A drop or two of fuel at the spray tip is only an indication of the fuel trapped in the spray tip at the beginning of the test. It is not detrimental as long as the pressure drop specified is not less than 40 seconds.
HIGH-PRESSURE TEST. - This testis performed to discover arty fuel leaks at the injector filter cap gaskets, body plugs, and nut seal ring which did not appear during the valve holding pressure test. The high-pressure test also indicates whether the injector plunger and bushing clearance are satisfactory. To perform the test, place the injector rack in the FULL-FUEL position. Operate the pump handle (fig. 5-30) to build up and maintain a pressure of 1,600 to 2,000 psi. Then inspect the injector filter cap gaskets, body plugs, and injector nut seal ring for leaks.
Next, you should use the adjusting screw in the injector tester handle to depress the injector plunger just far enough to close both ports in the injector bushing. Both ports are closed if the injector spray decreases and the pressure rises. Now, you can determine the condition of the plunger and bushing. If there is excessive clearance between the plunger and bushing, it means that pressure will not rise beyond the normal valve-opening pressure. Next, you should replace the
SPRAY PATTERN TEST. - This test is performed after you have completed the valve holding pressure test. After placing the injector in the tester, open the fuel shutoff valve; then place the injector rack in the FULL-FUEL position. Operate the injector several times in succession by pumping the tester handle (fig. 5-31) at approximately 40 strokes per minute. Observe the spray pattern to see whether all of the spray tip orifices are open and injecting evenly. The beginning and ending of injection should be sharp, and the fuel injected should be finely atomized. If all the spray tip orifices are not open and injecting evenly, clean the orifices in the spray tip during injector overhaul.
To prevent damage to the pressure gauge, do not exceed 250 psi during this test.
You should visually inspect the injector plunger even if the injector passes all of the previous tests. The plunger is visually checked under a magnifying glass for excessive wear or a possible chip on the bottom helix. There is a small area on the bottom helix and the lower portion of the upper helix, that, if chipped, will not be indicated in any of the tests.
FUEL OUTPUT TEST. - This test is performed to check injector fuel output. To test the injector, place it plunger and bushing.
Figure 5-30.-Injector high-pressure test.
Figure 5-31.-Spray pattern test.Continue Reading