and high idle. If the pressure is excessive, a restricted fuel return line is the probable cause.

To test for restricted fuel supply on the suction side of the pump, operate the engine at high idle and read the vacuum developed. If the vacuum reading exceeds 10 inches mercury (Hg), check the fuel supply system for dirty filters, pinched or collapsed hoses, or a plugged vent.

Removal

If, after field testing, you find you must remove the injection fuel pump from the engine, be sure to remove all external grease and dirt. Remember, dirt, dust, and other foreign matter are the greatest enemies of the injection fuel pump. As a precaution, keep all openings plugged during removal and disassembly.

Disassembly

The workbench, surrounding area, and tools must be clean. You should have a clean pan available to put parts into as you disassemble the pump, You also need a pan of clean diesel fuel oil in which the parts can be washed and cleaned.

After mounting the pump in a holding fixture, clamp the fixture in a vise. Now you are ready to disassemble the pump. Follow the step-by-step procedure in the manual for the model pump on which you are working. Figure 5-18 shows the main internal working parts of the Roosa Master fuel injection pump.

Cleaning, Inspecting, and Reassembly

Now that you have disassembled the pump, and inspected all the parts carefully, replace all O rings, seals, and gaskets, and inspect all springs for wear, or distortion. Clean and carefully check all bores, grooves, and seal seats for damage of any kind. Replace damaged parts as necessary.

Also, inspect each part of the injection pump for excessive wear, rust, nicks, chipping, scratches, cracks, or distortion. Replace any defective parts.

When you have finished cleaning and inspecting the pump, reassemble it. Follow the steps specified by the manufacture's maintenance and repair manual.

Figure 5-18.-Roosa Master fuel injection pump.

AMERICAN BOSCH FUEL INJECTION PUMP

The American Bosh fuel injection pump is used on multifuel engines. This pump meters and distributes fuel. It is a constant-stroke, distributing-plunger, sleeve-control type of pump. As with other fuel systems, only clean fuel should be used. Good maintenance of the filtering system and reasonable care in fuel handling will give trouble-free operation. Fuels used in the multifuel engine must contain sufficient lubrication to lubricate the fuel pump and injectors. Because of close tolerances, extreme cleanliness and strict adherence to service instructions are required when it is time to service this pump.

In this section, you will learn about the operation and troubleshooting of the American Bosch, Model PSB, pump and the Bosch nozzles that are used with the International Harvester engines.

Operation

The purpose of the fuel pump (fig. 5-19) is to delivcr measured quantities of fuel, accurately, under high pressure to the spray nozzle for injection. The positive