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