Fuel Injector Testing.

TM 10-3930-634-34

NOTE

tion and the injector tester popping handle locked in

Immediately after removal of the fuel pipes

position by means of the handle lock, operate the

from the injectors, cover the filter caps with

pump handle to build up and maintain the pressure at

1600 to 2000 psi by actuating the pump handle. Then

shipping caps to prevent dirt from entering

the injector. Also cover the fuel pipes and

inspect for leaks at the injector f ilter cap gaskets, body

connectors to prevent entry ofdirt or foreign

plugs and injector nut seal ring.

material.

NOTE

(3) Crank the engine with the starting motor to

If there is excessive clearance between the

plunger and bushing, pressure beyond the

bring the push rod ends, outer ends of the injector and

normal valve opening pressure cannot be ob

the valve rocker arms in line horizontally.

(4) Remove the rocker arm shaft bracket bolts and

tained. Replacement of the plunger and bush-

fuel injector clamp as illustrated in figure 3-31. Pivot

ing assembly is then required.

rocker arms back as shown.

(5) Remove the injector as illustrated in figure

It is normal for fuel to seep out around the

3-32.

c. Fuel Injector Testing.

rack due to high pressure fuel being applied

(1) General. If inspection does not reveal any ex-

to a normally low pressure area in the injec-

tor assembly. However, fuel droplets at the

ternal damage, make a series of tests to determine the

rack indicate excessive leakage.

condition of the injector to avoid unnecessary repair.

(e) Relieve test pressure slowly to prevent dam-

An injector that passes all the tests outlined below is

age to test gage.

considered satisfactory for service. Test the fuel injec-

(4) Injector Holding Pressure Test.

tor as follows:

(a) Operate pump handle to bring pressure up to

(2) Control Rack and Plunger Movement.

(a) Place the fuel injector in a tester, with the

approximately 450 psi (fig. 3-34).

(b) Close fuel shut-off valve and note pressure

dowel in the underside of the injector located in the

proper slot or hole in the adapter plate. Position the

drop. The time for a pressure drop from 450 psi to 250

psi should be not less than 40 seconds.

handle support to proper height (fig. 3-33).

(c) If injector pressure drops from 450 psi to

CAUTION

When testing an injector just removed from

250 psi in less than 40 seconds, inspect injector for

an engine, the flow of fuel through the injec-

leaks as follows:

1. Thoroughly dry injector with compressed

tor on the tester should be the same as in the

engine. Connections on the test head of the

air.

2. Open tester fuel valve and operate the

tester may be changed to obtain the correct

direction of flow.

pump handle to maintain testing pressure (fig. 3-34).

(b) Place handle on top of injector follower then

3. Check for a leak at injector rack opening. A

leak indicates a poor bushing-to-body fit.

close inlet and outlet clamps to hold injector in tester.

4. A leak around the spray tip or seal ring usu-

With injector control rack held in the NO FUEL posi-

ally is caused by a loose injector nut, a damaged seal

tion, push handle down and depress follower to bottom

ring, or a brinelled surface on injector nut or spray tip.

of its stroke. Slowly release pressure on handle while

5. A leak at filter cap indicates a loose filter

moving control rack back and forth, as shown in figure

3-33 until the follower reaches top of its travel. If the

cap or a damaged filter cap gasket.

6. A "dribble" at spray tip orifices indicates a

rack does not move freely it indicates that internal

leaking valve assembly due to a damaged surface or

parts of the injector are misalined, damaged or dirty.

(3) High Pressure Test.

dirt.

(5) Spray Pattern Test.

(a) Install injector in test stand as shown in

figure 3-34.

CAUTION

(b) Thoroughly dry the injector with com-

To prevent damage to pressure gage, do not

pressed air.

exceed 250 psi.

(a) After completing injector holding pressure

have occurred, tighten the connections, dry the injec-

test, open fuel shut-off valve, then place injector rack

tor and recheck.

in full-fuel position and operate injector several times

CAUTION

in succession by operating tester popping handle at ap-

Do not permit the pressure in the injector

proximately 40 strokes per minute as shown in figure

tester to equal or exceed the capacity of the

3-34. Observe the spray pattern to see that all spray

pressure gage.

orifices are open and injecting evenly. The beginning

(d) With the injector rack in the full-fuel posi-

3-27