STALL,TIP-IN HES. AND/OR STORED ENGINE CODES (PROMS)

MODELS AFFECTED: 1987-88 CENTURY WITH 2.8L ENGINE (VIN CODE W) 1988 REGAL WITH 2.8L ENGINE (VIN CODE W)

This bulletin has been revised to change the MEM-CAL part number for the 1988 Regal with 4-speed automatic transmission and California emission and to change the last paragraph regarding additional information after changing the MEM-CAL. Please discard Buick Bulletin 88-6E-30 and replace it with this Bulletin, 88-6E-30A.

Some customers with an engine/vehicle combination listed below

1988 Regal with a 2.8L engine (Vin Code W), and 1987-88 Century with a 2.8L engine (Vin Code W),

may comment that they have experienced one or more of the following conditions:

A cold start stall or sag,

A decel stall,

A tip-in hesitation, or

A check engine light with stored Codes 23, 25., 33, or 34.

These conditions may be attributed to a number of components/interactions. In the interest of simplifying diagnosis and repair, the following procedure has been developed to reduce system sensitivity, thereby addressing a variety of potential causes simultaneously.

If a customer comment concerning an occasional engine stall or a drive hesitation is received, and/or a stored Code 33 or 34 is found, then complete the following procedure:

1. Perform diagnostic procedures per Section 6E of the Service Manual, and correct any faults except for Codes 33, 34, 23 or 25. If the diagnostics indicate the Mass Air Flow (MAF) is to be replaced or a Code 33 or 34 is present, DO NOT REPLACE THE MAF SENSOR! Proceed to Step #3. If a Code 23 or 25 is present, go to Step #2 below. PROCEED TO STEP #3 ONLY IF NORMAL DIAGNOSTIC CHECKS DID NOT IDENTIFY A CAUSE FOR THE CUSTOMER CONCERN.

2. If a Code 23 or 25 is stored, perform the model year diagnostics for the Manifold Air Temperature Sensor (MAT). If the diagnostics indicate that the MAT is faulty and replacement is required, replace the combination MAT/MAF sensor. Proceed to Step #3.

3. Install a new MEM-CAL into the Engine Control Module (ECM) per instructions below. The new MEM-CAL is available from GMSPO. See attached service part number chart. Install the identification label package to the ECM access door and to the left shock tower per label kit, part number 10154725 instructions.

IMPORTANT: The new MEM-CAL to be installed does not need or use the existing MAF signal; however, it does need and use the MAT signal.

A). Pull the underhood ECM continuous power fuse or disconnect the battery and leave it disconnected for at least 10 minutes.

B). Remove MAF relay, if applicable, and discard. Tape up connector to prevent water intrusion.

C). Remove current MEM-CAL and install a new service MEM-CAL.

D). Restore the battery power and place air conditioning controls (if equipped) in the "off" position.

E). Firmly apply the parking brake and block the drive wheels. Start the engine, and shift the transaxle to "drive."

F). Allow the engine to run until the engine cooling fan has cycled once, or a maximum of 10 minutes.

G). Turn the ignition key to the "off" position for at least 5 seconds.

H). Start the engine, and shift the transaxle to "drive."

I). Allow engine to run for at least 5 minutes.

After a MEM-CAL replacement, the 1987-88 2.8L Speed Density Engine Driveability and Emissions Manual, ST399-87/88 SDM, must be used for Driveability and Emissions Diagnostics. To secure additional publications, use order forms available to all dealers through Helm, Inc., or dial (313) 865-5000 and ask for Customer Service.

Use applicable labor operations and times.

Labor Operation Number: J5670 for MAF/MAT replacement. Labor Operation Number: T1492 for MEM-CAL change, as follows:

1987/88 Century = 1.0 Hour

1988 Regal = 0.8 Hour

Trouble Code = 92

MEM-CAL SELECTION CHART - SERVICE PART NUMBERS

IMPORTANT: MEM-CAL MUST BE ORDERED WITH LABEL KIT, P/N 10154725

MODEL MODEL EMISSION MEM-CAL SCANNER BROADCAST YEAR TYPE TRANS. CONFIG. PART NO. I.D. CODE ---- ---- ------ -------- -------- ----- ---- 87-88 Century AUTO 3-SPD FED 16140346 0421 ASMT 88 Regal AUTO 4-SPD. FED 16141562 1621 ASWH 87-88 Century AUTO 4-SPD. FED 16140347 0431 ASMU 87-88 Century AUTO 3-SPD. CAL 16140348 0441 ASMW 88 Regal AUTO 4-SPD. CAL 16145947 5971 ATRA 87-88 Century AUTO 4-SPD. CAL 16140349 0451 ASMX

Parts are currently available through 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.