J.P. Instruments EDM 730 Instrument Installation Manual - Manual (Page 21)

FAA APPROVED INSTALLATION MANUAL FOR THE EGT-701 Report 103
INSTALLING THE EGT-701 SCANNER® 1/20/09
Rev-E Page 21 of 30
g) One CHT reads higher or lower than the others. It is most likely that this is the cylinder that has the
spark plug gasket probe installed. Choose the upper or lower spark plug, the one that provides the best
correlation with the other temperature probes. Due to the spark plug location, the gasket probe may
read higher or lower than the factory probe. Place the probe on the plug that receives the most direct
cooling air
h) One cylinder seems to read erroneously. Physically swap the suspected probe with a probe from a
correctly reading cylinder. If the problem moves to the correctly reading cylinder (stays in the same
column on the instrument) check the crimps between the probe and the wiring harness. Check the pins
on the connector that plugs into the instrument. If those check okay, then the probe should be replaced.
If the problem moves to the other probe’s column on the instrument, the temperature readings are
correct and there is probably a problem with the original cylinder.
i) Large EGT span. Normally aspirated (carburetor) engines at normal cruise display a “DIF” of 125 to
175 o F spread between cylinders. Injected engines at normal cruise display a “DIF” 50 to 90 o F spread
between cylinders. All cylinders are measured by common circuitry. It is unlikely that the calibration is in
error on only one channel.
j) Temperature reading varies more than 500°F in one second. Check for a poor quality crimp between
the probe and harness.
k) All EGT or CHT readings seem too high or low or unsteady. Verify that the Instrument is grounded
at the engine block for single engine installations. Use a DVM (digital voltmeter) to measure the
difference between instrument ground and the engine block ground. If the difference is greater than 0.5
volts with the alternator charging, the ground to the instrument is faulty.
l) All EGT and CHT readings seem too low. The instrument may be set to display engine temperatures
in Celsius when you are used to seeing Fahrenheit. See Pilot’s Guide under Pilot Programming.
m) OAT readings in error more than 10°, but oil and CHT readings are okay. Look for copper wire spliced
in line to the OAT probe. The OAT reading can be adjusted
10°. See Pilot’s Guide under Pilot
Programming.
n) All CHTs read high (100F) EGT-701 calibrated for Gem installation “J” calibration. Change to “K”
calibration using the procedure to set alarm limits described earlier.