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 2)  Remove the bolts and washers which hold the main fuel supply line and the bracket to the engine fuel pump.
 3)  Disconnect the main engine supply line from the engine fuel
 pump.
 4)  Remove the gasket.
 5)  If the gasket has no damage, keep it for the installation.
 6)  At engines No. 2, 3 and 4, install a cap on the open end of
 the main fuel supply line. 7) Do these steps at the No. 1 engine: a) Connect the pressure check equipment (Fig. 601) to the open end of the main fuel supply line. b) Connect the air pressure source to the pressure check equipment.
 S 866-009
 (6)  
Make sure the all of the manual refuel valves and defuel valves are in the CLOSED position.

 S 986-010

 (7)  
Use the manual lever to open all the engine fuel shutoff and crossfeed valves.

 S 986-011

 (8)
Use the manual lever to close the fuel shutoff valve on the APU.

 F.  
Procedure

 S 786-012
 (1)  
Use the air pressure source to apply 40 psig to the inlet line of the fuel pump.

 (2)
Close the shutoff valve on the pressure check equipment (Fig. 601).

 S 216-014

 (3)  
Monitor the pressure gage for 10 minutes.

 (a)  
If the pressure stays the same or the pressure decreases by less than 1.5 psi in 10 minutes, the system is satisfactory.

 (b)  
If the system is satisfactory, remove the pressure check equipment and put the aircraft back to the serviceable condition.

 (c)  
If the pressure decreases more than 1.5 psi or more in 10 minutes, there is a leak in the engine fuel-feed line. 1) Open the shutoff valve on the pressure check equipment.

 S 866-013
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747-400
MAINTENANCE MANUAL

 

REGULATOR WHICH CAN DECREASE AIR PRESSURE TO 40 PSIG.
Pressure Check Equipment Figure 602
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747-400 MAINTENANCE MANUAL
 2)  Do step (4) to isolate the leak.
 S 796-015
 (4)  
Do these steps to isolate the leak in the engine fuel-feed line.

 (a)  
Use the air pressure source to apply 40 psig air pressure to the inlet line of the fuel pump.

 (b)  
Close the shutoff valve to the No. 4 engine (the valve the farthest from the pressure source).

 (c)  
Close the shutoff valve on the pressure check equipment.

 (d)  
Monitor the pressure gage for 10 minutes.

 (e)  
The leak is downstream of the shutoff valve to the No. 4 engine if the pressure during the test is as follows: 1) The pressure stays the same for 10 minutes. 2) The pressure decreases less than 1.5 psi in 10 minutes.

 a)  If the leak is downstream of the last valve closed, do a check for air leaks on the fuel-feed lines and couplings.
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747-400 MAINTENANCE MANUAL
 (f)  
If the pressure decreases more than 1.5 psi or more in 10 minutes, open the shutoff valve on the pressure check equipment.

 (g)  
Do a check of the valves, in the sequence that follows, to isolate the leak.

 NOTE: You must only do one valve at a time.
____
 -
No. 4 fuel crossfeed

 -
No. 3 engine fuel shutoff

 -
　
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