Dynojet 248x: Installation Guide - Manual (Page 49)

Document #98219101 4 - 5
Connecting The RPM Pickup
Your Dynojet dynamometer includes a primary wire inductive
pickup and two secondary wire inductive pickups. These small
“clothespin like” inductive pickups are used to sense RPM. An
RPM pickup is required if you want to view torque graphs.
Generally you will use one secondary wire inductive pickup on a
spark plug wire. Vehicles with wasted spark ignition systems may
require two secondary inductive pickups. On a wasted spark
ignition, typically one coil will be connected to two spark plug
wires. Attach one secondary pickup to each of these wires. If the
pickups are connected to two plug wires that do not fire at the
same time, an erratic RPM readout may occur. The primary wire
inductive pickup senses RPM pulses from the coil. Although this
pickup location generally works better, it is harder to find the
correct location to connect the RPM pickup.
Note: If a pickup is not being used, disconnect it from the
dyno electronics to prevent any stray pick up of signals.
The optional Optical Sensor is useful on diesel powered vehicles,
MSD ignitions, and other high RFI ignition systems. For more
detailed information on the Optical Sensor, refer to the Optical
RPM Sensor Installation Guide (P/N 98295109).
CAUTION: Inductive pickups are very fragile. The ferrite core
can easily be damaged and is not covered under warranty.
Dropping, snapping, vibration, and heat can all damage the ferrite
core.
The dyno electronics RPM module contains the electronics that
sense the RPM pulses. An auto-gain circuit looks at only the peak
voltage of the vehicle’s spark, ignoring the lower voltages to help
reduce electronic noise problems. Wasted spark ignition systems
will produce a lower voltage level on the exhaust stroke than the
compression stroke. By definition of the auto-gain circuit, lower
voltage spark levels will be ignored, missing every other spark the
vehicle would produce.