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.