Engine - Stall After Hot Restart/Cold Start

9222buick01

Bulletin
88-6E-25

Date
Jan., '89

Ref. No.
88-046A-6E

Corp. Ref. No.
836502R


SUBJECT:
ENGINE STALL AFTER HOT RESTART/COLD START, AND COLD ENGINE HESITATION

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 ECM METRI-PAK CONNECTORS 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 Recals 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 MEMCAL 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)





MEMCAL CHART


WARRANTY INFORMATION

Use applicable labor time and operation numbers.