Fuel lnjector
2.1.1
DETROIT DIESEL 53
not fall freely. loosen the injector nut. turn the tip.
injector tester to equal or exceed the capacity of
then retighten the nut. Loosen and retighten the nut a
the pressure gage.
couple of times if neccessary. Generally this will free
the rack. Then. if the rack isn't free. change the
injector nut. In some cases it may be necessary to
INJECTOR VALVE HOLDING PRESSURE
disassemble the injector to eliminate the cause of the
TEST
misaligned parts.
The injector valve holding pressure test will determine
whether the various lapped surfaces in the injector are
INJECTOR HIGH PRESSURE TEST
sealing properly.
Operate the pump handle to bring the pressure up to
This test is preformed to discover any leaks at the
approximately 450 psi.
injector filter cap gaskets. body plugs and nut seal
ring.
Close the fuel shut-off valve and note the pressure
The high pressure test also indicates whether or not
drop. The time for a pressure drop from 450 psi to 250
psi must not be less than 40 seconds. If the pressure
the plunger and bushing clearance is satisfactory.
drop is less than 40 seconds. Check the injector as
1. Install the Injector in tester J 9787.
follows.
1. Thoroughly dry the Injector with compressed air.
CAUTION: When testing an injector Just
r e m o v e d from an engine, the flow of fuel
2. Open the tester fuel valve and operate the pump
through the injector on the tester should be the
handle to maintain the test pressure.
same as in the engine. Connections on the test
head of the tester may be changed to obtain the
3. A Ieak around the spray tip or seal ring usually is
correct direction of flow.
caused by a loose injector nut. a damaged seal ring or
a brinelled surface on the injector nut or spray tip.
2. Thoroughly dry the injector with compressed air.
4. A leak at the filter cap indicates a loose filter cap or
3. Check the fuel connections for leaks. If leaks have
a damaged filter cap gasket.
occurred. tighten the connections. dry the injector and
recheck.
5 . A "dribble" at the spray tip orifices indicates a
leaking valve assembly due to a damaged surface or
4. With the injector rack in the full-fuel position and
dirt. Leakage at the tip will cause pre-ignition in the
the injector tester handle locked in position by means
engine.
of the handle lock (Fig. 9), operate the pump handle
to build up and maintain the pressure.
NOTE: A drop or two of fuel at the spray tip is
only an indication of the fuel trapped in the
At this time. the condition of the plunger and bushing
spray tip at the beginning of the test and is not
may be established. If there is excessive clearance
detrimental as long as the pressure drop
between the plunger and bushing, pressure beyond the
specified is not less than 40 seconds.
normal valve opening pressure cannot be obtained.
Replacement, of the plunger and bushing assembly is
then required.
SPRAY PATTERN TEST
Pump up the injector tester and maintain a pressure of
1600 to 2000 psi by actuating the pump handle. Then
After completing the valve holding pressure test, open
inspect for leaks at the injector filter cap gaskets, body
the fuel shut-off valve, place the injector rack in the
plugs and injector nut seal ring. If any of these
full-fuel position and operate the injector several times
conditions exist, refer to Trouble Shooting Chart 5 in
in s u c c e s s i o n by operating the tester handle at
Section 2.0.
approximately 40 strokes per minute as shown in
Fig. 10. Observe the spray pattern to see that all spray
NOTE: It is normal for fuel to seep out around
orifices are open and injecting evenly. The beginning
the rack due to high pressure fuel being applied
and ending of injection should be sharp and the fuel
to a normally low pressure area in the injector
injected should be finely atomized.
assembly. However, fuel droplets at the rack
indicate excessive leakage.
If all of the spray tip orifices are not open and
injecting evenly. clean them during injector overhaul.
CAUTION: Do not permit the pressure in the
Also refer to Trouble Shooting Chart 6 in Section 2.0.
March. 1973
SEC. 2.1.1 Page 7
