3304 & 3306 – Fuel Injection Pump Operation

1. Reverse flow check valve. 2. Chamber. 3. Barrel. 4. Spring. 5. Fuel inlet (fill port). 6. Retainer. 7. Plunger. 8. Sleeve. 9. Fuel outlet (spill port). 10. Sleeve control lever. 11. Lifter. 12. Camshaft.

The main components of a fuel injection pump in the sleeve metering fuel system are: plunger (7), barrel (3), and sleeve (8). The plunger moves up and down inside the barrel and sleeve. The barrel is stationary while the sleeve is moved up and down around the plunger to make a change in the amount of fuel for injection.

The plunger, barrel, and sleeve are a fitted set and they must be kept together. Lifter (11) and plunger (7) are lifted through a full stroke by each revolution of the camshaft (12). The force of spring (4) on plunger (7) through retainer (6) holds the lifter against the camshaft through the full stroke cycle.

2. Chamber. 3. Barrel. 5. Fuel inlet (fill port). 7. Plunger. 8. Sleeve. 9. Fuel outlet (spill port). 11. Lifter. 12. Camshaft. A. Before injection. B. Start of injection. C. End of injection.

Before Injection

Before the engine can start or run correctly, the housing and fuel injection lines must be full of fuel and the sleeve (8) must be high enough on the plunger to close the fuel outlet (9) (spill port) during part of the stroke cycle. Chamber (2) fills with fuel through the fuel inlet (5) (fill port) which is under the level of the fuel in the housing.


Injection starts after the rotation of the camshaft lifts plunger (7) far enough into barrel (3) to close fuel inlet (5). At this time, both the fuel inlet and fuel outlet are closed. As more rotation of the camshaft lifts the plunger farther into the chamber of the barrel, the fuel in the chamber is put under more and more pressure. This pressure is felt by reverse flow check valve (1) and the fuel injection valve. When the pressure is high enough to open the fuel injection valve, injection starts. Injection stops when the rotation of the camshaft has lifted the plunger far enough to open fuel outlet (9). This puts the fuel outlet above the top of sleeve (8).

When the fuel outlet opens, it lets pressure off of the fuel in the chamber. The pressure of the fuel in the line closes the reverse flow check valve (1). With no more flow of fuel, injection valve at the other end of the line closes. This makes the injection complete. The volume of fuel in the injection charge is equal to the volume of the plunger which is lifted into the barrel between the start of injection and the end of injection.

After Injection

After injection has stopped, the camshaft lifts the plunger the rest of the way to the top of the stroke. The plunger is pushed out of the chamber by spring (4). The fuel in the housing fills the space in the chamber through the fuel outlet (9) until the sleeve closes it on the down stroke. More rotation of the camshaft lets the spring push the plunger down farther which opens fuel inlet (5). Fuel fills the rest of the chamber through the fuel inlet (5). Then the stroke cycle starts again.

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