EXHAUST RATTLE/RINGING NOISE 3.4L V6 ENGINE (INFORMATIONAL)

SUBJECT: EXHAUST RATTLE/RINGING NOISE (REPLACE MUFFLER ASSEMBLIES AND EXHAUST INTERMEDIATE PIPE)

VEHICLES AFFECTED: 1991-92 "W" MODELS WITH 3.4L ENGINE (VIN X, RPO LQ1)

CONDITION:

--------- Some 1991-92 W-cars with 3.4L V-6 engines (RPO LQ1), may exhibit an audible metallic rattle/ringing type noise that appears to be coming from the rear underbody area of the vehicle, evident during vehicle warm-up after cold start.

CAUSE:

----- Combination of the engine fuel/air ratio prior to reaching normal operating temperature and unequal length exhaust takedown pipes, generate exhaust pulses that create a resonance in the exhaust system.

CORRECTION:

---------- Replace existing exhaust intermediate pipe, right and left hand muffler assemblies with new components indicated below by vehicle configuration.

NOTICE: Owners should be informed prior to servicing vehicle, that the amplitude of the sporty/throaty exhaust note of the system will be appreciably reduced with installation of these new components. Knowing this, some owners may wish to forego the servicing of their vehicle for correction of the rattle/ringing noise apparent only during vehicle warm up.

CHEVROLET

Vehicle Configuration Part Description P/N --------------------- ---------------- --- Coupe Intermediate Pipe 12520500 L.H. Muffler Asm. 10220039 R.H. Muffler Asm. 12520499 Clamp 10114745

Sedan Intermediate Pipe 12520500 L.H. Muffler Asm. 10220040 R.H. Muffler Asm. 12520501 Clamp 10114745

PONTIAC

Vehicle Configuration Part Description P/N --------------------- ---------------- --- With Aero Performance Intermediate Pipe 12520500 Package (RPO B4U) L.H. Muffler Asm. 10220048 R.H. Muffler Asm. 12520506 Clamp 10114745

W/Out Aero Performance Intermediate Pipe 12520500 Package (RPO B4U) L.H. Muffler Asm. 10220041 R.H. Muffler Asm. 12520503 Clamp 10114745

OLDSMOBILE

Vehicle Configuration Part Description P/N --------------------- ---------------- --- All Intermediate Pipe 12520500 L.H. Muffler Asm. 10220042 R.H. Muffler Asm. 12520505 Clamp 10114745

To insure proper installation follow the procedure in the applicable Service Manual Section 6F, Exhaust System.

NOTICE: Insure that damper assemblies mounted on muffler crossover pipe are reinstalled if vehicle was equipped with such. Not installing damper may result in an exhaust moan/boom in the 2300-2500 rpm range.

WARRANTY INFORMATION:

For vehicles repaired under warranty use:

Labour Time: 0.8 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.