J.P. Instruments EDM 900 Pilots Guide - Manual (Page 15)

For Your Safe Flight Page 15
Engine Diagnosis Chart
The following chart will help you diagnose engine problems in your
aircraft.
Display Symptom Probable
Cause
Recommende
d Action
TIT ~100°
higher than
EGTs This is normal
75° to 100°
EGT rise for
one cylinder
during flight Spark plug not
firing due to fouling,
faulty plug, wire or
distributor. Enrich mixture to
return EGT to
normal. Have
plugs checked.
EGT Increase
or decrease
after ignition
maintenance Improper timing:
high EGT

retarded ignition;
low EGT

advanced ignition.
Check EGT for
each magneto to
determine any
uneven timing.
Loss of EGT
for one
cylinder.
Engine rough Stuck valve. Other
cylinders are okay. Have valve train
checked.
Loss of EGT
for one
cylinder; no
digital EGT Failed probe
or
failed wire harness. Swap probes to
determine if probe
or wire harness is
bad.
Decrease in
EGT for one
cylinder Intake valve not
opening fully; faulty
valve lifter. Have valve lifter or
rocker arm
checked.
Increase in
DIF at low
RPM Low compression
(blow by) in
cylinder Check
compression.
EGT and
CHT not
uniform Normal for
carbureted
engines. Dirty fuel
injectors or fouled
plugs. Check injectors
and plugs.
Decrease in
EGT for all
cylinders Decrease in airflow
into the induction
system. Carb or
induction ice. Check for change
in manifold
pressure.