J.P. Instruments EDM 930 Primary Pilots Guide - Manual (Page 33)

For Your Safe Flight Page 28
Expanded Leaning Procedures
Lean Of Peak mode: During the ‘lean of peak’ process, the EDM hunts
for the last cylinder to peak. 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 beyond 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 column will flash and
RICHEST appears . The digital readout
will show the current temperature difference from where peak EGT
occurred and the current fuel flow (if so equipped). Note: holding the
PEAK button will show the captured peak value of the ‘last EGT to
peak’ and also the difference in fuel flow between the first and last to
peak (known as the GAMI Spread). This is a good indication of injector
balance (the smaller the FF difference, the better the 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 (typically 1650°F to 1750°F) may limit the leaning
process, depending on flight conditions. 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. NOTE: TIT can read
approximately 100°F hotter than the hottest EGT due to 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.