CHASSIS SYSTEMS NOISES/DIAG. CONDITIONS & CORRECTIONS

Subject: CHASSIS SYSTEMS RELATED UNDERBODY NOISE DIAGNOSIS AND SUMMARY

Models Affected: 1988-92 GRAND PRIX MODELS

THIS BULLETIN IS BEING REVISED TO INCLUDE THE 1991 AND 1992 MODEL YEARS AND HAS BEEN EXPANDED TO INCLUDE ALL CHASSIS SYSTEMS AND ADDRESS ADDITIONAL NOISE CONDITIONS.

Some 1988-92 Grand Prix models may exhibit various noises emanating from the underbody of the vehicle that may be caused by a variety of conditions related to the various chassis systems.

It is the intent of this bulletin to summarize prior issued bulletins and to provide insight into other conditions that have been noted. To aid and insure proper diagnosing of customer noise comments, a diagnostic flow chart is provided at the end of this bulletin.

When prior published bulletins are referenced, they should be utilized to insure proper service procedures are followed.

(A) SQUEAK/SQUAWK/ITCHING NOISE -------------------------------

Condition: I ------------ Squeaking/squawking during normal suspension/vehicle operation (1988-89 Pontiac Only)

Cause:

------ Right hand park brake cable moving through non-required wire guide installed by assembly plant.

Correction:

----------- Remove non-required guide (Reference Bulletin Number 90-3-8.

Condition: II ------------- Squawking during normal vehicle operation and most prevalent in cold or wet weather (1988-89 vehicles).

Cause:

------ Auxiliary spring rubbing against edge of spring mounting bracket.

Correction:

----------- Remove auxiliary spring per procedure outlined in Service Manual and reinstall with clearance to edge of mounting bracket.

Condition: III -------------- Squeak and/or clunk noted during normal suspension movement (Early 1988 vehicles Only)

Cause:

------ Defective strut assemblies with date codes 15087-04688 (clunk) and 01688-08688 (squeak).

Correction:

----------- Replace strut dampers with the effected date codes. Any other struts that are suspected of being noisy should be bench checked per the procedure outlined in the diagnosis section of the Service Manual. Replace only those struts which exhibit excessive noise during the bench test.

Condition: IV -------------- Squawk from front of vehicle at low ambient temperatures and normal operation on 1988-90 vehicles assembled prior to VIN Breakpoint LF296738.

Cause:

------ Stabilizer shaft rotating in the power control arm stabilizer shaft insulators.

Correction:

----------- Install new high compression lower control arm stabilizer shaft insulators, P/N 10152155 (Reference Bulletin # 90-3-15).

Condition: V ------------ Squeaking during normal suspension/vehicle operation (1988-90 vehicles).

Cause:

------- Park brake cable movement through grommet in cable support brackets.

Correction:

----------- Apply lubricant to cables in area of grommets (Reference Bulletin 90-3-8).

Condition: VI ------------- Thumping/squawk noise from rear of vehicle, and most apparent when operated at low speeds over irregular road surfaces.

Cause:

------- A load spike caused by the strut jounce bumper system transmitting noise through the body strut tower structure.

Correction:

----------- Replace both rear strut jounce bumper assemblies with new assemblies contained in service unit, P/N 22063945 (Reference Bulletin 92-3-5A)

(B) THUD/CLUNK NOISE --------------------

Condition: I ------------ Thud/Clunk noise from rear of vehicle most apparent after a harsh/sharp road input such as a chuck-hole/speed bump (1988-91 vehicles with auxiliary springs).

Cause:

------ Auxiliary rear spring lower attaching bracket not in full contact with rear spindle rod.

Correction:

----------- Insure auxiliary rear springs lower brackets are properly seated on spindle rods (Reference Bulletin 91-3-18).

Condition: II ------------- Clunk noted during normal suspension/vehicle movements (1988-90 vehicles).

Cause:

------ Exhaust system contacting rear stabilizer shaft.

Correction:

----------- Inspect exhaust system and stabilizer shaft for witness marks due to metal-to-metal contact. Align exhaust system to provide adequate clearance if interference condition is noted.

Condition: III -------------- Thud noted during extended suspension movement. Condition most apparent when vehicle is turning up parking ramp/driveway or driven over deep chuckhole or speed bump (1988 and early 1989 vehicles).

Cause:

------ Rear struts extend to their maximum travel. Not detrimental to struts but associated noise may be cause of annoyance.

Correction:

----------- Replacement of both rear struts and spring plates with interim 1989 components provides additional 10 mm of travel. Component replacement will reduce the potential for occurrence of this condition but may not eliminate it completely and is inherent to suspension design (Reference Bulletin 88-3-30).

