carbon on the inside of the tip. Then they can be cleaned
out by using the proper size spray tip cleaning wire.
Inspect injector parts for excessive wear, damage,
defects, burrs, scratches, scoring, erosion, or chipping.
Replace the damaged or excessively worn parts.
Lap all of the sealing surfaces, such as the bottom
of the injector body, the injector bushing, the valve seat,
the valve cage, the check valve, and the spray tip, before
you reinstall used valve parts in an injector.
Now you are ready to reassemble the injectors.
Follow the steps prescribed by the manufacturer’s
maintenance and repair manuals. The injector is
satisfactory if it passes these tests. Failure to pass any
one of the tests indicates that defective or dirty parts
have been assembled. In this case, disassemble, clean,
inspect, reassemble, and test the injector again.
CUMMINS PRESSURE TIME FUEL
INJECTION SYSTEM
The Cummins Pressure Time (PT) Fuel Injection
System (fig. 5-33) consists of the fuel pump (with
governor), the supply lines, drain lines, fuel filters, fuel
injectors, and shutdown valve. An aneroid valve is
installed on the fuel system of turbocharged engines
only.
As in previous sections of this chapter, we will cover
troubleshooting, disassembly, inspection, reassembly,
and testing of components. Remember, before
performing any service on the PT injector or pump, refer
to the manufacturer’s maintenance and repair manuals.
Troubleshooting
Troubleshooting is an organized study of a problem
and a planned method or procedure to investigate and
correct the difficulty.
Most troubles are simple and easy to correct; for
example, excessive fuel oil consumption is caused by
leaking gaskets or connections. A complaint of a sticking
injector plunger is usually corrected by repairing or
replacing the faulty injector; however, something
caused the plunger to stick. The cause maybe improper
injector adjustment, or, more often, water in the fuel.
In general, the complaint of low pwer is hard to
correct because it can have many causes. There are many
variables in environmental operation and installations,
and it is difficult to measure power in the field correctly.
With the PT fuel system, you can often eliminate the
pump as a source of trouble. Simply check to see that
the manifold pressure is within specified limits. The fuel
rate of the pump must not be increased to compensate
Figure 5-33.-Pressure-timed injection system.
5-26
