Metering (fig. 5-30) - The plunger is just beginning to move downward and the engine is on the beginning of the compression stroke. The fuel is trapped in the cup, the check ball stops the fuel flowing backwards, and fuel begins to be pressurized. The excess fuel flows around the lower annular ring, up the barrel, and is trapped there.

Pre-injection (fig. 5-30) - The plunger is almost all the way down, the engine is almost at the end of the compression stroke, and the fuel is being pressurized by the plunger.

Injection (fig. 5-30) - The plunger is almost all the way down, the fuel injected out the eight orifices, and the engine is on the end of the compression stroke.

Purging (fig. 5-30) - The plunger is all the way down, injection is complete, and the fuel is flowing into the injector, around the lower annular groove, up a drilled passageway in the barrel, around the upper annular groove, and out through the fuel drain. The cylinder is on the power stroke. During the exhaust stroke, the plunger moves up and waits to begin the cycle all over.

Injector adjustments are extremely important on PT injectors because they perform the dual functions of metering and injecting. Check the manufacturer's manual for proper settings of injectors. On an engine where new or rebuilt injectors have been installed, initial adjustments can be made with the engine cold. Always readjust the injectors, using a torque wrench calibrated in inch-pounds after the engine has been warmed up. Engine oil temperature should read between 140F and 160F.

Anytime an injector is serviced, you must be certain that the correct orifices, plungers, and cups are used, as these can affect injection operation. You can also affect injection operation by any of the following actions:

Improper timing.

Mixing plungers and barrels during teardown (keep them together, since they are matched sets).

Incorrect injector adjustments after installation or during tune-up adjustment.

Installing an exchange set of injectors without taking time to check and correct other possible problems relating to injection operation. This is often overlooked.

Proper injector adjustment and maintenance will ensure a smooth running engine as long as the following factors are met:

1. Adequate fuel delivery pressure from the fuel pump to the fuel manifold.

2. Selection of the proper sizes of balance and metering orifices.

3. The length of time that the metering orifice is uncovered by the upward moving injector plunger.

NOTE For required adjustments and maintenance schedules, always consult the manufacturer's service manual.

Celect System

The Celect system is a full electronic controlled injection and governing system. The major reason behind the adoption of electronic fuel injection control is to be able to meet not only the EPA (Environmental Protection Agency) exhaust emission controls but also ensure optimum fuel economy. This is done by constantly monitoring major engine operating parameters that have a direct bearing on engine combustion efficiency. A number of engine- and vehicle-mounted sensors are used to update timing and metering values continually. The Celect system controls the following major operating factors:

1. Engine torque and horsepower curves

2. AFC (air-fuel control) to limit exhaust smoke

3. Engine low idle and high speeds

4. Functions as a vehicle road speed governor

5. Optional vehicle/engine cruise control

6. PTO (power takeoff) operation

7. Idle shutdown, 3 to 60 seconds

8. Gear down protection

For the Celect system to operate, major components are required. These components are as follows: