LOSS OF WIDE OPEN THROTTLE NEW CALIBRATION/ENG.THERMOSTAT

Subject: LOSS OF WIDE OPEN THROTTLE 3-4 SHIFT WHEN HOT/TULIPED INTAKE VALVES

Model and Year: 1989-91 CAPRICE WITH 4L60 AUTOMATIC TRANSMISSION AND 5.7L ENGINE

TO: ALL CHEVROLET DEALERS

THIS BULLETIN CANCELS AND SUPERSEDES DEALER SERVICE BULLETIN NO. 89-226-7A, DATED AUGUST 1989. THE 1990-91 MODELS HAVE BEEN ADDED, AS WELL AS SERVICE AND PARTS INFORMATION. ALL COPIES OF 89-226-7A SHOULD BE DISCARDED.

BULLETIN COVERS:

Service and parts information for some 1989-91 Police vehicles (5.7L "B" car). These vehicles may experience a loss of wide open throttle 3-4 upshift when hot. This can cause tuliped intake valves during extended high speed operation in third gear. An updated transmission calibration has been released to address this condition. A new engine thermostat was previously released, and should be used in conjunction with the new transmission calibration.

Drivers of Police vehicles should note that during high speed pursuit, the shift selector should be in OD (Overdrive). This maximizes powertrain performance and lessens problems that may occur during extended high engine speeds.

SERVICE INFORMATION:

The transmission service package in this bulletin may be used to service the following models of the HYDRA-MATIC 4L60:

9YNM, OBPM, 1BFM

If service is necessary on the 1 BFM model, you may not have to replace the TV boost valve and bushing. If the transmission Julian date is 267 (September 24) or later, the transmission already contains the updated TV boost valve and bushing.

Refer to Chevrolet Service Bulletin 90-2l5-6B for previously available information on a new engine thermostat.

DATE OF PRODUCTION CHANGE: (Figure 1) -------------------------- Beginning October 19, 1990 (Julian Date 292), the 1BFM model of the HYDRA-MATIC 4L60 was replaced by the 1BJM model. The 1BJM contains the updated transmission calibration.

Beginning Start of Production 1991, all Police models of the Chevrolet Caprice were built with the new engine thermostat.

SERVICE PROCEDURE: (Figure 2) ------------------ Install the TV boost valve and spring into the pump cover assembly. Install the 3-4 throttle valve, bushing and spring into the control valve assembly. Follow the procedures listed in the Automatic Transmission Unit Repair Section of the applicable Service Manual.

IMPORTANT: Do not install a 1991 model transmission into a 1989 or 1990 vehicle. Part changes made in the 1991 model year make the 1991 models incompatible with earlier vehicle systems.

SERVICE PARTS INFORMATION:

Description Part Number ------------ ----------- Police Package 8673948 (Includes: TV boost valve and bushing, 3-4 throttle valve, bushing and spring)

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.