Electronics International TC-1P - Manual (Page 8)

5
TIT Operating Information
2. Using the TIT Instrument to Lean Your Engine:
You will want to lean your engine in cruise. A rich running engine wastes fuel needlessly and tends to run
on the rough side. This create vibration, which causes deterioration of engine accessories and engine
mounts. Also, proper leaning at cruise and during descent means less spark plug fouling, longer life for the
plugs, reduced maintenance costs and considerable fuel savings. Furthermore, good leaning techniques
result in cleaner combustion chambers with fewer lead salt deposits on the pistons and exhaust valves. Under
certain conditions, these deposits invite preignition and higher maintenance costs. Proper leaning at cruise
during cool or cold weather aids in raising engine and oil temperatures to desirable minimums in order to
evaporate the water and acids out of the oil. Water and acids attack the insides of an engine, causing rust and
corrosion.
The TIT is a collection of the EGT's for all the cylinders. As you lean the engine, one cylinder will reach
peak EGT before the others. As you continue to lean, the EGT for the leanest cylinder will decrease in
temperature but the TIT will continue to increase. When the combined total of all the increasing cylinders
equals all the decreasing cylinders, the TIT will reach peak. For this reason, using a TIT to lean an engine is
not as desirable as using a multi-channel EGT instrument. But, if you must lean the engine using only the
TIT, 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 TIT, as dictated by experience. The mixture
control should be left at this setting until the TIT stabilizes. It will take about 20 seconds for the tem-
peratures to stabilize within 1`F. This lag is due to the combustion walls and piston domes increasing in
temperature, which affect the combustion and exhaust gas temperatures. To correctly lean an engine
you must wait for the engine to thermally stabilize. Less sensitive instruments 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 TIT. The 1`F resolution of
the digital display will be invaluable in helping you precisely detect peak TIT. If your engine runs
rough before peak TIT is reached, note the temperature reading on the TIT 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 TIT 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 dectated by the temperature spread for your engine. With
this method you can reasonably lean an engine with the TIT instrument.
For your engine, check the engine manufacturer’s recommended leaning procedures. It is not recom-
mended to lean near peak TIT for power settings above 75%. The richer mixture is needed to cool the
combustion temperatures and keep the anti-knock capability of the fuel high enough to prevent detonation
from occurring at the higher power settings.