ENG. STALL AFTER HOT RESTART/ COLD START & COLD ENG. HES.

MODELS AFFECTED: 1987-88 CENTURYS WITH LB6 2.8L V-6 ENGINES (VIN CODE W) 1988 REGALS WITH LB6 2.8L V-6 ENGINES (VIN CODE W)

This revision changes the bulletin section, models affected, and recommended procedures and replaces dealer service bulletin 87-6B-2, which should be discarded.

Some 1987 Centurys equipped with a 2.8L MPFI V-6 engine may experience a cold start stall, a stall after start with a warmed-up engine or a stall during deceleration. Some 1988 Centurys and Regals equipped with 2.8L MPFI V-6 engines may experience a cold start stall.

A repeated stall after hot restart may be caused by residue accumulating inside the throttle body bore, behind the throttle plate, which limits the air flow past the throttle plate in the idle position. The hesitation concern may be due to a lean Electronic Control Module (ECM) fuel calibration. The cold start stall may be due to a lean ECM calibration, low engine idle speeds, the loss of fuel pressure, or loose electrical connections at the ignition coil and/or the mass airflow sensor.

Customer comments may be repaired as follows:

1. Perform normal service procedures as outlined in the shop manual for the repair of engine stall or hesitation.

2. Verify that all electrical connections such as at the ignition coil and mass airflow sensor are secure.

NOTICE: LOOSE/POOR ELECTRICAL CONNECTIONS AT ALL SENSORS AND METRI-PAK CONNECTORS ECM CAN BE A PROBLEM ANYWHERE ON THE ENGINE. INTERMITTENT CONNECTION CAN PRODUCE STALLING.

3. Verify that there are no engine vacuum leaks at the manifold absolute pressure (MAP) sensor, positive crankcase ventilation (PCV), exhaust gas recirculation (EGR), or other systems.

4. Verify that the fuel system is functioning properly and has proper fuel pressure.

5. Clean the throttle body bore as specified in Dealer Service Bulletin 87-6E-15A (1987 Century Only).

6. Measure the minimum idle speed and adjust to specification if required (reference Dealer Service Bulletin 87-6E-15A) (1987 Century Only).

7. Measure the Throttle Position Sensor (TPS) voltage and adjust to 0.62-0.67 volts, if required.

8. Replace the ECM MEMCAL (see Chart) using the following installation procedure (1988 Centurys and 1988 Reaals after VIN J1402629 already have the new memcal installed in production):

(a) Disconnect battery power. (b) Install new ECM MEMCAL calibration. (c) Reconnect battery power. (d) Start vehicle with AC/defroster off and power steering not cramped. (e) Allow vehicle to idle in drive for 6 minutes and until thermostat has opened. This will facilitate learning of base idle. (f) Return vehicle to service.

NOTICE: DO NOT REPLACE THE MENCAL AND RETURN THE VEHICLE TO THE CUSTOMER WITHOUT PROPERLY COMPLETING THE PREVIOUS SERVICE INSTRUCTIONS (ITEMS 1-7).

1987 CENTURY MEMCAL CHART (ALL 1988 CENTURYS SHOULD HAVE THE NEW MEMCAL) ---------------------------------------------- Emission Part Memcal Model Trans. Ratio System Number Scanner ID ----- ------ ----- ------ ------ ---------- Coupe/Sedan Auto-3 2.84 Federal 16087135 6901 Coupe/Sedan Auto-3 3.18 Federal 01228601 8601 Coupe/Sedan Auto-4 3.33 Federal 16087075 6941 Wagon Auto-3 3.18 Federal 01228609 8609 Wagon Auto-4 3.33 Federal 16087057 7001 Coupe/Sedan Auto-3 2.84 California 01228599 8599 Coupe/Sedan Auto-3 3.18 California 01228603 8603 Coupe/Sedan Auto-4 3.33 California 01228607 8607 Wagon Auto-3 3.18 California 01228611 8611 Wagon Auto-4 3.33 California 01228615 8615

1988 REGAL MEMCAL CHART (FOR REGALS BELOW VIN J1402630)

Emission Part Memcal System Number Scanner ID ------ ------ ---------- Federal 16087003 7131 California 16087012 7151

WARRANTY INFORMATION

Use applicable labor time and operation numbers.

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.