For 1990-2009 cars

# EXHAUST BOOM (NOISE) REPAIR PROCEDURE

#### MODELS AFFECTED: 1985-1986 DE VILLES AND FLEETWOODS

Some De Villes and Fleetwoods equipped with an HT4100 engine may experience an exhaust boom (noise) between 1830 - 1890 R.P.M.

To correct this condition, a new exhaust hanger bracket kit (P/N 25527855) has been developed. Vehicles which experience this condition should be serviced using the following procedure:

1. Verify the exhaust boom is present with A/C off.

2. If boom is not present with A/C off, see Serviceman Bulletin 84-102A, Group 1, number 17 and 85-100, Group 1, number 24 for A/C system diagnosis.

3. Clamp the new hanger to the tailpipe as shown in Figure 1. The weld-nut on the hanger assembly should line up with the centerline of the muffler.

4. Position the leading edge of the new body mounted exhaust hanger bracket against the old exhaust hanger bracket keeping the bottom edge flush with the bottom of the frame rail. Drill three 5/16 diameter holes in frame using bracket as a guide and secure with the three self-tapping screws included in the kit.

5. Support the exhaust system and remove the original insulator and attaching bolts. Cut the point from the top bolt to shorten it to 10 mm (13/32 in.) of thread length.

6. Re-install the insulator at the new location.

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.