NOZZLE OPERATION. The pressurized
fuel from the injection pump enters the top of the
nozzle body and flows through a passage in the
body and nozzle spring retainer. An annular
groove in the top face of the nozzle valve body tills
with fuel, and two passages in the nozzle valve
body direct fuel around the nozzle valve. When the
fuel in the pressure chamber reaches a
predetermined pressure, the spring force (adjusted
by shims) is overcome and injection occurs.
Atomized fuel sprays from the orifice holes in the
nozzle tip as the nozzle valve is opened inward by
pressurized fuel. When injection ends, spring
pressure snaps the valve in its seat. During each
injection, a small quantity of high pressured fuel
passes between the nozzle valve stem and the
nozzle valve body to lubricate and to cool the
nozzle valve. A manifold that connects to all of the
nozzles returns this fuel to the tank.
NOZZLE TROUBLESHOOTING. You can
check the condition of a nozzle before it is
disassembled by using the field test (Kiene).
Remove the nozzle from the engine, and using the
test pump shown in figure 5-27, check for nozzle
spray angle and pattern. There are four orifices in
the nozzle tip, and the spray angle should be
uniform from all four. Also, check the spray valve
opining pressure. A pressure reading that is more
than 50 psi below the specified opening pressure of
Figure 5-27.-Test pump.
the valve indicates a need to adjust the pressure
by adding shims. Next, test the leakage past the
seat and stem. If this leakage is excessive due to
wear, install a new nozzle valve.
Proceed with nozzle disassembly only after you
have performed these and other tests prescribed in
the test manual. While testing, record the results
of the tests for each nozzle. They can help you
determine the nature and extent of necessary
Before you disassemble the nozzle, clean the
external area with cleaning fluid or clean diesel
fuel oil, using a brush with long, soft bristles.
Keep the disassembled nozzles separated to
prevent mixing the various components. During
inspection, refer to the test results which are used
as a guide to determine the extent of
After you have disassembled the nozzle, make
sure each disassembled nozzle has been placed in
a separate pan containing a cleaning solvent or
clean diesel fuel oil. Soak the tips in a good carbon
removal compound for the length of time
prescribed by the manufacturer.
As a word of caution, remember NOT to mix
the tips together. Each tip must be reassembled
with its own group parts.
Be careful when you clean the spray holes of
the nozzle tip so that you do not enlarge or
damage them. Use a magnifying glass during your
inspection for signs of scratches, corrosion, or
erosion on the spring retainer, the nozzle body
holder, and the valve body face. Also, check the
stem and the body of the valve, making sure they
do not bind.
Reassemble the nozzle in the manner
prescribed and specified by the manufacturers
maintenance and repair manual.
Before you install the nozzle in the engine,
retest it for spray angle and pattern, valve
opening pressure, and leakage past the seat and
stem. When test results are good, install the
nozzle in the engine.
GENERAL MOTORS FUEL INJECTION
The General Motors fuel injection system
includes fuel injectors, fuel pipes, fuel manifolds,
fuel pump, fuel strainer, fuel filter, and fuel lines
connecting the fuel tank. The operation of this
system depends on the