Fuel Injector: Testing and Inspection

WARNING: When testing nozzles, do not place your hands or arms near the tip of the nozzle. The high pressure atomized fuel spray from a nozzle has sufficient penetrating power to puncture flesh and destroy tissue and may result in blood poisoning. The nozzle tip should always be enclosed in a receptacle, preferably transparent, to contain the spray.

If an injection nozzle is not properly delivering fuel into the pre-combustion chamber of a cylinder, driveability could be greatly effected, or a diagnostic trouble code could be set. If other diagnosis indicates, or if the injection nozzles are suspected of not properly delivering fuel, they should be tested.

Nozzle testing is comprised of the following checks:

- Nozzle opening pressure.
- Leakage.
- Chatter.

NOTE: Each test should be considered independent of the others (for example, when checking opening pressure, do not check for leakage). If all of the following tests are satisfied, the nozzle assembly can be reused. If any one of the tests is not satisfied, the complete nozzle assembly must be replaced. When performing the injection nozzle tests, refer to the instructions provided with the nozzle tester J 29075-B.

PREPARATION FOR INJECTION NOZZLE TEST
- Position a nozzle tester on a workbench.
- Install one nozzle on the tester fitting.
- Place a container under the nozzle that will deflect the nozzle spray absorb the test fluid.
- Install two clear plastic hoses (11/2 in. long) over the leak-off fittings.
- Close the shutoff valve at the pressure gauge.
- Operate the lever of the nozzle tester repeatedly and briskly to fill and flush the nozzle with test oil.

NOZZLE OPENING PRESSURE TEST
1. Open the shutoff valve at the pressure gage one-quarter turn.
2. Depress the tester lever slowly. Note at what pressure the needle of the pressure gage stopped. The maximum observed pressure is the opening pressure.

- Some nozzles may pop while other nozzles may drip down (this is not leakage).

3. The opening pressure should not fall below the lower limit of 105 bar (1500 psi) for naturally aspirated engines and 117 bar (1700 psi) for turbo-charged engines for used nozzles.
4. Replace nozzles which fall below the lower limit.

NOZZLE LEAKAGE TEST
1. Further open the shutoff valve at the pressure gage (1/2 to 11/2 turns).
2. Blow dry the nozzle tip.
3. Depress the lever of the manual test stand slowly until the gage reads a pressure of 95 bar (1400 psi). Observe the nozzle tip. A drop may form on the end of the nozzle but should not drop off within a period of 10 seconds.
4. Replace the nozzle assembly if a drop falls during the 10 seconds.

CHATTER TEST

NOTE: When testing for chatter, it should be noted that the sound (chatter) for new and used nozzles may vary. This is due to carbonized fuel deposits on the pintle and nozzle tip of used nozzles. With some used nozzles, chatter is difficult to detect during slow actuation of the hand lever. Some nozzles may chatter louder than others. As long as there is chatter, the nozzle is acceptable.

1. Close the shutoff lever at the pressure gage.
2. Depress the lever of the test stand slowly and note whether chatter noise can be heard.
3. If no chatter is heard, move the lever faster until it chatters. At fast lever movement, the nozzle may make a "hissing" or "squealing" sound rather than then normal chatter. This is acceptable.
4. These sounds indicate that the nozzle needle moves freely and that the nozzle seat, guide, and pintle are OK.
5. Replace nozzles that do not chatter.