Engine - Intermittent Hesitation/Low Power/Rough Running
File In Section: 6E - Engine Fuel & EmissionBulletin No.: 67-65-37
Date: June, 1997
Subject:
Intermittent Hesitations, Low Power, and Rough Running Engine in Cold Temperatures (Replace PCM)
Models:
1993-95 Chevrolet and GMC, M/L, S/T Models
1993-94 Oldsmobile Bravada
with 4.3L Engine (VIN W - RPO L35) and HYDRA-MATIC M30 Automatic Transmission only
Condition
Some owners may comment about intermittent hesitations at ambient temperatures below -10°C (14°F). The hesitations may also be associated with low power or a rough running engine. This condition may lead to a closed throttle stall when stopped. This condition, if encountered, would most likely occur within the first few minutes of engine operation after a cold overnight soak. If the low power condition were encountered, the engine would run normally after one vehicle ignition cycle (Off/Start/Run).
Cause
Under certain conditions a high frequency transient voltage spike back feeds into the engine controller (PCM) and causes it to reset. PCM resets would manifest themselves as a bump or hesitation. Infrequently these resets lead to an incorrect fuel/spark run mode which is associated with the low power condition.
Correction
Replace the PCM with a new PCM. Choose the appropriate PCM from the list below.
Year Model PCM Part
1993 M/L and S/T 16245357
1994-95 M/L and S/T 16245358
In addition to replacing the PCM, the associated Memcal must also be replaced. Choose the appropriate Memcal from the listed tables.
Important:
The service Memcal is common with an EGR Service Memcal, and some vehicles may already have the correct service Memcal.
Warranty Information
For vehicles repaired under warranty, use the table.