Lycoming YO-233-B2A - Page 97

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