Service Manual

ISB, ISBe and QSB (Common Rail [...] Crankcase Blowby, Measure
Section 14 - Engine Testing - Group 14 Page 14-45
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WARNING
Wear appropriate eye and face protection when using
compressed air. Flying debris and dirt can cause
personal injury.
Air Compressor Blowby Contribution:
With the engine blowby service tool and the water
manometer, pressure gauge, or transducer still installed,
isolate the air compressor, if equipped, to determine if
there is internal damage to the air compressor
contributing to high engine crankcase pressure. The air
compressor can be isolated by unloading the air
compressor.
With the engine shut off, bleed the vehicle's air system
down by opening the drain cock on the wet tank to release
compressed air from the system.
NOTE: The air compressor governor/unloader location
can vary on each engine application. The air governor/
unloader can be air compressor mounted or chassis
mounted.
Disconnect the air signal line from the air compressor
governor/unloader air signal port.
Disconnect the air compressor discharge line and air
intake hose from the air compressor.
NOTE: On turbocharged air compressors, make sure to
plug the air intake hose connected to the engine intake
manifold or the engine will not reach full power during
test.
To unload the air compressor, determine the pressure
needed at the governor/unloader air signal port to start
and stop the air compressor from pumping.
NOTE: Typical 621 kPa [90 psi] of air pressure is the set
point between starting and stopping of the air compressor
pumping. Refer to the OEM service manual.
Connect a regulated shop air pressure line, with pressure
gauge, to the air compressor governor/unloader air signal
port.
NOTE: When performing the test, make sure that the air
system pressure does not exceed the manufacturer's
maximum allowable pressure.
Run the engine and increase the signal pressure to the air
governor/unloader to determine when the air compressor
will stop pumping (system pressure stops rising at this
point). Record the signal line pressure.
Reduce the signal pressure to determine when system
pressure starts the air compressor pumping again (system
pressure will begin to rise again at this point). Record the
signal line pressure.
NOTE: Allow the air compressor to pump long enough to
build enough pressure in the system to release and
operate the air brakes.