Caprice Wagon RWD V8-305 5.0L (1991)
PROM - Programmable Read Only Memory: Customer Interest
A/T - Loss of Wide Open Throttle 3-4 Shift When Hot
Number: 91-164-7A
Section: 7A
Date: January 1991
Corporate Bulletin No.: 077155
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, 0BPM, 1BFM
If service is necessary on the 1BFM 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 90-215-6B for previously available information on a new engine thermostat.
Figure 1 - HYDRA-MATIC 4L60 Transmission Identification Information
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.
