Why Measure Temperature? An old and common misconception that other manufacturers of EGT monitors promote is that it is not necessary to know the exact exhaust gas temperatures of your aircraft's engine. However, if you have read recent reports, shock cooling can be catastrophic! The EDM alerts the pilot of those conditions which are most vital to the maintenance of well performing engine. The value in measuring EGT lies in finding the ideal ratio of fuel to air that results in complete combustion, and in long-term trend monitoring.
Long Term trend Monitoring: Trend monitoring will identify thosesmall problems before they turn into serious engine damage. It is the most important tool for diagnosing engine problems, and it works! Digital displays make all the difference obvious. Trend monitoring is simply not possible with just a bar graph indicator. Yet, with only a digital indicator, quick glance temperature recognition is not possible either. With a digital display, engine data can be recorded by the pilot in a log book on a monthly basis. EGT and CHT will group themselves into a tight pattern at specific MAP & RPM. As a problem begins to develop in one or more cylinders, the EGT span will start to enlarge. The DIFF mode "dot" will identify the problem cylinder causing the large span. Factory new injected engines have a typical span of 80ºF, carburated 140ºF.
Leanfind Mode: The EDM-700 identifies the optimum mixture accurately and automatically. After cruise power has been established, the pilot just presses the function button of the LEANFIND "LF" mode. As the pilot begins to lean the mixture, the EDM-700 is checking all cylinders, using a propriety algorithm looking for the first cylinder to achieve peak EGT. "PEAK EGT" will be displayed when the first cylinder to peak is detected. The display will also then flash the cylinder column and show peak EGT. The pilot has the option to increase (the richness of the mixture) or operate at peak. Leaning faster than the engine can respond will cause the display to flash "2 FAST." The EDM is monitoring all alarms in the background and if the TIT limit is exceeded during the Lean Find process, the TIT column will flash first. Some turbocharged engines do peak TIT before the EGT peaks.
Since 1995, pre-ignition and detonation have become more prevalent with the new fuels available. Therefore it is of the utmost importance to monitor ALL EGT's at one time during climbing, and leaning. Pre-ignition once started, causes an extreme temperature rise and is self sustaining until engine failure occurs, which can be in less than one minute. Pre-ignition will cause the EDM's bar graph to reach maximum height on that cylinder. Seeing all cylinders at once will permit the immediate action required by the pilot.
Lean Find Mode—“Lean of Peak” LOP
To use the “lean of peak” method, tap LF and then immediately hold both Exit and RoP/LoP until you see LeanL. You may toggle back to LeanR by holding both buttons again. Once you begin leaning (blinking square) you cannot change leaning method. Upon power up, the EDM 700/800 always defaults to Rich of Peak mode.
Leaning Lean of Peak (LOP)
In the “lean of peak” method the columns will invert with the first to peak progressing down from the top of the display, looking like icicles. The “icicle” scale has higher sensitivity. As you continue to lean past peak the number of the each successive cylinder will blink as it peaks. The peaks will be shown as an icicle graph; when the last cylinder peaks its column will blink. The analog display is an icicle graph showing where each cylinder peaked. When the RoP/LoP button is held the display will show the delta fuel flow between the first and last to peak (GAMI Spread), as well as the richest peak EGT.
The leaning process for turbocharged engines is by reference to the first cylinder or TIT to reach peak. However, the TIT factory red line may limit the leaning process. TIT red line is generally 1650°F, and up to 1750°F in some installations. In the LeanFind mode the T column—TIT—is included in the procedure. If during leaning the TIT exceeds red line by less than 100° for less than one minute, the LeanFind procedure will continue to operate, allowing you to complete the leaning process. Otherwise the digital display will show, for example, 1650 TIT and TIT will blink. You may notice that in some cases the TIT reads 100°F hotter than the hottest EGT.
Consider Economics: For example, a Beech Bonanza with an 0-470 engine at 10,000 ft. @ 65% power and fuel at $4.20 per gal. At a true airspeed of 160 mph and at PEAK EGT, this engine consumes 11 GPH. This means that if you fly 500 hours a year, the Bonanza will consume $23,100 in fuel.
Most pilots not knowing which cylinder peaks first, operate at a 75 to 100 degrees rich of peak. Too rich of a condition causes vibration and carbon deposits in the engine. Flying under such conditions, a very rich mixture would result in an increase airspeed of 2 mph, while the fuel burned would increase by 2.2 GPH. If the EDM was used to lean the engine only 10 degrees rich of the peak, the plane would cost 20% less to operate or $4620. Again if you are injected and run LOP (Lean of Peak) by 50 degrees you could save 30% in fuel or $6930 a year and lose 2 Kts.
Data Recorder: A complete engine data recording system. Capable of recording not only EGT and CHT as some less sophisticated systems do, but also can record all 24 engine temperatures, plus all engine pressures, RPM and can calculate percent of horsepower. The ability to print out alarm conditions, with three dimensional color data analysis of your computer, is also a feature.
Additional Functions Required for Automatic Data Recording: Diagnosing an engine problem is a very complex task, requiring the data from several engine instruments. Recording EGT & TIT temperatures is only the start. In order to fully understand the engine, RPM, MAP, OIL TEMP., are also required. This is why you should not be misled by less sophisticated copies that claim data recording capabilities. These gauges simply don't record the necessary information to make a thorough engine problem diagnosis. For example, a large drop in EGT could be a serious problem developing or just the addition of full throttle. JPI realized this at the beginning of the development of its EDM data recorder.
Percent of Horsepower: JPI's proprietary algorithm calculates and displays percent of horsepower from carburated, normally aspirated, high performance injected, turbocharged and inter cooled engines. Try taking off from a high density altitude airport by setting maximum HP before releasing the brakes.