.com]
Sent: Thursday, February 26, 2004 3:30 PM
To: 'urq at audifans.com'
Subject: RE: [urq] WX ECU Question


... all right ... I stand corrected!

I have reverse engineered the circuitry on the MAC-02 and can tell you that
there is a gate which is supposed to use the distributor signal to mask off
every other TDC pulse ... I guess what is happening is that the open circuit
at the Hall Sender effectively opens that gate ... which means that the ECU
is seeing every TDC pulse.  OK ... perhaps the engine will work that way ...
not sure I'd try to depend upon that however ...

It was surprising to see the note about other engines allowing operation to
continue with the timing signals out of spec ... assuming that at some point
in time the signals did have the proper relationship this would tend to mean
that something is changing.  Given that most of the engines we're talking
about are interference engines I would rather have the engine stop running
and give me a fault code than worry about having the TB go ...

Steve B
San Jose, Kaleefohnia (USA)
> 
> Steve,
> I disagree. Unplug the hall sender "once" the engine has started
> on a WX and the engine keeps running. It is for start up only.
> 
> The later cars flag codes if the pin is outside the window but
> will keep running too, this goes for Motronic (S6) with cam shaft
> driven hall senders.
> 
> regards, Mike
> 
> -----Original Message-----
> 
> Yes.  In fact the signal from the Hall Sensor on the 
> distributor actually
> gates the reference pin signal so that only every other TDC 
> is registered by
> the ECU.  If the cam timing shifts or the Hall Sender signal 
> is changed in
> any other way so that the reference signal falls outside the 
> window the
> engine will not run ... even if it was running before.
> 
> The MC is very similar in this regard ... I am not as 
> intimate with the ECU
> circuitry to know whether or not there is an actual logic 
> gate outside the
> ECU as is true for the MAC-02, but the MC will also stop 
> running if the
> reference signal goes away.  Since the engine has an odd 
> number of cylinders
> it is a safety feature.
> 
> The only Audi engine I'm familiar with that only depends upon 
> the reference
> pin matching the dizzy at startup is the V8 engines similar 
> to the PT.  
> 
> Steve B
> San Jose, Kaleefohnia (USA)
> > 
> > Does the ECU check if the ignition timing reference pin 
> falls inside the
> hall sender
> > window on a WX engine? Or, is it just used on start up to 
> synchronize the
> head
> > with the crank? After startup you can unplug the hall sender and the
> engine
> > keeps running which makes me believe the reference window 
> is not checked.
> > I know this is the case for the MC engines where the ECU 
> will throw a
> code.
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