DECREASED POWER/TORN HOSE TURBOCHARGER NEW ATAAC HOSE

SUBJECT: DECREASED POWER/TORN TURBOCHARGER TO AIR TO AIR AFTERCOOLER HOSE (NEW ATAAC HOSE)

VEHICLES AFFECTED: 90-91 6H, 7H W/CAT 3116 ENGINE (RPO LXO VIN J)

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 moulding 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, as shown in Figure 2, made with a different process, is now available for service. The new ATAAC hose is made with a hump in the centre 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 breakpoints.

GMC Truck: 1GDM7H1J8MJ512250

SERVICE PROCEDURE Refer to 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 ft. lbs. ) .

SERVICE PARTS INFORMATION:

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

Parts are currently available from CANSPO.

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.