INCREASED ENGINE NOISE (NEW A.I.R. ADAPTER)

MODELS: 1988 C/K/R AND EARLY BUILT 1989 C/K/R TRUCKS W/7.4L (VIN CODE N) ENGINE

Some 1988 C, K, R and early built 1989 C, K, and R trucks with 7.4L engine and serpentine drive may receive customer comments of increased engine noise. When investigating this condition, a check of the Air Injection Reaction (A.I.R.) injection valve adapter tube should be made. A broken or cracked adapter tube could account for a noise condition. A new adapter with a support tab, P/N 10129509 is now available and may be used with a rework of the A/C compressor A.I.R. pump mounting bracket.

Parts are currently available from GMSPO.

Service Procedure: (See Illustration)

1. Remove old adapter

2. Temporarily install new adapter to determine hole location for support tab.

3. On trucks with air conditioning, remove compressor from mounting bracket and lay aside. DO NOT DISCHARGE REFRIGERANT FROM SYSTEM.

4. On trucks without air conditioning, remove idler pulley bracket and save for reinstallation.

5. Scribe location of the support tab on A/C compressor/A.I.R. pump bracket.

6. Drill 5/16" hole in bracket.

7. Install new adapter, and attach support tab to bracket using 11509589 bolt, 9439511 washer, and 11508279 nut. Torque to 20-27 Nm. (14- 20 lbs/ft).

8. Reinstall A/C compressor and/or idler pulley bracket.

For vehicles under warranty, use:

Labor Operation Number: T7840 Labor Time: .6 Hr

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.