Dynojet 224: Pit Installation Guide - Manual (Page 36)

In Ground Model 224 Automotive Dynamometer Installation Guide
C H A P T E R 3
Connecting the RPM Pickup
3-4
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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).
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 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.
RPM P ICKUP D ESCRIPTIONS
RPM pickup description
Secondaries (Non- wasted spark system) Use one secondary pickup. Unplug the other pickup from the RPM
module and set the degrees between plug fires to 720° in WinPEP.
Secondaries (Wasted spark ignition
system)
Use two secondary pickups. Attach one pickup on each spark plug
wire on the same coil and set the degrees between plug fires to
360° in WinPEP.
Primary pickup Attach the primary wire pickup to the primary side of the coil. Set
the degrees between plug fires by taking 720/number of cylinders.
For example, the number of degrees between plug fires on a V-8
engine with a single coil is 720/8=90 degrees.
Optional Optical RPM Sensor Attach the sensor wire to the RPM module, also be sure to plug in
the small power lead into the CPU module. The other end of the
wire attaches to the Optical Sensor. Set the degrees between plug
fires to 360° in WinPEP. Refer to the Optical RPM Sensor
Installation Guide (P/N 98295109).