for a fault in other parts of the engine; damage to the
engine will result.
When you check the fuel pump on the engine,
remove the pipe plug from the pump shutoff valve and
connect the pressure gauge. At the governed speed (just
before the governor cuts in), maximum manifold
pressure should be obtained. If the manifold pressure is
NOT within specified limits, adjust for maximum
manifold pressure by adding or removing shims from
under the nylon fuel adjusting plunger in the bypass
valve plunger. Be careful you do not lose the small lock
washer that fits between the fuel adjusting plunger and
the plunger cap.
To check the suction side of the pump, connect the
suction gauge to the inlet side of the gear pump. The
valve in the pump, if properly adjusted, should read 8
inches on the gauge. When the inlet restrictions reaches
8.5 to 9 inches, change the fuel filter element and remove
any other sources of restriction. The engine will lose
power when the restriction is greater than 10 to 11
Always make the above checks on a warm engine.
Also, operate the engine for a minimum of 5 minutes
between checks to clear the system of air.
If the pump manifold and suction pressures are
within specified limits and there is still a loss of power,
you should check the injectors.
Carbon in the PT injector metering orifices restricts
the fuel flow to the injector cups, which results in engine
power loss. Remove the carbon from the metering
orifices by reverse flushing; it should be performed on
a warm engine. To remove carbon, perform the
1. Loosen all injector adjusting screws one turn
from the bottom or one and one-eighth turns from the
set position. Lock with the jam nut after completing the
2. Start the engine and accelerate with maximum
throttle from idling to high-10 to 15 times.
3. Readjust the injectors to their standard setting.
The engine will be difficult to start with the loose
injector setting; it will smoke badly and will be sluggish.
If the injector adjusting screws are loosened, the meter
orifice will not be closed during injection. Extremely
high injection pressure will force some of the fuel to
backflow through the orifice and should remove carbon
deposits. If this method is not effective, remove the
injectors for cleaning.
When working on the PT fuel system of a
turbocharged Cummins engine, you may find an aneroid
control device. This device creates a lag in the fuel
system so that its response is equivalent to that of the
turbocharger, thus controlling the engine exhaust
emissions (smoke level).
The aneroid is an emissions control device.
Removing it or tampering with it is in direct
violation of state and federal vehicle exhaust
During troubleshooting of the fuel system, you
should check the aneroid according to the
If you determine that the fuel pump (fig. 5-34) must
be removed from the engine, take the following
. Make sure the shop area is clean.
l Use clean tools.
Good cleaning practices are essential to good
quality fuel pump repair. Take special care when the PT
fuel pump, which is made of a lightweight aluminum
alloy, is disassembled. Use proper tools to prevent
damage to machined aluminum surfaces, which are
more easily damaged than parts made of cast iron.
Before disassembling the unit, try to determine what
parts need replacement.
After you place the fuel pump on the holding device,
place the device in a vise and disassemble the pump.
Follow the procedures given in the manufacturers
maintenance and repair manuals.
Pump Cleaning and Inspection
Now that the pump has been disassembled, you
should clean and inspect all parts. Do not discard parts
until they are worn beyond reasonable replacement
limits. The PT fuel pump parts will continue to function
long after they show some wear. Parts that are worn
beyond reasonable replacement limits must not be
reused. From experience you know reasonable
replacement limits. Reuse all those parts that will give
another complete period of service without danger of