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
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.
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
manufactures maintenance and repair manual.
Figure 5-18.-Roosa Master fuel injection pump.
AMERICAN BOSCH FUEL INJECTION
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
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.
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