ROUGH IDLE, LACK OF POWER, MISS, HESITATION, WHISTLE

SUBJECT: ROUGH IDLE, LACK OF POWER, MISS, HESITATION, WHISTLE, LEAN ENGINE, DTC P0171, P0174, P0300, P0507 OR LOOSE UPPER INTAKE MANIFOLD BOLTS (REPLACE GASKETS AND TORQUE WITH NEW SEQUENCE)

MODELS: 1996 CHEVROLET AND GMC C/K AND P TRUCKS WITH 7.4L ENGINE (VIN J - RPO L29)

CONDITION:

SOME OWNERS MAY COMMENT OF AN ENGINE WHISTLE OR NOISE, HESITATION, LACK OF POWER OR ROUGH IDLE. THIS COULD BE ACCOMPANIED BY A LEAN ENGINE CONDITION OR HIGHER THAN DESIRED ENGINE IDLE. THE VEHICLE COULD ALSO CONTAIN STORED DIAGNOSTIC TROUBLE CODES P0171, P0174, P0300 OR P0507.

CAUSE:

THE GASKET BETWEEN THE UPPER AND LOWER INTAKE MANIFOLDS RELAXES RESULTING IN A LOSS OF BOLT TORQUE. THIS IN TURN CAN DISRUPT THE GASKET SEAL ALLOWING AN AIR LEAK INTO THE MANIFOLD ASSEMBLY.

CORRECTION:

A REVISED TORQUE SEQUENCE, TORQUE VALUES AND USE OF A THREADLOCKER ON THE UPPER INTAKE MANIFOLD BOLTS HAS BEEN ISSUED TO CORRECT THIS PROBLEM.

USE THE PROCEDURE FROM THE APPROPRIATE SERVICE MANUAL ON VEHICLE REPAIR SECTION TO REPLACE THE GASKETS BETWEEN THE UPPER AND LOWER INTAKE MANIFOLD, EXCEPT APPLY THREADLOCKER AND USE THE ATTACHED TORQUE SEQUENCE IN PLACE OF THE TORQUE SHOWN IN THE SERVICE MANUAL.

THE TORQUE VALUES AND SEQUENCE IN THE SERVICE MANUAL HAVE BEEN REVISED AND THE USE OF A THREAD LOCKER HAS BEEN ADDED. USE THE TORQUE VALUES AND SEQUENCE IN THIS BULLETIN.

BE SURE THAT ALL GASKET MATING SURFACES ARE CLEAN AND FREE FROM OIL AND RESIDUE. INTAKE MANIFOLD SHOULD BE COOL, NOT HOT BEFORE SERVICING.

TORQUE PROCEDURE:

1. COAT A MINIMUM OF 8 LOWER THREADS OF THE BOLT WITH LOCTITE(R) 242 (GM P/N 12345382) 2. TORQUE ALL BOLTS IN SEQUENCE TO 16 N.M (12 LB. FT.) 3. TORQUE ALL BOLTS IN SEQUENCE TO 24 N.M (18 LB. FT.) 4. CHECK ALL BOLTS IN SEQUENCE TO ASSURE ALL BOLTS ARE TORQUED TO 24 N.M (18 LB. FT.) 5. RECHECK BOLTS IN POSITIONS #1 AND #4 TO ENSURE THAT THEY ARE STILL TORQUED TO 24 N.M (18 LB. FT.)

PARTS INFORMATION

PART NUMBER DESCRIPTION 12527756 UPPER INTAKE MANIFOLD GASKET SET (CURRENT PRODUCTION)

12345382 THREADLOCKER LOCTITE(R) 242 (BLUE)

PARTS ARE EXPECTED TO BE AVAILABLE ON MAY 20, 1996 FROM GMSPO.

WARRANTY INFORMATION

FOR VEHICLES REPAIRED UNDER WARRANTY, USE: LABOR OPERATION: J0200 LABOR TIME: USE PUBLISHED LABOR OPERATION TIME.

FIGURES: 1 ATTACHMENTS: 0

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.

COPYRIGHT 1996. GENERAL MOTORS CORPORATION. ALL RIGHTS RESERVED.