Unless special servicing equipment and repair
instructions are available, defective nozzles and pumps
are usually exchanged for new ones. However, in an
emergency, and if spray valves or pumps are not too
badly worn, they may be returned to a serviceable con-
dition, with minor adjustment, after a thorough cleaning.
Injector spray nozzles or pumps should never be
disassembled in the field. They should be removed
from the equipment and brought to the shop for repair.
Figure 4-50.--Cleaning injector spray nozzle holes.
The first requirement for the cleaning job is a clean
NOTE: Because of the physical location of the unit
Use clean diesel fuel for washing the parts.
injectors under the valve covers, and because the
Disassemble one nozzle or pump assembly at a time to
dripping fuel from a loosened injector line would drain
prevent mixing of mating parts. Exercise care to
down into the crankcase, the above test cannot be
prevent damage to nozzle and pump parts. Inspect and
performed on a GM diesel. To test a GM diesel injector,
clean all parts as they are disassembled. Carbon may be
the valve cover must be removed and each unit injector
scraped from the outside of the nozzle, but be careful
follower depressed one at a time with a screwdriver or
not to mar the edges of the holes (orifices). When
similar device. This will isolate each injector to
cleaning fluid is used to clean pump and nozzle parts,
determine if it is faulty.
dip the parts in diesel fuel immediately after cleaning.
If an injector appears to be faulty, you can check its
This will prevent moisture from the hands from marring
performance with a nozzle tester. This instrument may
the highly polished surfaces.
be used without taking the injector apart. Nozzle testers
Reaming tools and special drills are provided for
all work on the same principle. The injector is
cleaning spray nozzle holes. No drills other than those
connected to a hand pump with which you force fuel
recommended by the manufacturer should be used. The
through the injector. A pressure gauge is attached to the
drills are hand operated, and the smaller, needle-type
pump so that you can note the opening (cracking)
drill should be held with a small chuck called a pin vise
pressure at which the injector is set. You can easily test
for leakage and see the spray pattern as the fuel comes
In performing reaming operations, remove only the
out of the injector. Ensure eye protection is worn and all
foreign matter; be particularly careful not to burr the
body parts are protected from the high-pressure spray.
1. Rocker injector arm
5. Injector follower
2. Push rod
4. Fuel injector
6. Injector timing gauge
Figure 4-51.--Timing fuel injectors with injector timing gauge.