Service Operations - GMC 4000 Series Service Manual

Sec. 6M
Page 360
FUEL INJECTION SYSTEM— TORO-FLOW ENGINE
bubbles rising to surface of oil. Bubbles indicate
points where fuel leaks will occur during normal
operation of supply pump.
d. If supply pump leaks are discovered, the
defective seal, gasket, or other component must be
replaced, or the supply pump overhauled or replac­
ed by a serviceable unit. Supply pump overhaul
procedure is given under appropriate headings
Do not attempt to work on the fuel injection pump, nozzles, or high pressure
lines in a dusty area. Extreme precautions must be taken to prevent any dust par­
ticles from entering the fuel passages in lines and nozzles. Any dirt or abrasive
material permitted to enter the fuel supply port on fuel injection pump could quickly
cause extensive damage to, or possibly ruin the pump hydraulic head mechanism.
Figure 8 is a cut-away view of the injection pump hydraulic head which will aid in
understanding the fuel system.
DELIVERY
VALVE SPRING
VALVE RETAINER
HEAD
DELIVERY
VALVE
SCREW
Figure 8 — H ydraulic H ead S h o w in g
Internal Com ponents
G M C S E R V I C E M A N U A L

SERVICE OPERATIONS

W A RN IN G
SOCKET
HEAD SCREW
RETAINER
FUEL
CONTROL
UNIT
SPACER
LOCKWIRE
CONTROL UNIT
A N D ROD
RETAINER PLATE
CONTROL ROD vf
previously in this section.
3. If no evidence of fuel leakage has been
found in procedure described under Steps 1 and 2
previously, refer to "Replacing Hydraulic Head"
covered later in this section. Follow applicable
instructions to remove the hydraulic head a ssem ­
bly from fuel injection pump housing and replace
head lower O-ring seal in housing (fig. 37).
PRIMING DIESEL FUEL SYSTEM
In the event fuel supply is exhausted from fuel
tank, and in cases when the fuel filters, fuel injec­
tion pump and/or nozzles, or fuel lines, have been
replaced it may be necessary to prime the system
by use of one of the methods explained following:
ALL AIR MUST BE PURGED FROM SYSTEM
BEFORE ENGINE WILL RUN PROPERLY.
METHOD A - USING MECHANICAL PUMP
A small hand operated pump which is available
through the Parts Department can be installed in
the fuel supply line between the fuel tank and prim ­
ary filter as a temporary or permanent installation.
It is suggested that a pump used as a temporary
installation be equipped with flexible inlet and out­
let hoses having the necessary fittings to connect
into the system . Complete installation instructions
are furnished with the priming pump. After in­
stalling the pump, prime the system as follows:
1. Remove plug from top of primary filter,
then operate hand pump to purge all air from the
primary filter back to fuel tank. Reinstall plug.
2. Remove the small hex bleed plug at the top
of the secondary fuel filter (3, fig. 9) located on
the engine.
3. Pump the hand primer until a clear stream
of fluid flows from air bleed plug hole on the s e c ­
ondary filter. The bleed plug can be installed as
soon as all air bubbles disappear.