Condition: IV ------------- Thud/clunk from rear of vehicle after a harsh/sharp road input such as a chuck-hole/speed bump.

Cause:

------- Spindle rod bushing(s) loose in the spindle rod. Spindle rod cross section appears somewhat collapsed at open ends.

Correction: Replace spindle rods. -----------

Base Suspension Up Level Suspension --------------- -------------------- P/N 10062855 (Front) P/N 10062857 (Front) P/N 10152146 (Rear) P/N 10152147 (Rear)

Parts are currently available from GMSPO.

(C) RATTLE NOISE

Condition: I ------------ Metallic rattling during normal vehicle operation or engine run up in neutral (1988-90 vehicles).

Cause:

------ Loose clinch nuts in either exhaust intermediate pipe or underbody hanger brackets.

Correction:

------------ Install washer P/N 11500367 between hanger and either or both the underbody and pipe brackets.

Condition: II ------------- Metallic rattling noted during engine run-up in neutral or normal suspension/vehicle operation. (1988-90 vehicles).

Cause:

------ Loose exhaust system heat shields.

Correction:

----------- Inspect and tighten loose exhaust system heat shield fasteners insuring sufficient clearance is maintained.

Condition: III -------------- Dull rattling noted during normal suspension/vehicle operation (1988-90 vehicles)

Cause:

------ Park brake cable grommets not properly installed in underbody retaining brackets.

Correction:

----------- Insure both underbody brackets are not distorted and install cable grommets (Reference Bulletin 90-3-8).

Condition: IV ------------- Metallic rattles noted during normal vehicle operation (1991 Pontiac SE and GT coupes with "Aero Performance Package", RPO B4U)

Cause:

------ Exhaust tailpipe extensions contact rear bumper valance panel/heat shield.

Correction:

----------- Install new tailpipe extensions, P/Ns 10199291 (LH) and 10199292 (RH) (Reference Bulletin 91-6-53).

Condition: V ------------ Light hammering/rattle type noise from front of vehicle after a cold start at low ambient temperatures on 1988 vehicles assembled prior to VIN breakpoint below:

Marketing VIN Division Breakpoint --------- ---------- Pontiac JF216305

Cause:

------ Pressure pulsations in the fuel system generated by fuel injector operation, resulting in hydraulic hammering in chassis fuel pipes.

Correction:

----------- Install new underhood fuel return hose and stand-pipe assembly, P/N 10114735, (Reference Bulletin 88-6-46).

(D) OIL CANNING/POPPING NOISE -----------------------------

Condition: I ------------- Oil canning/popping noise noted during normal vehicle operation (1988-89 vehicles).

Marketing VIN Division Breakpoint -------- ---------- Pontiac KF206642

Cause:

------- Normal internal fuel tank pressure results in oil canning noise.

Correction:

----------- Replace fuel tank with new service tank, P/N 12516117, that has additional ribbing on upper and lower tank sections (Reference Bulletin 89-6-17)

Condition: II -------------- Thumping/squawk noise from rear of vehicle, and most apparent when operated at low speeds over irregular road surfaces.

Cause:

----- A load spike caused by the strut jounce bumper system transmitting noise through the body strut tower structure.

Correction:

Replace both rear strut jounce bumper assemblies with new assemblies contained in service unit, P/N 22063945 (Reference Bulletin 92-3-5A)

(E) CREAK/GROAN NOISE ---------------------

Condition: I ------------- Creak/groan or, in severe instances, a clunk/thud noise during a vehicle twisting motion maneuver such as turning up a steep incline/ driveway (1989-91 vehicles).

Marketing VIN Division Breakpoint --------- ---------- Pontiac MF235111

Correction:

------------ 1989-91 vehicles prior to above VIN breakpoints

Install new fuel tank straps, P/N 10199250 and strap spacers, P/N 10192675 (Reference Bulletin 91-6-28A).

1991 after VIN breakpoints

Install new fuel tank straps, P/N 10199250 (Reference Bulletin 91-6-28A)

(F) MOAN/BOOM NOISE ------------------- Condition: I ------------ Exhaust moan/boom 2300-2500 RPM range on 1991 vehicles with 3.4L engines (RPO LQ1) assembled prior to VIN breakpoints below:

Marketing VIN Division Breakpoint Pontiac MF262219

Cause:

------ Exhaust system excited by engine exhaust pulse induced vibration.

Correction:

----------- Install exhaust damper, P/N 10199232 (Reference Bulletin # 91-6-35)

Parts are currently available from GMSPO.

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.