SQUEAK/SQUEAL AFTER COLD START (INSTALL REDESIGNED OIL PUMP)

SUBJECT: SQUEAK/SQUEAL NOISE AFTER COLD START

MODELS AFFECTED: 1991-1993 MODELS WITH 4.5L, 4.9L V8 ENGINE(VIN 8 0R VIN B)

Some 1991-1993 vehicles equipped with either the 4.5L or 4.9L V8 engine may experience a squeak or squeal type noise as the engine is started from a cold condition (sometimes misdiagnosed as belt squeal). The noise lasts for a few minutes then disappears and may or may not return during the next cold start. This noise is not exhibited once the engine is warm and may be more frequent and longer lasting during colder ambient temperatures.

The source of this noise is a rapid oscillation of the pressure relief valve (non-serviceable) inside the oil pump. An oil pump with a redesigned relief valve has been developed to alleviate this condition. The new pump, P/N 3535211, went into production in October, 1992 effective with EUNTlOL520897 located on the inside of the rear valve cover and is currently available from GMSPO to address complaint vehicles. The revised pump supersedes the previous design part number 1649416. For 1991-1993 vehicles only.

Parts are currently available from GMSPO.

WARRANTY INFORMATION VEHICLE SERIES Operation Operation Description Number c D E K v

Pump, Engine Oil - Replace J1020 1.6 1.8 1.8 1.9 INC: R&R oil pan ADD: B- To clean parts on vehicles over 30,000 miles if necessary .2 .2 .2

Part Group: 1.652 Policy: T

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.