EMS Monitoring Functions
EMS-D10 Pilot’s User Guide
6-3
Pre-ignition Characteristics
Pre-ignition manifests itself as high EGT and high CHT temperatures resulting from premature ignition of fuel/air
mixture in advance of normal ignition. This is usually caused by a hot spot in a combustion chamber. A hot spot is
typically the spark plug electrode or exhaust valve. When pre-ignition occurs, ignition timing is lost and the upward
movement of the piston is opposed by the high pressure generated by the early combustion.
Ignition Misfire
When a magneto fails or a plug gets fouled, one of the plugs in the cylinder stops firing. This causes the fuel to burn
slower than it usually does, since only one plug ignites the mixture. This slow burn means some unburned fuel makes its
way into the exhaust stack and burns there, causing high EGT values. This also means less energy is being put into the
head, so the CHTs will also fall. If it occurs on one cylinder, suspect a fouled plug and try clearing it out. If it occurs on
all cylinders at once, suspect a magneto and take appropriate action for your aircraft.
Shock Cooling
Significantly reducing power and dropping the nose simultaneously can cause shock cooling. This can cause the engine
to cool rapidly and unevenly. When this happens, the rear of the engine is exposed to less cooling air than the front of the
engine. Shock cooling is characterized by rapidly dropping and uneven CHT temperatures and may lead to cylinder
cracking. You may configure shock cooling and span alarms; see the EMS-D10 Installation Guide for more details.
Data Logging
While many observations can be made via the various indicators on the EMS Main Page, some patterns are too subtle to
be noticed during routine flight. Logging engine data over longer periods of operation allows you to spot potential
