TM 5-3895-383-24
b.
Air inlet piping damage or restriction:
Make a visual inspection of the air inlet system and
check for damage to piping, rags in the inlet piping,
or damage to the rain cap or the cap is pushed too
far onto the inlet pipe. If no damage is seen,
check the inlet restriction with a clean air cleaner
element.
c.
Turbocharger not operating properly:
Check turbocharger for proper operation.
d.
Engine used in a lug condition:
"Lugging" (when a load is too great for the engine
rpm to increase as the throttle is moved to full fuel)
the engine causes a reduction in the intake of air
with full fuel delivery to the cylinders. Because
there is not enough air to burn all the fuel, the fuel
that is not used comes out of the exhaust as black
smoke. To prevent "lugging" the engine, lessen the
load to where the engine can have "acceleration"
(increase in rpm) under load.
3.
Exhaust system restriction:
Make a visual inspection of the air inlet system and
check for damage to piping or a defective muffler. If
no damage is found, check the system by checking
the back pressure from the exhaust (pressure
difference measurement between exhaust outlet and
atmosphere). The back pressure must not be more
than 1016 mm (40 in) of water. If a gauge is not
available, check by removing the exhaust pipes from
the exhaust manifold. With the exhaust pipes
removed, start the engine and load the engine on a
dynamometer to see if the problem is corrected.
4.
Low quality fuel:
Test
the
engine
with
fuel
according
to
recommendations by Caterpillar Inc.
5.
Fuel setting incorrect:
Check and make necessary adjustments as per
Testing and Adjusting Section of the Service
Manual. See Fuel Setting And Related Information
Fiche for the correct fuel setting.
6.
Incorrect fuel injection timing dimension:
Check and make necessary adjustments as per
Testing and Adjusting Section of the Service
Manual.
7.
Valve adjustment is not correct or valve leakage:
Check and make necessary adjustments as per
Testing and Adjusting Section of the Service Manual.
Intake valve lash is 0.38 mm (.015 in) and exhaust
valve lash is 0.64 mm (.025 in).
8.
Defective fuel injectors:
Defective fuel injectors will normally cause the
engine to "misfire" (injection not regular) and run
rough, but can cause too much smoke with the
engine running smooth. Remove and check the
fuel injectors. Use the 1U6661 Pop (Injector)
Tester to check the injectors for proper operation.
Refer
to
Special
Instruction,
SEHS8867
for
additional information.
9.
Governor problem:
Bench test the governor. If the governor cannot be
properly adjusted during bench testing, repair or
replace the governor. Perform a bench test on
repaired or replacement governor. Verify that the
settings are correct for air fuel ratio control.
Engine Runs Rough
Probable Cause(s):
10.
Misfiring cylinders:
Refer to Problem No. 4, Engine Misfiring Or
Running Rough.
11.
Fuel injection timing not correct:
Check and make necessary adjustments as per
Testing and Adjusting Section of the Service
Manual.
12.
Air in fuel system:
With air in the fuel system the engine will normally be
difficult to start, run rough and release a large amount of
white smoke. If air is in the system, it will generally get
in on the suction side of the fuel transfer pump. Check
for leakage at the connections between the fuel tank
and the fuel transfer pump. If leaks are found, tighten
the connections or replace the lines. If there are no
visual leaks, remove the fuel supply line from the tank
and connect it to an outside fuel supply. If this corrects
the problem, the suction line (standpipe) inside the fuel
tank has a leak.
If this does not correct the problem, install a sight tube
in the fuel return line and check the injectors to verify
that they are properly seated. This can be
accomplished by moving each injector (one at a time)
to the "FUEL ON" position momentarily and checking
the sight tube for any increase in air bubbles. Push on
the rack bar on the exhaust manifold side of the
injector to move the injector to the "FUEL ON" position.
If an increase in air is found, then remove that injector.
Check the tip seal (O-ring) and replace if it is defective.
Inspect the injector sleeve for a smooth sealing surface
for the injector to seat on. If any defects are noted, the
sleeve can be reamed or it can be replaced if
necessary.
6-44
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