GMC 4000 Series Service Manual page 372

NOTE: Once fuel is noticed at the secondary
filter, it may take one or two minutes more before
clear fluid will flow, depending upon the condition
of all filters.
4. Loosen fuel inlet line fitting at left side of
pump hydraulic head (11, fig. 9). Pump hand prim­
er and purge all air from line from secondary
filter to hydraulic head. Tighten line nut.
5. Disconnect the fuel return line at fuel in­
jection pump overflow valve. Remove leak-off lines,
then loosen overflow valve.
6. Again pump the hand primer until a solid
stream of fuel flows from the overflow valve at the
injection pump. Once clear fuel starts to flow,
tighten overflow valve and the system is primed.
7. Connect fuel return lines to overflow valve.
NOTE: It will be necessary to crank the engine
until fuel is supplied to the nozzles before engine
will start.
IMPORTANT: Do not crank engine for more
than ten (10) seconds at a time. Wait for intervals
of ten (10) to fifteen (15) seconds when prolonged
cranking is required. E xcessive cranking may
cause damage to starter windings. In addition, oil
pressure will be high enough at the fuel injection
pump excess fuel device to cause it to reduce fuel
delivery for starting. Waiting 10 to 15 seconds will
allow oil pressure to drop off and again allow ex­
cess fuel device to return to excess fuel position.
8. After engine starts, set hand throttle for
1,000 engine rpm, then loosen bleeder plug at se c ­
ondary filter (3, fig. 9) and allow any air in fuel
lines to purge. Tighten bleeder plug.
9. With engine still operating at 1,000 rpm,
loosen fuel line nut at each fuel injector nozzle
allowing any air in hydraulic head and each high
pressure line to purge. As each line is purged, it
is normal for engine speed to drop approximately
300 rpm. (Refer to "Fuel Injection N ozzles" later
in this section for locating a misfiring cylinder.)
Torque each fuel line nut to 20 to 25 foot-pounds.
METHOD B - USING PRESSURIZED
SUPPLY TANK
A pressurized fuel supply tank can be used to
prime the fuel system in place of the hand primer
pump mentioned previously. A pressure tank can
be improvised locally by using a brake system air
tank or sim ilar container equipped with a threaded
type filler cap, an air pressure gauge, a fuel outlet
fitting and a shut-off valve.
With the pressurized supply tank outlet valve
closed, fill the tank X full of clean fuel. Install the
filler cap securely and apply 35 to 45 pounds air
pressure to the tank. Follow the same procedure
for priming the system as shown previously under
''Method A - Using Mechanical Pump." The p res­
surized tank should be connected into the system
in place of the hand pump.
G M C S E R V I C E M A N U A L
FUEL INJECTION SYSTEM— TORO-FLOW ENGINE
priming method and the pressurized tank priming
method, is that with the former method fuel is
pumped from the vehicle fuel tank through the sy s­
tem and not supplied from an external source.
IZED TANK TO BE DEPLETED AS UNWANTED
AIR WILL ENTER SYSTEM.
METHOD C - USING AN ORDINARY
FUEL CONTAINER
priming equipment, as mentioned in the previous
priming methods, is not available:
pour spout, or one with a drain tube which incor­
porates a shut-off. A large hand operated oil-can
may also be used.
which will allow the secondary filter, with lines
attached, to be raised and supported at an eleva­
tion slightly above the fuel injection pump. Support
the filter assembly so that it remains in the raised
position.
at the fuel injection pump and loosen the valve.
1 Fuel Injection Pump
7 Filter Drain Plug
A ssem bly 8 C lips
2 Pump Discharge Line 9 Fuel Suction Line
3 Bleeder Plug
4 Secondary Filter 10 Fuel Pump Assembly
5 Filter Clamp Bolt 11 Fuel Supply Line (To
6 Filter Mounting
Bracket
Figure 9 — Fuel Secondary Filter and Connecting Lines
NOTE: The difference between the hand pump
DO NOT ALLOW FUEL SUPPLY IN PRESSUR­
CAUTION
When priming the diesel engine, DO
NOT prime the system with pressure ex­
ceeding 35 to 45 psi; it could cause a rup­
ture of the element in secondary filter.
NOTE: This method should be used only when
1. Procure a clean container having a small
2. Remove necessary clips, bolts and nuts
3. Disconnect lines leading to overflow valve
Sec. 6M
Page 361
(To Pump)
Injection Pump)