TACH LEARING MODE
The TACH LEARNING MODE is the most reliable and consistent method of engine speed sensing. This wire looks
for the pulsing signal that is created to monitor the engine speed or fire the coil. Most modern ignition systems utilize
a crankshaft sensor to monitor the engine speed. There are 4 different types of signals that may provide adequate
signal for TACH SENSE:
Type 1
- Will be a computer-controlled ignition. On these systems the engine speed reference (tach) may come
from several possible locations. The wire may be found at: Distributor, Ignition Module, Coil Pack, Engine
Computer, or Crankshaft Sensor.
THIS WILL BE THE MOST RELIABLE AND CONSISTENT SIGNAL.
Type 2
- Will be a standard ignition coil. Connect the RED/WHITE 22-gauge wire to the negative(-) side of coil.
Note: The coil MAY NOT BE A GOOD LOCATION FOR TACH SOURCE. The coil wire may be too noisy for the
system to detect a clean signal and/or the vehicle uses a Multi-spark ignition system that varies the spark.
Type 3
- Will be computer controlled fuel injection solenoids. This wire can be found at the Injectors in the
engine compartment or at the engine computer.
Type 4
- Will be the Alternator Stator pin on the alternator. This is found on many GM and Ford Diesel trucks
from the mid 1980's through the mid 1990's.
Use the Tach Finder Mode below to locate your tach source wire.
TACH-FINDER MODE
TACH-FINDER MODE is a unique feature to help installers easily identify wires which may be POSSIBLE sources
for an engine speed reference by using the same RED/WHITE wire to probe ANY wiring, WITHOUT RISK TO THE
COMPUTER SYSTEMS.
Tach-Finder may be operated by following the procedure below:
1) OPEN HOOD (ground GRAY hood switch wire) and Start engine.
2) Depress and Hold the BRAKE PEDAL and THEN PRESS THE PROGRAM BUTTON until the parking lights
come on solid.
3) Connect the RED/WHITE tach wire to a scribe or sharp probe.
It may be necessary to extend RED/WHITE wire.
Probe the wires that may provide the proper signal. Warning: be certain to protect yourself from electrical
shock!!
4) Start probing wires, When a wire with a pulsing signal is probed, the parking lights will start FLASHING.
5) At this time, turn engine/ignition off. Parking lights will stay ON.
6) Verify tach signal. Turn Ignition ON but DO NOT START ENGINE and probe the same wire.
A) If parking lights start FLASHING, you have found a DATA wire. This wire will tell the system the engine is
running even if it the engine is not running. RESTART ENGINE and Repeat steps 4-6 with another wire.
B) If parking lights stay SOLID then START ENGINE. If park lights stay on SOLID after engine is started,
there is no tach source. Repeat steps 4 through 6 to locate another wire. If park lights start FLASHING
after engine is started, the tach source
may
be valid.
7) Turn engine OFF, park lights will remain ON. Permanently connect RED/WHITE wire to the located tach lead.
8)
Now it is time to
PROGRAM the TACH REFERENCE:
A) Start engine (with hood open), parking lights should start flashing.
B) Depress and hold BRAKE PEDAL down.
C) Press and hold PROGRAM SWITCH for 2 seconds. Parking lights will stop flashing while button is
depressed.
D) Turn Ignition OFF, close hood. Parking Lights will still be ON. Tach Programming is now complete.
E) Depress BRAKE PEDAL to clear parking lights.
Summary of Contents for COOL START RS-901
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