OPERATION OF FUEL INJECTION PUMPS

FUEL SYSTEM

SYSTEMS OPERATION

(75V1-UP, 90N6121-UP)

Constant bleed valve (4) lets approximately 9

Injection will stop (see position 3) when fuel

gallons of fuel per hour go back to fuel tank (7).

outlet (E) is lifted above the top edge of sleeve (D)

This fuel goes back to fuel tank (7) through return

by camshaft (4). This movement lets the fuel that

line for constant bleed valve (3). This flow of fuel

is above, and in, plunger (B) go through fuel outlet

removes air from housing (14) and also helps to

(E) and return to the fuel injection pump housing.

cool the fuel injection pump. Check valve (D)

makes a restriction in this flow of fuel until the

When the sleeve (D) is raised on plunger (B), fuel

pressure in housing (14) is at 8 3 psi (0.6 0.2

outlet (E) is covered for a longer time, causing

more fuel to be injected in the engine cylinders. If

kg/cm2 ).

sleeve (D) is low on plunger (B), fuel outlet (E) is

covered for a shorter time, causing less fuel to be

OPERATION OF FUEL INJECTION PUMPS

injected.

The main components of a fuel injection pump

OPERATION OF 9L6969 FUEL INJECTION NOZZLE

in the sleeve metering fuel system are barrel (A),

plunger (B), and sleeve (D), Plunger (B) moves up

The fuel inlet (6) and nozzle tip (13) are parts of

and down inside the barrel (A) and sleeve (D).

the nozzle body (11). Valve (8) is held in position

Barrel (A) is stationary while sleeve (D) is moved

by spring force. Force of the spring is controlled

up and down on plunger (B) to make a change in

by pressure adjustment screw (3). Locknut (4)

the amount of fuel for injection.

holds pressure adjustment screw (3) in position.

The lift of valve (8) is controlled by lift adjustment

When the engine is running, fuel under pressure

screw (2), Locknut (10) holds lift adjustment

from the fuel transfer pump goes in the center of

screw (2) in position, Compression seal (7) goes on

plunger (B) through fuel inlet (C) during the down

nozzle body (11).

stroke of plunger (B), Fuel can not go through fuel

outlet (E) at this time because it is stopped by

The compression seal goes against inlet fitting

sleeve (D), (see position 1),

(6) and prevents the leakage of compression from

the cylinder. Carbon dam (12), at the lower end of

Fuel injection starts (see position 2) when

nozzle body (11), prevents the deposit of carbon in

plunger (B) is lifted up in barrel (A) enough to

the bore in the cylinder head.

close fuel inlet (C). There is an increase in fuel

pressure above plunger (B), when the plunger is

lifted by camshaft (4). The fuel above plunger (B)

is injected in to the engine cylinder.

FUEL INJECTION NOZZLE

1. Cap. 2. Lift adjustment screw. 3. Pressure adjustment

screw. 4. Locknut for pressure adjustment screw. 5. O-ring seal.

6. Fuel Inlet. 7. Compression seal. 8. Valve. 9. Orifice (four).

10. Locknut for lift adjustment screw. 11.

Nozzle body. 12. Carbon dam. 13. Nozzle tip.

Fuel, under high pressure from the fuel injection

pump goes through the hole in fuel inlet (6). The

fuel then goes around valve (8), fills the inside of

nozzle body (11) and pushes against the valve

guide. When the force made by the pressure of the

FUEL INJECTION SEQUENCE

fuel is more than the force of the spring, valve (8)

will lift. When valve (8) lifts, fuel under high pres-

1, 2, 3. Injection stroke (position) of a fuel Injection

sure will go through the four .0128 in. (0.325 mm)

pump. 4. Injection pump camshaft. A, Barrel. 0. Plung-

orifices (9) into the cylinder. When the fuel is sent

er. C. Fuel Inlet. D, Sleeve. E. Fuel outlet. F, Lifter.