Piper COMANCHE PA-24-180 Service Manual page 456

PIPER COMANCHE SERVICE MANUAL
7C-34A. Indicator, Mixture Control (EGT). The mixture control indicator is to
aid the pilot in selecting the most economical fuel-air mixture for cruising flight at a power
setting of 75% or less. It is a sensing device to monitor the fuel-air mixture leaving the engine
cylinders. If. after checking with the trouble-shooting chart. the indicator is found to be
defective it should be replaced. If the leads are found to be defective they should be replaced.
NOTE
When replacing leads it is important to use the same type and
length of wire as the resistance of the leads is critical for proper
operation of the gauge.
7C-34B. Cleanig and Inp cti.
Unless mechanical damage is evident. broken glass, bent
or broken pointer or broken case the following checks should be performed before removing the
instrument.
a. Remove prtn from exhaust stack and check for broken weld (at tip end) or burnt end.
Measured resistance uf probe should be .8 ohms.
b. Disconnect lead wires at instrument and measure resistance of lead wires. Resistance
with lead wires connected to probe should be 3.3 ohms.
CAUTION
Do not connect ohmmeter across meter. It will burn-out the
movement of the meter.
c. With leads connected to instrument. heat probe with propane torch to dull red. The meter
should read up to the fourth graduation. or approximately 15000 F. If the meter does not move, replace
it.
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TABLE VIIC-IA TROUBLESHOOTING CHART
(MIXTURE CONTROL INDICATOR)
TROUBLE CAUSE REMEDY
Gauge inoperative
Fluctuating reading
Defective gauge. probe
or wiring.
Loose, frayed or broken
electrical leads or faulty
connections.
Check probe and lead wires
for chafing. breaks or
shorting between wires
and or metal structures.
Clean and tighten con-
nections. Repair or replace
defective leads.
POWERPLANT
ADDED: 9/10/79
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