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Figure 3-22. Fuel injector in testing and popping fixture, installation.
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TM-10-3930-243-34 Truck Lift Fork Diesel Engine Pneumatic Tired Wheels Rough Terrain 10 000 lb. Capacity 24 Inch Load Center Manual
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Figure 3-23. Fuel injector high pressure test.
will decrease appreciably and a rise in pressure will
2. Open the tester fuel valve and operate
occur.
the pump handle to maintain test pressure.
(c) At this time the condition of the plunger
3. Check for leak at the injector rack
and bushing may be established. If there is ex-
opening. A leak indicates a poor bushing-to-body
cessive clearance between the plunger and bushing,
fit.
pressure beyond the normal valve opening pressure
4. A leak around the spray tip or seal ring
cannot be obtained. Replacement of the plunger
usually is caused by a loose injector nut, a damaged
and bushing assembly is then required.
seal ring, or a brinelled surface on the injector nut
or spray tip.
(d) P u m p u p t h e i n j e c t o r t e s t e r a n d
maintain a pressure of 1600 to 2000 psi by ac-
5. A leak at the filter cap indicates a
tuating the pump handle. Inspect for leaks at the
loose filter cap or a damaged filter cap gasket.
injector filter cap gaskets, body plugs, injector nut
6. A "dribble" at the spray tip orifices
seal ring area.
i n d i c a t e s a leaking valve assembly due to a
damaged surface or dirt. Leakage at the tip will
NOTE
cause preignition in the engine.
It is normal for some fuel leakage at the rack hole due
to high pressure fuel being applied to a normally low
NOTE
pressure area in the injector assembly.
A drop or two of fuel at the spray tip is only an in-
dication of fuel trapped in the spray tip at the
CAUTION
beginning of the test and is not detrimental as long as
Do not permit pressure in the injector
the pressure drop specified is not less than 40
tester to equal or exceed the capacity of
seconds.
the pressure gage.
(3) Spray pattern test.
(5) Visual inspection of plunger. An injector
(a) With injector mounted in the tester and
which passes all the previous tests should have the
the injector rack in Full Fuel position, operate the
plunger checked visually, under a magnifying glass,
pump handle to maintain a fuel pressure just below
for excessive wear or a possible chip on the bottom
the valve opening pressure.
helix. There is a small area on the bottom helix and
(b) Operate the injector several times with
lower portion of the upper helix, if chipped, that
the pump handle and observe the spray pattern
will not be indicated in any of the test. Remove the
emitted from the spray tip orifices. Fuel should be
plunger from the injector as follows:
discharged from each orifice and spray should
(a) S u p p o r t  i n j e c t o r , right side up, in
produce a uniform pattern.
holding fixture.
(c) If spray does not produce a uniform
(b) Compress the follower spring. Using a
pattern, clean orifices in the spray tip (fig. 3-29).
screwdriver, raise the spring above the stop pin
(4) High pressure test.
and withdraw the pin (fig. 3-24). Allow the spring
(a) With the injector rack in the Full Fuel
to rise gradually.
position and the injector tester handle locked in
(c) Remove the injector from the holding
p o s i t i o n by means of handle lock (fig. 3-23),
fixture. Turn injector upside down, to prevent the
operate pump handle to build up and maintain the
entry of dirt, and catch spring and plunger as they
pressure.
fall out.
(b) Use the adjusting screw in the injector
(d) Inspect the plunger, and if chipped at
tester handle to depress the injector plunger just far
lower helix (fig. 3-21), replace the plunger and
enough to close both ports in the injector housing.
bushing assembly.
The point at which both ports are closed may be
easily ascertained by the fact that the injector spray
3-36

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