Piper Comanche PA-24 Service Manual page 584

PIPER COMANCHE SERVICE MANUAL
7C-34A. Indlealor, Mlxlure Conlrol (EGT). The mixture control illdicator is to -
aid the pilot in selecting the most ecollomical fuel-air mixture for craisinl rulilt at a power . ,
setting of 75% or less. It is a sensinl device to monitor the fuel-air mixture leavinl the engine
cyiindm. If. after checkinl with the uouble .. booUq chart. the indicator is found to be
defective it sbould 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
leDllb of wire
u
the resistaDCe of the leads is critical for proper
operation of the gauge.
7C-34B. C1eaalnl and I
splclloa.
Ullless mechanical damase is evident. brokell
aIass.
bent
or broken pointer or brokell case. tbe foUowing cbecks sbould be performed before removing the
instrument.
a. Remove pr .... from exhaust stack alld check for broken weld (at tip end) or burnt end.
Measured resistaDCe "f probe should be .8 ohms.
b. Disconnect lead wires at illstrument and measure resistance of lead wires. Resistance
with lead wires cOllnected to probe should be 3.3 ohms.
CAUTION
Do not connect ohmmeter across meter. It will bUI1l-Gut the
movement of the meter.
c. With leads connected to instrument. heat probe with propane torch to dull red. The meter
e
should read up to the founh graduation. or approximately 1500" F. If the meter does not move. replace
it.
TROUBLE
Gauge inoperative
TABLE VlIC-IA TROLllLESHOOTlNG CHART
(MIXTURE CONTROL INDICATOR)
CAUSE REMEDY
Defective gause. probe
Check probe and lead wires
or wiring.
for chafing. breaks or
shoning between wires
and or metal struCtures.
Fluctuating reading
Loosc. frayed or broken Clean and tighten con·
POWER
PLANT
ADDED: 9/10179
electrical leads or faulty
connections.
2H2
nections. Repalf or replace
defective leads.