J.P. Instruments EDM 760 Pilots Guide - Manual (Page 32)

Pre-ignition is caused by hot spots in the cylinder. Ignition occurs prior to
the spark plug firing. The EDM-760 depicts pre-ignition as a sudden red
line of the EGT on the analog display. This may occur in one or more
cylinders. The affected cylinder column(s) will flash while the digital
display will show an EGT higher than 2000°F. At this temperature pre-
ignition will destroy your engines in less than a minute unless you take
immediate corrective action.
Data Logging
On monthly intervals, you may choose to jot down peak EGT,
measurement sequence values, and cruise engine settings on a data
logging worksheet in the back of this book. Look for trends as well as
absolute values. DIF is a good indicator of the overall health of the
engines. Typical values are less than 80°F for a factory new fuel injected
engine, and less than 150°F for a carbureted engine. If you discover a DIF
spread greater than this, identify the effected cylinder and initiate
preventive maintenance.
Trend data for EGT and CHT is also of value. Any departure from a
cylinder’s baseline requires investigation. Refer to the “Engine Diagnosis
Chart” on page 24. Data logging as a means of identifying trends is of
considerable value in preventative engine maintenance.
Fuel Flow Option Operation
Select Switch
The select switch is a three-position toggle switch mounted on your
instrument panel near the display of the EDM-760. Any alarm warning
will appear regardless of the select switch setting.
•
In the EGT (Temperature) position only the installed
temperature (and battery voltage) measurements are displayed
in the digital display in either the Automatic or Manual
indexing modes or during the pilot programming procedure.
• In the FF (Fuel Flow) position only fuel flow measurements
are displayed in the digital display in either the Automatic or
Manual indexing modes or during the pilot programming
procedure.
Page 28 Engine Data Management