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YO-233-B2A Engine Maintenance Manual
TEO-540-A1A Engine Maintenance Manual
Problem
Engine will not idle
unless the boost pump
is on (Cont.)
Engine will not shut
off
Low fuel flow
Carburetor shut-off
© 2021 Avco Corporation. All Rights Reserved
February 2021
Table 1 (Cont.)
Fault Isolation Guide
Cause
Low fuel pressure
Very lean idle mixture
Pressure too low at idle
speed (engine could also
lose fuel pressure as the
aircraft climbs)
Idle mixture is extremely
rich (evident by excess
black exhaust)
Fuel pressure is set too
high
Broken fuel pump drive
Faulty power switches
Faulty wiring in the
harness
Ignition switch faulty
Dirty fuel filter
Faulty power switches
Faulty wiring in the
harness
Ignition switch faulty
Corrective Action
Replace fuel pump.
1. Enrich idle mixture. Refer
to instructions in the
section "Idle Speed
Mixture Adjustment" in
Chapter 72-00.
2. Readjust idle speed.
Look for loose fuel fitting.
Tighten loose fuel fitting.
1. Lean idle mixture. Refer to
instructions in the section
"Idle Speed Mixture
Adjustment" in Chapter
72-00.
2. Readjust idle speed.
Adjust engine fuel pump.
Replace the fuel pump in
accordance with airframe
manufacturer's instructions.
Replace the switches.
Replace the harness.
Check for faults on the ignition
switch circuits. Repair as
necessary.
Remove and replace the fuel
filter.
Replace the switches.
Replace the harness.
Check for faults on the ignition
switch circuits. Repair as
necessary.
Ref.
OHM
72-00
72-00
OHM
12-30
Page 77
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