Engine - Detonation or Idle Roughness

91chevy13

Number: 91-274-6E

Section: 6E

Date: APRIL 1991

Corp. Bulletin No.: 136507


Subject: COLD ENGINE OR HOT ENGINE RESTART DETONATION OR IDLE ROUGHNESS DUE TO LEAN CONDITION


Model and Year: 1990-91 S TRUCK


Condition: Some owners of 1990 and 1991 S trucks with 2.5L engines (VIN Code E) may comment of an engine detonation or idle roughness when cold or after a hot restart.

Cause: The production calibration has a temporary lean condition when the engine is cold or after a hot restart.

Correction: New MEMCALS have been released which address this temporary lean condition. Install the correct MEMCAL from the chart below:

Trans Axle MEMCAL
Model Engine P/N Code I.D. Broadcast Scanner

"S" 2.5L LN8 MAN 5 SPD 3:73 16159046 AXAA 9041
"S" 2.5L LN8 MAN 5 SPD 4:11 16159047 AXAB 9051

Parts are currently available from GMSPO.

Labor Operation Number: T0500

Labor Time: 0.7 Hours

Trouble Code: 92