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

Model and Year: 1988-90 C1, C3, K3, R2 TRUCKS WITH 7.4L (VIN CODE N) ENGINE

THIS BULLETIN CANCELS AND SUPERSEDES DEALER SERVICE BULLETIN NO. 89-66-6E, DATED JANUARY 1989. THE C1 TRUCK HAS BEEN ADDED AS WELL AS THE 1990 MODEL YEAR. ALSO, CHANGES IN THE SERVICE PROCEDURE HAVE BEEN MADE. DISCARD ALL COPIES OF 89-66-6E.

Condition:

Some 1988-90 C/K and R trucks with 7.4L engine and serpentine drive may receive customer comments of increased engine noise.

Cause:

Tube assembly between the Air Injection Reaction (A.I.R.) Management Valve and A.I.R. pump may be cracked or broken.

Correction:

A new design consisting of a bracket assembly, molded hose and adapter has been released. See the following Service Procedure:

SERVICE PROCEDURE: (SEE ILLUSTRATION)

1. Remove old adapter.

2A. On trucks that DO NOT have the support tab on the adapter tube, temporarily install new design hose, bracket and hose adapter to determine hole location for bracket.

2B. Trucks that DO HAVE the support tab on the adapter tube will have one hole and weld nut already located on A/C Compressor/A.I.R. Pump Bracket.

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

3B. On trucks without air conditioning, remove idler pulley bracket and save for reinstallation.

4. Scribe location of new bracket assembly on A/C compressor/A.I.R. pump bracket.

5. Drill 5/16" hole/s in A/C bracket using new bracket assembly as template.

6. Install New Parts:

10045710 Adapter Asm. - One Required

10129577 Bracket Asm. - One Required

10129578 Hose - One Required

11508106 Bolt - One or Two Required - See Step 2A and 2B

11507036 Nut - One or Two Required - See Step 2A and 2B

Parts are currently available from GMSPO.

7. Torque all bolts to 20-27 N.m. (14-20 lbs. ft.).

8. Reinstall A/C Compressor or Idler Pulley.

Labor Operation Number: T1620

Labor Time: On C/K/R With Air Conditioning .6 Hour On C/K/R Without Air Conditioning .5 Hour

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.