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on, the LED should illuminate.
You can test either of these inputs by temporarily tapping the input to ground. Remove the signal wire
from the Main Module first, replacing it with a test wire connected to the input terminal. Then short
this test wire to ground by repeatedly tapping the wire to ground. (There are many convenient ground
terminals nearby in the Main Module.) This tapping should cause a jump in the RPM reading. If it
does not, then call Computech for customer support.
If the tapping test above works, but you still don’t get a Drive shaft (Input shaft) RPM reading in
motion, then try adjusting the sensor so that the gap to the magnet is as small as possible without
touching the magnet or balancing weights. Next, turn the drive shaft (input shaft) until the magnet
moves from more than 2" away from the sensor to closer than 1/4" to the sensor. The LCD display
should show a small nonzero number for a moment. If you can't move the drive shaft (input shaft),
then you may remove the sensor from the bracket and then move the sensor from far away to nearby
the magnet. If you do get an LCD display reading, then the Drive shaft (Input shaft) RPM input is
working properly.
If Drive shaft (Input shaft) RPM remains zero, unplug the sensor and work with the connector on the
cable coming from the junction box. Short a screwdriver or wire between the two conductors of the
connector. An LCD display reading should result. If it does not, call for customer support.
D
RIVE
SHAFT
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RRATIC
OR
N
OISY
You may find yourself in the following situation. Your in the shop and your car stationary. The Drive
shaft RPM reads zero on the LCD display with the engine off, but registers random values when the
engine is on. If you find this to be the case, then your Drive shaft RPM sensor circuit is picking up
ignition noise. The Main Module includes a Drive shaft RPM sensor circuit that is already filtering
much of your ignition noise out. Evidently, your ignition system generates such strong electromagnetic
noise that the filter cannot eliminate all of it.
You have a few options at this point. First check the location of your ignition module and your ignition
coil relative to your Drive shaft RPM sensor, wiring,
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Main Module. If it is possible to put
more distance between them, then do so.
If you still can't eliminate the noise on your Drive shaft RPM sensor, then inspect your ignition wiring.
Most likely, you have a zero resistance (solid core) wire from your coil to your distributor, a zero
resistance rotor button, and zero resistance spark plug wires. You will need to replace these wires with
a higher quality radio noise suppression type wire. Contact Computech customer support for details.
Copyright c 2008 Computech Systems Inc. 48
