DECREASED PWR. (TEAR IN ATAAC) AIR TO AIR AFTER COOLER HOSE

SUBJECT: DECREASED POWER/TEAR IN THE AIR TO AIR AFTER COOLER (ATAAC) HOSE

MODELS: 1990-91 C6H and C7H TOPKICK/KODIAK EQUIPPED WITH 3116 CATERPILLAR DIESEL ENGINES (RPO LXO & VIN Code J)

THIS BULLETIN CANCELS AND REPLACES GMC TRUCK SERVICE BULLETIN 91-6A-97, DATED MAY 1991 TO INCLUDE THE NECESSARY ILLUSTRATIONS. ALL COPIES OF 91-6A-97 SHOULD BE DISCARDED.

The turbocharger outlet hose to the Air To Air After Cooler may tear. In most cases, the tear is only a surface tear through the rubber portion of the hose. The material portion (inner sheath) of the hose is the part of the hose that retains the boost pressure. If the inner portion of the hose is torn, a high pitched whine will be audible and is usually accompanied with a loss of power.

The molding process of the ATAAC hose required a specific thickness of rubber. The additional thickness of rubber can give rise to tearing.

A new ATAAC hose (Figure 2), made with a different process, is now available for service. The new ATAAC hose is made with a hump in the center and can be used, without modification, on the models listed above.

VEHICLES INVOLVED

The new ATAAC hose was installed in production on all vehicles built after the following VIN break- points.

GMC Truck: 1GDM7HlJ8MJ512250 Chevrolet: 1GBJ7HlJ9MJ106991

SERVICE PROCEDURE (FIGURE 1):

1. Loosen upper and lower constant torque clamps (1).

2. Remove existing hose (3).

3. Install new hose (Part Number 15679504) between the turbocharger and the turbo-boost tube (1).

4. Position the hose and turbo boost tube in a manner that allows clearance between the turbo-boost tube and the turbocharger outlet flange.

5. Torque the upper and lower constant torque clamps to 5.5 - 6.0 N-m (4-4.5 lbs. ft).

SERVICE PARTS INFORMATION:

Part Number Description Quantity -------- ---------------------- -------- 15679504 Intercooler Hump Hose 1

Parts are currently available from GMSPO.

WARRANTY INFORMATION

For vehicles repaired under warranty use: Labor Operation: J9745

NOTE: Labor Operation is coded to base vehicle coverage in the warranty system.

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.