7.4L Eng Tick/Knock/Rattle Noise - Reprogram VCM (99-06-04-014)

Publication date: 1999-03-01
Reference number: 99-06-04-014

7.4L ENG TICK/KNOCK/RATTLE NOISE - REPROGRAM VCM

TECHNICAL SERVICE BULLETIN

Reference Number(s): 99-06-04-014, Date of Issue: March, 1999
Superceded Bulletin(s): 77-61-21

ENGINE TICK/KNOCK/RATTLE NOISE (REPROGRAM VCM)

Model(s): 1996-99 Chevrolet and GMC C/K, G and P Models

Section: 06 - Engine/Propulsion System

Bulletin No.: 99-06-04-014

Date: March, 1999

NOTE: This bulletin cancels and supersedes Corporate Bulletin Number #77-61-21. Please discard #77-61-21 (Section 6 - Engine).

VEHICLES AFFECTED

1996-99 Chevrolet and GMC C/K, G and P Models w/ 7.4L Engine (VIN J-RPO L29) - (1999 C/K, G w/ RPO ZK3).

CONDITION

Some owners may comment about a light tick or knock noise that resembles either a valve lifter tick/rattle or a piston or piston pin slap. The condition will be most noticeable on cold start. This noise can be present upon engine decal after initial starting flare and may not be consistently repeatable.

CAUSE

On the initial cold start under certain low temperature conditions, the engine RPM flare may cause the piston to tip while at top dead center. This tipping allows the small carbon deposits above the top ring land to contact the inside of the cylinder bore making a light tapping noise. While this is not detrimental to the performance, durability or ability of the engine to meet emissions standards, it is an undesirable audible noise condition.

CORRECTION

A new engine calibration has been developed for the 1998 and 1999 model year vehicles built before August of 1998. A new calibration for the 1996 and 1997 model year vehicles is being developed and this bulletin will be re-issued as soon as that information is available. The new calibration reduces the idle flare in terms of maximum RPM and length of time the flare occurs allowing the seconds necessary for thermal expansion of the piston in the bore.

PARTS INFORMATION

There are no physical parts to be installed. Reprogram the VCM with the appropriate calibration from the table below.

PARTS INFORMATION

Old P/N	New P/N	Application
16249494	09364742	G Van with L29 & MT1 & NB6
16249495	09364743	G Van Cutaway with L29 & MT1 & NB6
16249496	09364744	G Van with L29 & MT1 & NF2
16249462	09364781	P Truck with L29 & MT1
16249523	09364773	C/K Truck with L29 & MT1 & NB6-ZM9 L29 & MT1 & E62/E63 & NB6
16249524	09364774	C/K Truck with L29 & MT1 & NF2-NM8/ZM9
16249525	09364775	C/K Truck with L29 & MW3 & NF2-NM8/ZM9
16259047	09364778	C/K Truck with L29 & MW3 & NB6 & ZW9
16259048	09364779	C/K Truck with L29 & MT1 & NB6 & ZW9
16259051	09364802	C/K Truck with L29 & MT1 & NF2 & NM8
16259052	09364803	C/K Truck with L29 & MW3 & NF2 & NM8

The calibrations mentioned above are available on 1998 Techline CD 13 or newer.

WARRANTY INFORMATION

For vehicles repaired under warranty, use:

WARRANTY INFORMATION

Description	Labor Operation	Labor Time
PROM - Reprogram On Car	J6355	Use published labor operation time