Interesting ride to work

[urq]

... when that happens you would not expect the tach to immediately drop to 
zero as reported ...

On the urq/WX engine there are three sensors that can cause the loss of 
spark that would cause the tach to drop immediately like that ... the Hall 
Sender in the distributor, the engine speed and and engine reference sensors 
which mount on the bellhousing and sense flywheel teeth and the reference 
pin.  My urq experience would make me lean toward the Hall Sender (either 
broken or a change in cam timing) ... of course if the cam timing changed 
you would not expect the immediate recovery upon restart.  My experience on 
the V8s is that the flywheel senders can and do fail ... and yes, they are 
available new for $100-150 ... perhaps not the ones specific for the WX, but 
ones that will work.

The other possibility is on the other end of the F/TCU ... that being the 
ignition driver module has failed and you lose spark that way ...

Unfortunately it is going to be difficult to identify the flaky sensor as 
there is no diagnostic capability on the WX/MAC-02.  I've been tempted to 
build a jumper block that can install in line to the connector to the ECU 
which would allow you to monitor all of the I/O ... much like the box Audi 
uses for diagnosing older ABS systems ...

Steve B
San Jose, CA (USA)


> My 4000 once quit like this. Bad Fuel Pump Relay.
>
> LL - NY
>
> On 3/15/07, DGraber460 at aol.com <DGraber460 at aol.com> wrote:
>>
>> This AM, I am jaunting on to work with the usual Audi flare when at  ~60
>> mph
>> steady speed that old URQ went spark dead. Tach dropped to zero.  No
>> noises,
>> bumps, etc. I coast to the side of the road in gear all the  while
>> jiggling
>> everything I can think of (including the ignition switch) to no  avail.
>> All the
>> other electrics worked fine but the tach didn't even bounce.
>> Once stopped, I offer a heavy sigh of "What Now?!", and turn off the
>> ignition. Figuring I had nothing to lose, I turn it back on and crank it
>> and it
>> fires right up and ran fine the rest of the day.
>> My first guess is the TDC flywheel sensor. Is there anything else that
>> will
>> totally cut spark this way?
>>
>> Maybe I have a Microsoft programmed ECU, and just wants to be "rebooted"
>> once in a while.
>>
>> My other URQ did something similar about once every 9 months, but
>> would  buck
>> and backfire and finally completely die. It would also start right up
>> after
>> the "reboot". Not sure but I might be using the same TDC sensor from
>> that  car.
>> Are these sensors still available new? If so from where? The used spares 
>> I
>> have are all a bit dodgy.