Electronics International CA-1 - Manual (Page 8)

5
EGT's Operating Information
you approach peak, the exhaust gas temperature will rise much slower until it starts to decrease. When
this happens you have reached peak EGT. The 1`F resolution of the digital display will be invaluable in
helping you precisely detect peak EGT.
C. Finding The Cylinder That Peaks First: For most engines Step B (Precision Leaning) will result in a
properly leaned engine. If you find this to be the case with your engine, this step will not be necessary.
But if you want to verify that you have leaned to the cylinder that peaked first and your engine is
operating properly, perform the following with the cylinder found in step B at peak EGT. Slightly
enrich the mixture and quickly step through each cylinder. Any cylinder that shows a rising temperature
is a leaner cylinder. Check that this cylinder does not rise more than 15’F before it starts decreasing in
temperature. If a cylinder rises more than 15’F it may have a problem.
When installing a single channel EGT instrument in an aircraft there is no guarantee that the probe is in-
stalled on the leanest cylinder. Every engine operates a little differently. For the same make and model of
engine installed in the same type of aircraft there can be differences between the leanest cylinders. Further-
more, there can be a difference between operating temperatures and the temperature spread between cylin-
ders. Every engine has its own unique operating temperatures. To properly lean your engine using a single
channel EGT unit perform the following steps:
A. Rough Leaning: Adjust the mixture control from the full rich position to a leaner setting that results
in a slight drop in engine RPM or to a setting near peak EGT, as dictated by experience. The mixture
control should be left at this setting until the EGT’s stabilize. It will take about 20 seconds for the
temperatures to stabilize within 1`F. This lag is due to the combustion walls and piston domes increas-
ing in temperature and, therefore, affecting the combustion and exhaust gas temperatures. To correctly
lean an engine you must wait for the engine to thermally stabilize. Less sensitive gauges will not pick
up these subtle changes, which are important in leaning and diagnosing problems.
B. Precision Leaning: Again, start leaning, making only very small adjustments and waiting 3 to 5
seconds between adjustments. As you approach peak the exhaust gas temperature will rise much slower
until it starts to decrease. When this happens you have reached peak EGT. The 1`F resolution of the
digital display will be invaluable in helping you precisely detect peak EGT. You will then need to
enrichen the mixture for an EGT reading 30 'F lower than peak to insure there is no cylinder operating
on the lean side of peak EGT.
If your engine runs rough before peak EGT is reached, note the temperature reading on the EGT
instrument. When an engine starts to run rough (not when it loses power, but actually runs rough) the
leanest cylinder has gone past peak EGT by 30 to 50 degrees F. The leanest cylinder is lean misfiring
causing the engine to run rough. From this point enrichen the mixture to obtain a 50 degrees F lower
EGT from the noted temperature. This will set the leanest cylinder slightly on the rich side of peak
EGT. The rest of the cylinders will be running richer than the leanest by an amount dictated by the
temperature spread for your engine. With this method you can reasonably lean an engine even when the
probe has not been mounted on the leanest cylinder.
Electronics International's unique stable display allows you to precisely lean to peak EGT or to a specific
temperature below peak for most engines. Peak EGT with a float-type carbureted engine is frequently a
vague point because of the fuel/air distribution issues in these lower horsepower engines. As a result, these