DIESEL INJECTION NOZZLE REVISED NOZZLE TEST PROCEDURE

MODELS: ALL GMC C, K, OR G 1500-3500 MODELS EOUIPPED WITH 6.2L V8 DIESEL ENGINES

The following revised injection nozzle test procedures for subject engine should be used instead of those shown in Section 6C6 of the Light Duty Truck Shop Manual.

INJECTION NOZZLE

Nozzles used in C-K models or G models are different and are not interchangeable.

Removal

1. Disconnect batteries. (2)

2. Disconnect fuel line clip.

3. Remove fuel retum hose.

4. Remove fuel injection line as previously outlined.

5. Remove injection nozzle using tool J-29873 whenever possible.

NOTE: When removing an injection nozzle, use tool J-29873. Be sure to remove the nozzle using the 30 mm. hex. Failure to do so will result in damage to the injection nozzle. Always cap the nozzle and lines to prevent damage and contamination.

Testing

Test is comprised of the following checks:

Nozzle Opening Pressure

Chatter

Leakage

Spray Pattern

Each test should be considered a unique test (i.e., when checking opening pressure, do not check for leakage).

If all of the tests are satisfied, the nozzle holder assembly can be again installed in the engine without any changes. If any one of the tests is not satisfied, the complete nozzle holder assembly must be replaced. The nozzle holder will then be further checked and repaired at a centralized location.

Test Lines - 6 x 2 x 400 mm. (1.5 mm. bore).

Test Fluid per ISO 4113 (Example Shell V1399, Viscor 1487c or equivalent).

Kinetic Viscosity at 40 DEG) per ISO 3104: 2.45-2.75 mm. 2/second.

Test Oil Temperature during Test: 20-25 DEG C (room temperature).

Refer to the equipment manufacturer's instructions for exact test procedures.

CAUTION:

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 poisioning. The nozzle tip should always be enclosed in a receptacle, preferably transparent, to contain the spray.

Test Sequence

Preparation:

1. Connect the nozzle holder assembly to the test line.

2. Place clear plastic tubes on overflow connections to prevent leakoff from being confused with actual leak.

3. Close the shutoff valve to the pressure gage.

4. Fill and flush the nozzle holder assembly with test oil by activating the lever repeatedly and briskly. This will apply test oil to all functionally important areas of the nozzle and purge it of air.

Obtaining Pressure Check:

1. Open shutoff valve at pressure gage 1/4 turn.

2. Depress lever of tester slowly. Note at what pressure the needle of the pressure gage stopped. Some nozzles may pop, others may drip down at this time (this is not leakage). The maximum observed pressure is the opening pressure.

3. The opening pressure should not fall below the lower limit of 105 bar or 10,400 kpa (1500 psi on used nozzles).

4. Replace nozzles which fall below the lower limit.

Leakage Test:

1. Further open shutoff valve at pressure gage (1/2 to 1-1/2 turns).

2. Blow-dry nozzle tip.

3. Depress lever of manual test stand slowly until gage reads a pressure of 95 bar or 9,500 kpa (1400 psi). Observe tip of nozzle. A drop may form but not drop off within a period of 10 seconds.

4. Replace the nozzle holder assembly if a droplet drops off the nozzle bottom within the 10 seconds.

Chatter Test:

When testing for chatter, it should be noted that the sound (chatter) for new and used nozzles may vary.

On used nozzles, carbonized fuel oil deposited on the pintle and on the nozzle tip produces different sound (chatter) between new and used nozzles on the test stand.

With some used nozzles, the chatter is difficult to detect during slow actuation of the hand test stand lever. Some nozzles may chatter more (louder) than others. As long as there is chatter, the nozzle is acceptable.

1. Close shutoff lever at pressare gage.

2. Depress lever of manual test stand slowly, noting whether chatter noises can be heard.

3. If no chatter is heard, increase the speed of lever movement until it reaches a point where the nozzle chatters. At fast lever movement, the nozzle may emit a "hissing" or "squealing" sound rather than the normal "chatter"; this is acceptable.

4. These sounds indicate that the nozzle needle moves freely and that the nozzle seat, guide, as well as the pintle, have no mechanical defects.

5. Replace nozzles which do not chatter.

Spray Pattern:

This nozzle features a longer nozzle overlap, greater pintle to body clearance, and greater needle to body clearance. This assembly also features an internal wave washer between the nozzle nut and nozzle. Because of these features, objective testing is difficult. A pop tester will not deliver fuel with the velocity necessary to obtain proper spray pattern analysis. Based on the above, this type nozzle should not be rejected for spray pattern.

General Motors bulletins are intended for use by professional technicians, not a "do-it-yourselfer". They are written to inform those technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions and know-how to do a job properly and safely. If a condition is described, do not assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See a General Motors dealer servicing your brand of General Motors vehicle for information on whether your vehicle may benefit from the information.