35 REPLACE THE LOW-PRESSURE
FUEL FILTER (AMM 49-31-21/401)
AND CLEAN THE HIGH-PRESSURE
FUEL FILTER (AMM 49-31-81/
301).
DOES THE PROBLEM CONTINUE?
YES
NO
36 EXAMINE THE CIRCUIT FROM
THE FUEL SOLENOID VALVE,
CONNECTOR D1264, PIN B, TO THE
SEQUENCING SWITCH FOR THE OIL
PRESSURE, CONNECTOR D1250,
PIN 4 (WDM 49-31-01).
IS THE CIRCUIT OK?
YES
SEE SHEET 8 (BLOCK 37)
Starter Motor Turns the APU Engine but There Is No Combustion (No Increase in EGT)
Figure 113 (Sheet 7)
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PART NUMBER 305593 ú
ú 02 Page 159
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FROM SHEET 7 (BLOCK 36)
YES
NO
37 MEASURE THE RESISTANCE AT
THE FUEL SOLENOID VALVE,
CONNECTOR D1264, FROM PIN A
TO PIN B (WDM 49-31-01).
IS THE RESISTANCE 20-45 OHMS?
GROUND (WDM 49-31-01). IS THE CIRCUIT OK?
YES
Starter Motor Turns the APU Engine but There Is No Combustion (No Increase in EGT)
Figure 113 (Sheet 8)
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ú 02 Page 160
ú Jul 12/01
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
F11459
STARTER MOTOR TURNS PREREQUISITES
THE APU ENGINE BUT MAKE SURE THIS SYSTEM WILL OPERATE:
THERE IS NO COMBUS- APU (AMM 49-11-00/201)
TION (NO INCREASE MAKE SURE THE AIRPLANE IS IN THIS CONFIGURATION:
IN EGT) ELECTRICAL POWER IS ON (AMM 24-22-00/201)
POSSIBLE CAUSES:
1.
IGNITION SYSTEM: . IGNITER PLUG PROBLEM (AMM 49-41-51/401) . IGNITION UNIT PROBLEM (AMM 49-41-31/401) . IGNITER CABLE PROBLEM.
2.
FUEL SYSTEM: . APU FUEL VALVE, V43, PROBLEM (AMM 28-22-31/401) . FUEL TUBE DAMAGE OR LEAKAGE . FUEL SOLENOID VALVE PROBLEM (AMM 49-31-31/401) . FUEL CONTROL UNIT PROBLEM (AMM 49-31-11/401) . CLOGGED FILTER FOR THE LOW-PRESSURE FUEL (AMM 49-31-21/401) . CLOGGED FILTER FOR THE HIGH-PRESSURE FUEL (AMM 49-31-81/301) . COMBUSTOR UNIT PROBLEM (AMM 49-31-42/401).
3.
OIL PUMP PROBLEM (AMM 49-91-11/401)
4.
THE SEQUENCING SWITCH FOR THE OIL PRESSURE PROBLEM (AMM 49-61-41/401)
5.
ELECTRONIC SPEED SWITCH, S634, PROBLEM (AMM 49-61-22/401)
6.
APU CONTROL UNIT, M280, PROBLEM (AMM 49-61-11/401).
FAULT ISOLATION:
YES SEE SHEET 4
1 DO THE APU DRY MOTORING
(BLOCK 9)
(AMM 49-11-00/201). LISTEN FOR THE NORMAL
SOUND OF THE IGNITION SYSTEM. DO YOU HEAR THE NORMALSOUND OF THE IGNITION SYSTEM?
NO NO
2 EXAMINE THE IGNITER PLUG
(AMM 49-41-51/601).
IS THE IGNITER PLUG IN
GOOD CONDITION?
YES SEE SHEET 2
(BLOCK 3)
Starter Motor Turns the APU Engine but There Is No Combustion (No Increase in EGT)
Figure 113A (Sheet 1)
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PART NUMBER 3876259 ú
ú 02 Page 161
ú Jul 12/01
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
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FROM SHEET 1 (BLOCK 2)
FROM THE IGNITION UNIT. START THE APU (AMM 49-11-00/201).
NOTE: WITH THE CONNECTOR DISCONNECTED FROM THE IGNITION UNIT, THE APU WILL NOT START.
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