Chevrolet 70 1969 Series, Shop Manual

Page: 345 / 913

ENGINE FUEL SYSTEM 6M -18
FUEL INJECTION AND GOVERNOR SYSTEM
(6V-53 ENGINES)
FUEL SYSTEM— GENERAL
The fuel system consists of the fuel primary
filter, fuel pump, fuel secondary filter, fuel lines
and injectors as shown in figure 1.
A .070” restricted fitting is located in the cyl­
inder head fuel return manifold outlet to maintain
pressure within the fuel system, between the fuel
pump and restricted fitting.
On some models a check valve, if required, is
installed in the supply line between the fuel tank
and fuel primary filter, to keep the fuel oil from
draining back into the fuel tank when the engine is
shut down.
The fuel pump draws fuel from the tank through
the primary filter, and forces it under pressure
through the secondary filter. From the secondary
filter, the fuel is forced through the fuel inlet pass­
age in the cylinder head and fuel lines to the in­
jector.
The fuel passes through a filter elementwithin
the injector to a chamber where it is metered,
displaced, and atomized through the spray tip into
the combustion chamber.
Heat generated by the high compression of air
ignites the fine fuel spray and combustion contin­
ues until the fuel is burned.
Fuel in excess of that required for engine
operation is circulated through the injectors by the
fuel pump. In addition to serving as a coolant,
circulation of the surplus fuel bleeds any air or
vapor in the system back to the fuel tank where it
is vented to the atmosphere. Surplus fuel leaving
the injectors flows through the outlet fuel line to
the fuel return passage, through a restricted fit­
ting, and back to the fuel supply tank.
FUEL INJECTORS
D ESCRIPTION
The G M unit fuel injector illustrated in figure
2, is a lightweight compact unit which enables
quick easy starting directly on Diesel fuel and per­
mits the use of a simple open type combustion
chamber. The simplicity of design and operation
provides for simplified controls and easy adjust­
ment. No high pressure fuel lines or complicated
air-fuel mixing or vaporizing devices are required.
The unit fuel injector performs five functions:
1. Creates the high fuel pressure required for
efficient injection.
2. Meters and injects the fuel to the exact
amount required to handle the load.
3. Atomizes the fuel for mixing with the air in
the combustion chamber.
4. Distributes the fuel throughout the air in
the combustion chamber.
5. Permits continuous fuel flow.
Combustion required for satisfactory engine
operation is obtained by injecting, under pressure,
a small quantity of accurately metered and finely
atomized fuel oil into the combustion chamber.
Metering of the fuel is accomplished by an
upper and lower helix machined in the lower end of
the injector plunger. Figure 3 illustrates the fuel
metering from NO-LOAD to F ULL- LOAD by rota­
tion of the plunger in the bushing.
Figure 4 illustrates the phases of injector
operation by the vertical travel of the injector
plunger.
The continuous fuel flow through the injector
serves, in addition to preventing air pockets in the
fuel system, as a coolant for those injector parts
subjected to high combustion temperatures.
To vary the power output of the engine, injec­
tors having different fuel output capacities are
used. The fuel output of the various injectors is
governed by the helix angle of the plunger and the
type of spray tip used. Refer to figure 5 for the
identification of the injectors and their respective
plungers and spray tips.
CHEVROLET SERIES 70-80 H EAVY DUTY TRUCK SH O P M A N U A L