J.P. Instruments EDM 700/800/711 Pilots Guide - Manual (Page 26)

Page 22 Engine Data Management
Engine Diagnosis Chart
The following chart will help you diagnose engine problems in your
aircraft. (Views are Percentage views). Notice that there will be always
one CHT that is shown hotter than the others.
Display Symptom Probable Cause Recommended
Action
CHT
300
400
500
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.
CHT
300
400
500
EGT Increase
or decrease
after ignition
system
maintenance Improper timing:
high EGT

retarded ignition;
low EGT

advanced ignition.
Check EGT for
each magneto to
determine any
uneven timing.
CHT
300
400
500
Loss of EGT
for one
cylinder.
Engine rough Stuck valve. Other
cylinders are okay. Have valve train
checked.
CHT
300
400
500
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.
CHT
300
400
500
Decrease in
EGT for one
cylinder Intake valve not
opening fully; faulty
valve lifter. Have valve lifter or
rocker arm
checked.
CHT
300
400
500
Decrease in
EGT for one
cylinder at low
RPM Low compression. Check
compression.