J.P. Instruments EDM 740 Pilots Guide - Manual (Page 28)

Page 28 Engine Data Management
Expanded Leaning Procedures
Lean Of Peak mode: During the ‘lean of peak’ process, the EDM hunts
for the last cylinder to peak. This is because, ultimately, you want to
have ALL cylinders operating on the lean side of peak. You will final
adjust your mixture to this cylinder. To provide a unique graphical
depiction during lean of peak operation, the columns become inverted
after the first EGT goes just below peak. Each EGT column then
originates from the top of the display and drops downward. As each
subsequent EGT goes past peak, its column will begin falling. The
columns length depicts how far the EGT has dropped below its original
peak. In this mode, each segment is 5° F. You will continue to lean until
the last EGT peaks (note: never lean to the point where the engine is
running rough). When the last EGT peaks, its respective column will
flash and the word
RICHEST appears . The scanner digital readout will
now show the current temperature difference from where peak EGT
occurred and also the current fuel flow (if so equipped). Note: if you
hold the LF button, the display will show the captured peak value of the
‘last EGT to peak’ and also the difference in fuel flow (if FF equipped)
between the first and last to peak (also known as the GAMI Spread).
This can be a good indication of how well your injectors are balanced
(the smaller the FF difference, the better the injector balance). Tapping
STEP exits the lean find mode and automatic scanning resumes.
Leaning Turbocharged Engines: The leaning process for turbocharged
engines is by reference to the first EGT or TIT to reach peak. Therefore
you should use the Rich Of Peak mode. The factory TIT red line may limit
the leaning process, depending on flight conditions. TIT red line is generally
1650°F to 1750°F. If TIT exceeds red line (but not by more than 99°), the
EDM will allow you to continue leaning for one minute before a TIT alarm
activates, implying you should enrichen the mixture.
NOTE: in some cases, TIT can read approximately 100°F hotter than
the hottest EGT. This is because of unburned fuel in the exhaust
igniting and is not necessarily abnormal behavior. The reduced size of
the
JPI Hastaloy-X-tip probes produce faster response and are more
accurate than the massive factory installed probes. Therefore a
JPI probe
may read as much as 100°F higher than the factory installed probe.
However, the certified factory-installed gauge must be obeyed as the
limiting factor when adjusting your engine.