> where is this "RPM SENSOR" as they show as a different device than the Hall. The RPM sensor (or Impulse Sensor) housing - the forward most sensor of the two that are back there (pre 87). It connects to the wiring harness directly under the MAF for the RPM signal. The other sensor located on the bell housing is a mechanic's Tool. It is the item you see on the Driver's side of the Intake - and connects to nothing electrically - it was as mentioned a Mechanic's tool - which didn't work very well I'm told.
The Hall has a very slight input to the LH Unit - and as Wally pointed out - the car will run without it. From what I understand - originally, the Hall was to determine the position of the Cam for precise Injection timing while the RPM Sensor provides the speed/accelleration input. If you trace the wires out, you'll find will finds that they trace all the way back to the Tach for the engine speed signal.
hth-
Jay
=============
At 02:59 PM 6/4/02, Tony Harkin wrote:
>where are the ACTUAL output wire (s) from the hall sensor which is located on the passenger side front cam area.
The output wires for the Hall Sensor are in a connector located in a
visible, but totally inaccessible connector located between the passenger
side cam cover and the fender - attached to the cam cover. Took me over an
hour's struggle to reattach the connector after the Hammer told me that I
had no Hall signal. Car ran perfectly with it disconnected - but a slight
power increase and 1 1/2 additional MPG after it was connected.
>is the HALL SENSOR the ONLY rpm signal "producer" for the
EZK/LH/ and instrumentation? On the schematics i see 2. 1) the "hall sensor"
and 2) "RPM SENSOR"
>
>where is this "RPM SENSOR" as they show as a different device than
the Hall.
The "Engine Speed/Reference Mark" sensor is in the top of the bell
housing.
If you look at page D28-11 in the back of Volume I-A, you can see the
output of the sensor. I don't think that it will give you the tach signal
that you need,
Wally Plumley
==========
> Ok I am wading though this 82 / S4 hybrid and studying the wiring diagrams. It appears I have a major void in my knowledge and the manual and wiring diagram are not helping. The S4 motor is a 91. So some questions.
>
> 1. What does a hall sensor do and can it be disabled. What are the symptoms when it is bad?
>
> 2. When the high speed sensor is activated what does it do? Can it be disabled? Where is the high speed sensor located.
>
> 3. What happens when a throttle switch goes bad.
>
> 4. Is there a good write up on the net about the LH system?
>
> Dan the Pod Guy
> Portia's Parts
Dan,
I regret that I can answer only one of your questions.
The hall sensor is a Hall Transistor, named for Dr. Robert N. Hall of the
General Electric research organization. It is a two or three terminal
semiconductor device whose conductance is influenced positively or negatively by
magnetic lines of force. Whether the change is positive or negative depends on
the magnetic polarity and the amplitude is typically in proportion to the number
of lines of force cutting the semiconductor junction.
In the Porsche 928 application I believe it is used to provide an impulse to the
microcontroller when a magnet affixed to the crankshaft passes near the Hall
transistor. If a single magnet is used, it likely detects TDC, if two magnets
are employed it may indicate that a cylinder is beginning the intake stroke. I
suspect that if it is disabled, the engine will not start or stop if already
running. You may want to read the book recommended by others for more details.
As with most semiconductors, the Hall device is highly reliable so long as it
not subjected to excessive voltage, current or temperature. It can short-circuit,
open-circuit, become unstable or thermally and mechanically intermittent.
Failures of mechanical devices, such as switches, relays, connectors and
potentiometers are much more probable though.
Testing the Hall transistor is simple. Just disconnect it from the circuit and
connect it to an ohmmeter (use diode test function if using a DMM) and pass the
gap of a horseshoe magnet over and around the device. If the resistance reading
doesn't change as the Hall device passes through the magnetic field, reverse the
lead polarity. If still no change, it is defective. Noise or intermittent
problems are best identified by observing the output waveform on an
oscilloscope or by substitution.
I hope this helps, should you suspect trouble in the Hall sensor.
jHh
1985 928S 4C M5 V8 32V Lamp Black
==========
At 04:55 PM 1/9/2005, Dan Brindle wrote:
>Ok I am wading though this 82 / S4 hybrid and studying the wiring diagrams.
>It appears I have a major void in my knowledge and the manual and wiring diagram are not helping. The S4 motor is a 91. So some questions.
>
> 1. What does a hall sensor do and can it be disabled. What are the symptoms when it is bad?
The Hall Sensor is mounted near the front end of the right head, and signals
camshaft position to the EZK (Ignition ECU). This info, combined with the output
of the two knock sensors, allows the EZK to retard the ignition timing when
detonation occurs.
If the Hall Sensor signal is faulty or absent, the EZK retards the ignition
timing, as it can no longer use the knock signals to retard the timing on demand.
> 2. When the high speed sensor is activated what does it do?
>Can it be disabled? Where is the high speed sensor located.
Not sure what you mean by "the high speed sensor". There is an RPM sensor,
located on the top back of the engine, reaching from the valley to the proximity
of the flywheel. It sends a pulse to the EZK every time the crank rotates. This
is used to fire the ignition and the injectors.
> 3. What happens when a throttle switch goes bad.
Depends upon which one goes bad. The idle switch tells the ECUs when the
throttle is closed. The ECUs adjust the mixture and the timing for idle
conditions. If it tells them the throttle is closed when it isn't, the timing is
retarded and the mixture is richened. The WOT switch tells the ECUs when the
throttle is open more than about 70%. The mixture and timing are set for full
throttle conditions, and the LH ECU goes into open loop.
> 4. Is there a good write up on the net about the LH system?
Best bet is one of the manuals on Bosch Fuel Injection. I normally use "How to
Understand and Modify Bosch Fuel Injection and Engine Management", ISBN
0-8376-0300-5, by Charles O. Probst.
Wally Plumley
928 Specialists
Visit our new web store, with over 20,000 928 parts on-line!
www.928GT.com
----------
The hall effect sensor is a typical rotational speed sensor based on
proximity. It is a wear free, maintenance free, precision sensor insensitive to
dirt or moisture. The sensor informs the EZK about the engine (passenger side
camshaft) position.
Testing the hall sensor is like this:
The sensor has 3 pins.
1= power supply 5v
2= open collector output
3= signal ground
You apply 5v power to pin 1 and ground to pin 2. Then use a 1k resistor to
pull-up the output as it is an open collector output. Taking a reading from pin
2 now gives you the expected response if the sensor is ok. The sensor senses the
metal moving to and away from the sensor. You can test that on your bench.
regards
Theo