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 (9) Test under high pressure. This test is made to
completely disassembled, inspected, reassembled and tested.
uncover any leaks at injector filter caps, body plugs, or seal
(5) Test for plunger freeness. Depress injector
rings which did not appear during holding pressure test.
follower and release. A slow return of the follower will denote
Position the injector rack at full fuel and depress injector
a sticky injector plunger. Inability to fully depress the follower
plunger with popping handle just far enough to close both
usually indicates a scored plunger and bushing. Perform this
ports in the bushing. At the same time operate the pump
test with the injector rack in three different positions; full fuel,
handle to build and maintain a pressure of 1,400 to 2,000 psi.
no fuel, and a point midway between these two positions. If a
The point at which ports are closed may be ascertained by the
binding plunger is noted, the injector must be completely
fact that the injector spray will change appreciable and a rise
disassembled, cleaned, inspected, reassembled, and tested.
in pressure will occur. The popping handle may be held in
(6) Test for spray pattern. With injector rack in
proper position for this test by means of the handle lock (3)
full fuel position, operate pump handle (4) to maintain a fuel
and adjusting screw (2). While maintaining a pressure of
pressure of approximately 15 psi. Pop the injector several
1,400 to 2,000 psi inspect for leaks at the injector filter caps,
times by depressing the popping handle, and observe the
body plugs and seal ring.
spray pattern emerging from each orifice. The spray pattern
should be uniform.
g. Installation.
(7) Test for correct valve opening pressure. Place
(1) Insert the injector into the injector tube with
injector rack in full fuel position. Operate pump handle with
the locating dowel registering with the locating hole in the
smooth even strokes and at the same time, observe the
cylinder head, and with the pin on injector control arm lever
pressure gage noting at what pressure the injector sprays fuel.
registering with injector control rack lever.
The valve opening pressure should be from 450 to 850 psi on
(2) Place injector clamp over stud and replace
a new injector and from 350 to 850 psi on a used injector. If
washer and nut. Tighten nut to 25 foot-pounds.
valve opens at a pressure lower than the above minimums, it
(3) Position rocker arm assembly and replace
indicates damaged or dirty sealing surfaces or a fatigued or
rocker arm bolts. Torque bolts to 100 foot-pounds.
worn valve spring. If any of these conditions exist, the injector
(4) Connect fuel lines to injector and fuel
nut must be removed and the valve parts cleaned, inspected,
connections.
repaired, reassembled, and tested.
h. Timing Fuel Injectors. After installation, the injectors
(8) Test injector holding pressure. Operate pump
must always be timed before the engine is run to insure
handle to bring pressure to a point just below the injector
proper fuel delivery to each cylinder at the correct moment.
valve opening pressure. Close the shutoff valve and note the
To insure proper injection timing, the plunger follower of each
pressure on the gage. Check the pressure drop by timing.
injector must be adjusted to a certain position in relation to the
On a new injector the pressure should drop from 450 to 250
injector body. If the injectors are not properly timed, the
psi in not less than 50 seconds. On a used injector the
engine operation will be "ragged" and power output reduced.
pressure should drop from 450 to 250 psi in not less than 50
(1) Stop engine and leave throttle in the STOP
seconds. On a used injector the pressure should drop from
position.
350 to 150 psi in not less than 35 seconds. If the injector fails
(2) Bar over engine by hand, or by means of the
to hold these pressures, leaks in lines leading to injectors and
cranking motor until the exhaust valves of the cylinder to be
on the injector itself are indicated. A leak in the injector rack
timed are fully opened.
opening indicates excessive clearance between plunger and
(3) Place the stem of the correct injector timing
bushing or between bushing and injector body. A leak around
gage (3, fig. 5-44) in the correct timing gage hole in top of
the spray tip or seal ring is usually caused by a loose injector
injector body (4).
nut, a damaged seal ring, or a scored surface on nut or spray
tip. A "dribble" or drop at spray tip indicates a leaking valve
assembly.
5-54
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