G 30 Van V8-454 7.4L VIN J SFI (1996)
PROM - Programmable Read Only Memory: All Technical Service Bulletins
PROM - Engine Tick/Knock/Rattle Noise
File In Section: 06 - Engine/Propulsion System
Bulletin No.: 99-06-04-014
Date: March, 1999
TECHNICAL
Subject:
Engine Tick/Knock/Rattle Noise (Reprogram VCM)
Models:
1996-99* Chevrolet and GMC C/K, G and P Models
with 7.4L Engine (VIN J - RPO L29)
*(1999 C/K, G with RPO ZK3)
This bulletin cancels and supersedes Corporate Bulletin Number # 77-61-21.
Please discard # 77-61-21 (Section 6 - Engine).
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 decel 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.
