Troubleshooting the APU When Engine Starts But Fails To Keep Running.
This portion of the subcourse teaches the troubleshooting steps used to
determine why the APU engine will not continue to run after starting.
However, before you apply the troubleshooting steps, it is essential that
you make a thorough check of the engine air cleaner and fuel systems, i.e.,
air cleaner filter element and hoses for restrictions, the fuel supply lines
for damage or restrictions, and the fuel filters for restrictions, clogging,
Remember, the necessary ingredients for the engine to
operate properly are air, fuel, and ignition, provided in the proper
When you have completed the preliminary checks and the cause for the
engine's failure to continue operating has not been determined, then the
following troubleshooting procedures must be applied:
Set the MASTER switch to the OFF position. Find terminal D, lead
487, in the APU harness plug (Figure 22).
Probe through the
insulation of lead 487 wire with the multimeter red probe and
ground the black probe.
Set the MASTER switch to the ON
If no voltage was indicated by this test, then lead
487 from the preheat solenoid terminal 487 to the APU harness
plug requires repair or replacement.
Refer to TM 9-2350-267-20
for procedures used to repair or replace lead 487.
If voltage is indicated during this test, proceed to the next required test
Set the MASTER switch to the OFF position.
Remove the APU
control box, using the procedures outlined in TM 9-2350-267-20,
but DO NOT disconnect the control box harness.
control box connector lead 487 terminal A (Figure 23).
through the insulation of terminal A wire 487 with the multimeter
red probe and then ground the black probe. Set the MASTER switch
to the ON position.
If no voltage is indicated by this test,
lead 487 from the APU compartment connector to the APU control
box requires repair or replacement.
Accomplish repair or
replacement as outlined in TM 9-2350-267-20.