[V8] 93 Audi V8 / AT ZF4HP24A

[Tony and Lillie]

But, the thing is, the ECU doesn't need the hall signal to run, at least on 
the 3.6's. I can't see why they would change it on the 4.2's, but perhaps. I 
know this for a fact, because I unplugged mine and the car ran very similar. 
There was an ever so slight difference in responsiveness. That being said, I 
would never notice it if I were just driving the car, only because I was 
looking for a difference when I unplugged it. Actually, I expected the car 
not to start.

Tony

----- Original Message ----- 
Subject: Re: [V8] 93 Audi V8 / AT ZF4HP24A


First, one possibly significant detail: the speedo sensor is an
electronic "Hall" device. It senses the presence of a magnetic field
of a magnet that rotates past it.
This is different from the RPM and Crank Position sensors which are
simply coils of many turns of fine wire. They induce a voltage when a
piece of iron passes by.
So the Hall switch is an electronic switch with a 5-volt square wave
output, and the others are analog voltage output that must be
conditioned and converted to a digital signal.
The hall switch has 3 wires - 5v supply (from the ECU), output
signal, and ground.  If the sensor is known to be good, then the only
other logical choice I see is that the 5-volt supply is crapping out.
That seems to jibe with the other symptoms too.   That also means the
ECU is the most likely culprit.

Dave