J.P. Instruments Classic Scanner - Manual (Page 8)

INSTALLING THE EGT SCANNER
Page 8 of 8
Rev-D
23) Trouble Shooting
• EGT, large span.
Aspirated (carburetor) engines at normal cruise display a 100 to 175 o F spread
between cyls. Injected engines at normal cruise display 50 to 80 o F spread between
cylinders. All cylinders are measured by a common circuitry. It is almost impossible
to not have identical calibration on all channels.
• Having problems with one cylinder reading ?
Swap probe with a good cylinder probe. If the problem goes to the good cylinder the
probe should be replaced. If the problem remains the same, it is in the hookup wiring
at the instrument. Look for strands from one lead shorting to the next terminal. Look
for the wire to be shorting to the airframe.
• Using an Ohm meter or continuity checker measure across the probe output leads.
A good probe should be low ohms (2 ohms).
• A dot (.) in the temperature display (over 1000 F) after the first digit like 1.370 F
means the hookup wire leads are reverse polarity (Red/Yellow) at the instrument or
probe.
• A steady reading of 90 to 170 F on only one cylinder indicates the probe is not
connected or it is open.
• If the temperature is changing more than 500 F in one second it should not be
trusted and a lose wire crimp or probe should be suspected.
• EGT or CHT readings seem to High or Low or Unsteady. Use a DVM (digital
voltmeter) to measure the difference between SCANNER ground and the engine
block ground. If the difference is greater than 0.5 volts with the alternator charging.
Then remove the SCANNER ground (Black wire) from the instrument panel and
connect it directly to the ENGINE BLOCK for GROUND.
• CHT REVERSE POLARITY will show up in the Display by causing the small "c" to
change to a small "o". Check TC wire color code. When the engine is first started the
CHT temperatures will go down to zero and then start up.
• Make sure the Instrument is grounded at the engine for single engine installations