[urq] Need to Get a Specific Electronic Speed Signal From an UrQ Speedo......

Wed Feb 4 08:36:44 PST 2009

Patrick,
FWIW, the hall effect (5kt/q, CGT w/ digi, late ur q) and reed switch 
sensors (to present) are interchangeable. They both give a 0-12V 
(roughly) square ware output.  In fact, I just tested a '98 A6 
instrument cluster with an ur q/CGT/5ktq hall sensor and an RR ur q digi 
dash (pretty much the same as a US '86-'87 CGT digi dash) with a reed 
switch from an 01E on the bench just to remove any possible doubt.   
While I was at it, I also characterized the vehicle speed signal used by 
the ME5 ECUs.  It is simply a buffered version of the speed sensor 
signal with the same 0-12V output.  

As for the hall effect sensor not being compatible with the electronic 
diff lock, radio (GALA), etc., that is not true.  The RR and MB ur 
quattros have the speed signal for the diff lock control going directly 
to the output signal of the sensor (the diff lock, radio GALA signal and 
speedo input are all in parallel).  BTDT and it works fine.  My guess is 
that you had mistakenly connected the speed signal to the lock switch 
input, so that as soon at the sensor signal went low it told the control 
to unlock/lock.

Also, you DO need the speed sensor signal on AAN converted cars or they 
definitely will not run properly and will set a code.  BTDT.  Yes, it 
will run, but performance will be reduced.  Maybe it will work with an 
early V8 ECU, but I would bet that the later ones will alter the 
performance of the engine based on that signal not being present.

Steve Eiche
Shade Tree Software, LLC
http://www.shadetreesoftware.com
seiche at shadetreesoftware.com
800.419.6896 ext. 902
303.940.2468

Patrick Carlier wrote:
> The ur-q speed sensor for the digital dash produces a square wave .
> It's a 3 wire sensor so it's an active signal .
> The sensor is gear driven , just like a speedo cable .
>
> The V8 gearboxes I'm familiar with ( 01E types )  use a ring with 4 
> magnets
> and a reed contact as a speed sensor . So It's a passive signal .
>
> In the 01E style gearbox equipped cars , the instrumant cluster has a 
> chip that
> reads those reed contact pulses , converts them to pulses for a 
> stepper that drives the odo ,
> produces an analog signal for the speed indicator , and produces a 
> vehicule speed signal
> that goes to the cc and the rear diff lock control unit .
> I've added the datasheet of the chip , maybe it'll be of help .
>
> I know for sure that the 01E style vehicule speed signal that goes to 
> the CC and diff lock ( and most likely to the ecu to )
> is NOT compatible with the ur-q speed sensor signal .
> I've tried this on a 7A and six speed converted coupe GT quattro . I 
> use the rear diff lock controller from a later car .
> Normally it should disengage at 20 kph . With the ur-q speedsensor 
> connected it disengages immediatly if the car is pushed an inch .
> So I simply didn't connect it and if I ever use the diff lock , I'll  
> have to push the button again to disengage it .
> But this behaviour leads me to believe the VSS is supposed to be an 
> 0...5 volt signal , not a square wave .
> Haven't been able to scope it yet .
>
> I also dont have the vehulie speed signal to the ecu connected . It's 
> no big deal , the engine still runs perfcetly .
>
> Hope this helps
>
>
> Pat
>
>
>
>
>
> ----- Original Message ----- From: "Steve Eiche" 
> <seiche at shadetreesoftware.com>
> To: "Andrew Finney" <afinn1 at gmail.com>; <urq at audifans.com>
> Sent: Wednesday, February 04, 2009 12:48 AM
> Subject: Re: [urq] Need to Get a Specific Electronic Speed Signal From 
> an UrQ Speedo......
>
>
>> Andrew,
>> So did you get the ECU issue worked out?  As for the speed signal, it 
>> needs to be characterized it first.  If it is just a discrete DC 
>> pulse, that would be easy.  If it is a CAN message, then it becomes 
>> MUCH more difficult.  I don't have the wiring diagrams working for 
>> the A8, so I can't tell if they use a discrete speed signal or CAN 
>> messaging.  If you know someone with access to AESIS, it would be 
>> pretty easy to find out.
>>
>> If the signal is discrete, the best thing to do would be to check the 
>> signal and correlate it to the speed sensor signal.  The way to do 
>> that is to use two channels on an oscilloscope and compare (on an 
>> A8).  You may find that the speed sensor signal is a 12V pulse, and 
>> the speed signal sent to the ECU is just a "cleaned up" pseudo square 
>> wave signal of 0-5V with a pulse width that matches the speed sensor 
>> signal.  That would be pretty easy to do. Alternately, you could use 
>> an A8 cluster and see what the output is if you power it up, connect 
>> a speed sensor to it and spin it with the scope connected to those 
>> two signals.  That would likely be what I would do...
>>
>> I would assume that you want to use the analog ur quattro dash, not 
>> the digi, correct?
>>
>> Steve
>>
>> Andrew wrote:
>>
>> Does anyone know of a practical way to generate an A8 ECU speed 
>> signal from
>> the UrQ electronic (or cable) speedo sender? What I am wondering is 
>> if there
>> is a way to go back to the UrQ dash cluster from the A8 dash cluster
>> presently installed in my UrQ w/ 4.2L conversion. I'm not too versed 
>> in the
>> technical aspects, but it seems the A8 receives the same signal from the
>> transmission sender that an UrQ with a digidash does (same sender 
>> PNs) but
>> somewhere on the back of the A8 cluster that signal is modified and then
>> sent to the ECU. The need is to convert the signal coming from either 
>> the
>> cruise control sender or from an electronic sender into this A8 
>> singnal...
>> then I can ditech the A8 cluster. Anyone have any suggestions, or 
>> know of
>> someone off-list who can help? I'm wondering if Mockry or Eiche can 
>> weigh in
>> on this....Thanks everyone.
>>
>> Andrew Finney
>> 1985 UrQ w/ V8.
>>
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