GMC 4000 Series Service Manual page 381

Sec. 6M
Page 370
FUEL INJECTION SYSTEM— TORO-FLOW ENGINE
Figure 2 4 — Installing Fuel Injection Nozzle Assem bly
NOTE: When new pressure adjusting spring is
installed, adjust the opening pressure 10% higher
than specification to allow for spring set.
4. After correct valve opening pressure is
obtained, tighten cap nut (4, fig. 19) firmly to lock
the adjustment. Recheck for valve opening p res­
sure after cap nut is tightened.
5. Operate test pump handle with several fast
sharp strokes, meanwhile observing spray pattern.
Spray should be in the nature of finely atomized
sprays indicating that all holes are open. Nozzle
tips have only four orifices.
6. Stroke pump slowly (approx. 3 seconds).
Some degree of "chatter" should occur, indicating
that nozzle valve is free and component parts are
correctly assembled.
Figure 2 5 — Tightening Nozzle H older
Bolts with Torque W rench
G M C S E R V I C E M A N U A L
Torque Both B olts Progressively
in Steps Indicated Below:
Step 1 Tighten to 4 Foot-Pounds
Step 2 Tighten to 8 Foot-Pounds
Step 3 Tighten to 12 Foot-Pounds
Step 4 Tighten to 17 Foot-Pounds
7. Depress the pump handle slowly with a 10-
second stroke and hold the pressure slightly (ap­
prox. 100 lbs.) below nozzle valve openingpressure
to check for valve seat leakage. No fuel droplets
should appear. Occasionally a slight wetting of the
tip (2, fig. 22) may be noticed. This is perm issible
since it is caused from hydraulically balancing the
spring and nozzle valve.
8. Remove the nozzle holder assembly (3, fig.
22) from test stand (11, fig. 22) and close the high
pressure threaded connection with plastic cap to
prevent entrance of dirt. If nozzle holder is not to
be installed immediately, it should be wrapped in
clean paper.
NOTE: If nozzle does not function properly
when tested, a new valve and body should be install­
ed in holder; or a new or rebuilt nozzle holder a s­
sembly should be installed when assembling engine.
NOZZLE HOLDER ASSEMBLY INSTALLATION
Before a nozzle holder assembly is installed
in cylinder head, the cavity or well in cylinder
head must be clean. A nozzle seat cleaner (J-21762)
and hole brush (J-8152) should be used to remove
all deposits from nozzle holder well. Use seat
cleaner and wrench handle (fig. 23) first to clean
seat, and the bore in cylinder head through which
the injection nozzle valve body extends, then use
brush to finish cleaning the well cavity.
1. Use new copper gasket at lower end of in­
jection nozzle assembly and insert the nozzle hold­
er assembly into place in cylinder head (fig. 24).
2. Install two bolts with lock washers (one
long bolt and one short bolt is used at each nozzle)
into tapped holes in cylinder head assembly. Use
torque wrench (fig. 25) and gradually tighten nozzle
holder bolts alternately to avoid any tendency to
bend the holder assembly.
NOTE: Final tension on two nozzle holder
bolts should be equal to seat assembly squarely on
copper gasket. This can best be accomplished by
torquing bolts in four steps. Torque each bolt first
to four foot-pounds, then to eight foot-pounds,
twelve foot-pounds and then seventeen foot-pounds
(fig. 25).
3. Install leak-off lines (fig. 6) between in­
jection nozzles and at fuel overflow valve on in­
jection pump. To facilitate installation, the ends
of leak-off lines may be warmed in hot water. Ends
of plastic tubing should be pushed onto fittings so
that ends seat at shoulder.
4. Install fuel lines as explained later under
''High Pressure Fuel Line Installation."
HIGH PRESSURE FUEL LINE
INSTALLATION
NOTE: Whenever it is necessary to replace
high pressure fuel lines, it is important to use only