GMC 4000 Series Service Manual page 367

Sec. 6M
Page 356
FUEL INJECTION SYSTEM— TORO-FLOW ENGINE
1 Camshaft Gear
2 Injection Pump D rive
Gear
3 D rive Gear Bolts
4 Self Locking Bolt
5 Camshaft Gear
Retainer
6 Lock Plates
7 Balance Shaft Idler
Gear
Figure 5 — Gear Train and Timing Marks
Refer to figure 1 for schematic arrangement
of injection pump internal mechanism.
FUEL INJECTION NOZZLES
Fuel under pressure is fed from the rotary
single plunger injection pump to the appropriate
nozzle via the high pressure pipe line and finds its
way through the ducts in the nozzle holder and
valve body to the lower end of valve.
When the fuel pressure reaches 3,000 psi, the
valve will lift, and fuel is injected through holes
in nozzle tip and into combustion chamber. Nozzle
valve closes again when the line pressure drops.
Any leak-back through the leak-off line fitting is
passed back to the junction fitting on injection
pump overflow valve.
G M C S E R V I C E M A N U A L
8 Balance Shaft Thrust
Plate
9 Balance Shaft Gear
10 Gear Retainer Plate
11 Plate Retaining Bolts
12 Crankshaft Balancer
Key
13 Cylinder Block
14 Camshaft Idler Gear
FUEL INJECTION NOZZLE
HOLDER ASSEMBLIES
The fuel injection nozzle and holder assem ­
blies are utilized to carry the high pressure fuel
(red color in fig. 1) through the cylinder head to
nozzle tip and deliver it to the combustion cham­
ber in the form of a finely atomized spray through
the precision-drilled spray holes in the tip.
The nozzle holder consists of a forged body
which houses the spindle and spring, and has a high
pressure fuel duct. The spindle bore and spring
chamber are utilized as a passage for leak-off fuel
which seeps past and lubricates the nozzle valve.
The nozzle valve and body are a closely match­
ed pair of parts which must always be used to­
gether as a unit. VALVES AND VALVE BODIES
ARE NOT INTERCHANGEABLE; however, matched
nozzle and valve assem blies are available for
service replacement. Refer to "Nozzle and Holder
Assembly Maintenance" covered later in this s e c ­
tion under "Fuel Injection N ozzles." Nozzle and
valve assembly is located on nozzle holder by
dowel pins and the assembly is firmly seated at
lapped mating surfaces on body and nozzle holder
by the nozzle cap nut. A high pressure duct in noz­
zle valve body registers with the corresponding
duct in nozzle holder to carry high pressure fuel
to the valve seat area. Pressure spring at upper
part of holder seats at a flange on spindle, and
spring is retained by the pressure adjusting nut.
Spring pressure is transferred through the spindle
to the nozzle valve. Spring holds the valve on its
seat in nozzle body.
A perfect seal is necessary at valve seat to
prevent fuel dribble as well as to prevent any of
the combustion gases in cylinder from entering the
spray nozzle interior chamber.
The cap nut at upper end of nozzle holder a s­
sembly serves to lock the spring adjusting nut and
is threaded to accept a leak-off tee or elbow to
which is attached the leak-off hose.
A high pressure fuel line from outlet port in
injection pump hydraulic head is connected to
threaded portion on nozzle body forging.
The fuel injection nozzle holder assem blies
are held in place in cylinder heads by two bolts;
and a copper gasket is used at bottom of each noz­
zle well in head.
FUEL LINES
FUEL SUPPLY AND RETURN LINES
Rigid supply lines carry fuel from fuel tank
and primary filter along vehicle frame to a point
near the rear end of engine. A sim ilar return line
carries fuel from engine to fuel tank. Flexible
hoses are employed to connect supply line to inlet
fitting at fuel supply pump, and to connect the out­
let fitting on overflow valve (at injection pump) to