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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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
F11457
////////////////////////A / GTCP85-129 SERIES /737-300/400/500/ ENGINES /MAINTENANCE MANUAL ////////////////////////
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.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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 49-00-00
 PART NUMBER 3876259  ú
 ú  02  Page 161
 ú  Jul 12/01 

BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
L38637
////////////////////////A / GTCP85-129 SERIES /737-300/400/500/ ENGINES /MAINTENANCE MANUAL ////////////////////////
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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