ENGINE DIAGNOSTIC TEST PROCEDURES
II. AIR INDUCTION SYSTEM
The most common cause of engine failure is dirt. Even
though an air cleaner element itself is properly serviced
per the specific Operation and Maintenance Manual,
there are other areas in the induction system which
must be maintained. The importance of pressure testing
the air induction system cannot be emphasized enough
with present- day high speed diesel engines. An air
induction leak on the suction side, no matter how small,
can cause an engine failure and must not be tolerated.
Test for leakage in the air induction system using a
manually regulated compressed air supply, 0-103 kPa
(0-15 psi) pressure test gauge, tube fittings, duct tape,
paint brush and soap solution.
Block off air inlet pipe or completely mask off the
outer diameter of air cleaner element air inlet
with duct tape.
NOTE: Air systems having air cleaners with reverse
flow must be blocked at the air intake pipe.
Disconnect the air cleaner restriction indicator or
tubing at the air cleaner. Install a tee and
connect the indicator or tubing and the pressure
Remove a pipe plug from the intake manifold.
Connect the manually regulated compressed air
supply to the manifold.
Introduce air to establish that 34 kPa (5 psi)
pressurization has been achieved by reading the
pressure gauge. If improper pressure is seen,
adjust the regulator. A constant supply of air is
needed to compensate for air loss out open
Coat the following areas with the soap solution
and check for leaks. Leaks will cause air
bubbles to form.
Air cleaner body surface around the outlet
Air cleaner outlet pipe to air cleaner body
Fitting and line connection from air cleaner
outlet to restriction indicator including the
bottom of the indicator.
All clamped hose and gasket connections
between air cleaner outlet and intake
manifold. This includes connections at
turbocharger, when applicable.
Surface of all air induction piping and hoses
between air cleaner and intake manifold
including the manifold gasket area.
When applicable, the air compressor air
inlet piping from the air cleaner tube to and
including the fitting and the gasket.
No leakage is permitted between air cleaner and
turbocharger (suction side) in turbocharged
applications. If leakage at the joints is detected,
tighten hose clamps. If leakage still persists,
remove the parts to determine the cause. Re-
place parts as necessary using the latest clamps
and torques specified. Retest the corrected
NOTE: Any leaks found in air induction system
could have allowed dirt to enter engine. Dirt
entering engine can cause high oil consumption
because of badly worn or broken piston rings,
excessive blue smoke, turbocharger compressor
wheel pitting and erosion. If any leaks are found in
the air intake system, you can check the internal
condition of the engine by running a crankcase
Visually inspect the following:
damage or distortion which could allow unfiltered
air to enter the engine. Also, inspect to see that
the unloader valve is in place and not plugged by
Inspect air cleaner housing internally for damage
to baffles, end seal movement indicated by
polishing where end seal contacts the air cleaner
housing. End seal movement indicates dirt may
have passed the air cleaner element and
entered the engine.
Inspect air cleaner element for holes, damaged
seals, element sooting, end cap denting because
of overtightening or damage during servicing.
Inspect hoses and clamps for tightness and
positioning over sealing beads.
Printed in United States of America