FUEL FEED LOW PRESSURE INDICATING SYSTEM -TROUBLE SHOOTING
1.  General
A.  Trouble shooting the fuel feed low pressure indicating system consists of the isolation of any circuit faults to determine which component should be replaced or which wire should be repaired.
2.  Fuel Feed Low Pressure Indicating System Trouble Shooting Chart
A.  Make sure there is a minimum of 2000 pounds (900 kilograms) of fuel in each tank.
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FUEL FEED LOW PRESSURE INDICATING SYSTEM - ADJUSTMENT/TEST
1.  Fuel Feed Low Pressure Indicating System Test
A.  General
(1)  Testing the fuel feed low pressure indicating system requires that each fuel tank contain fuel. The low pressure indicating system test is a portion of the engine fuel feed system test; if the fuel feed system test is being done, it is not necessary to do a separate test of the low pressure indicating system.
B.  Test of the Fuel Feed Low Pressure Indicating System
(1)  
Make sure that all fuel boost pump switches on the overhead panel are in the OFF position.

(a) Make sure each tank has a minimum of 2000 pounds (900 kilograms) of fuel.

(2)  
Connect electrical power to the airplane.

(3)  
Make sure that all boost pump and pump low pressure circuit breakers, on the P6-3 panel, are closed.

(4)  
Make sure the tank No. 1 and 2 boost pump low pressure indicating lights, on the forward overhead panel, are on.

(5)  
Press-to-test the center tank boost pump low pressure indicating lights.

(a)  Make sure the bulbs come on.

(6)  
Pull the engine fire switches, on aft electronic panel (P8-1), to FIRE position to close the engine fuel shutoff valves.

(7)  
Make sure the APU master switch, on forward overhead panel, is in OFF position.

(8)  
Make sure the crossfeed valve switch, on forward overhead panel, is in CLOSED position.

(9)  
Make sure the manual defueling valve is closed.

(10)
Put the tank No. 1 forward boost pump switch in ON position.

(a)  To operate any of the fuel boost pumps, you must be in the flight compartment to continuously monitor the fuel quantity and the low pressure indication in the fuel tank.
WARNING:  DO NOT OPERATE ANY FUEL BOOST PUMP IF THE LOW PRESSURE LIGHT COMES ON AND STAYS ON. FUEL VAPORS IN THE TANK MAY IGNITE AND CAUSE A FIRE OR EXPLOSION.
1)  Immediately put the applicable fuel boost pump switch(es) to OFF if the LOW PRESSURE light comes on and stays on.
NOTE:  When defueling or transferring fuel with minimum backpressure to the pumps, it is possible for the low pressure light(s) to be on.  In this case, monitor the tank quantity and put the pump switch(es) to OFF if the tank quantity is not changing.
(11)
When the fuel pressure has built up, make sure the pump low pressure indicating light goes off.

(12)
Make sure there is no fuel leakage at the pressure switch.

(13)
When the pump low pressure indicating light goes off, put the boost pump switch to OFF position.

(14)
Repeat steps (10) through (13) for the three remaining tank No. 1 and 2 fuel boost pumps.

(15)
Open the RH center tank fuel boost pump circuit breaker, on P6-3 panel.

(16)
Put the R CTR tank fuel boost pump switch in the ON position.

(17)
Make sure the pump low pressure indicating light comes on.

(18)
Close the RH center tank fuel boost pump circuit breaker.

(19)
When the fuel pressure has built up, make sure the pump low pressure indicating light goes off.

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(a)  To operate any of the fuel boost pumps, you must be in the flight compartment to continuously monitor the fuel quantity and the low pressure indication in the fuel tank.
WARNING:  DO NOT OPERATE ANY FUEL BOOST PUMP IF THE LOW PRESSURE LIGHT COMES ON AND STAYS ON. FUEL VAPORS IN THE TANK MAY IGNITE AND CAUSE A FIRE OR EXPLOSION.
　
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