140604004A

File in Section:
Bulletin No.:
Service Bulletin
Date:
06 - Engine
14-06-04-004A
April, 2014
INFORMATION
Subject:
Various Engine Noises During Cold Start and Warm Engine Operation
Models:
2014 Chevrolet Corvette
2014-2015 Chevrolet Silverado 1500
2015 Chevrolet Suburban, Tahoe
2014-2015 GMC Sierra 1500, Denali Models
2015 GMC Yukon, Yukon XL
Equipped with 4.3L – RPO LV3, 5.3L – RPO L83, 6.2L – RPO L86 or 6.2L – RPO LT1
This Bulletin has been revised to remove the Split Pulse Injection information section and
add the Model Year 2014 Corvette. Please discard Corporate Bulletin Number 14-06-04-004.
Information For Why New Engine
Technologies Are Generating Noises
The latest generation of full size trucks and utilities
incorporate a new generation of technologies not
previously seen in full size truck and utility applications.
As a result these engines generate noises during cold
start and during warm operation that owners of
previous generation multiport fuel injection (MFI)
vehicles may not be familiar with.
Direct Injection (DI) / High Pressure
Fuel Pump / Fuel Injectors
The new Small Block Generation 5 engine family
incorporates a new fuel system technology known as
Direct Injection (DI). With DI, fuel is injected directly into
the cylinder using a high pressure fuel system. DI
provides many benefits in improving engine
efficiency. In particular, DI improves power, torque, and
most importantly fuel efficiency. This technology is
included as standard equipment on all Generation 5
engines in the Small Block engine family which are
the: 4.3L V6, 5.3L V8, and 6.2L V8.
The high pressure fuel system does have unique
operating characteristics, in particular the noise
emanating from the high pressure fuel pump can result
in a subtle ticking noise that is apparent when the
vehicle is idling. The sound is more evident when
outside around the vehicle, when the hood is open or
the vehicle is operated in a drive-through. The sound
may be more noticeable during a cold start, but lessens
once the engine is warm. A slightly higher pitched
clicking sound is the fuel injectors pulsing ON and OFF
under the high fuel pressures. These sounds are a
normal characteristics of the DI high pressure fuel
system.
Another operating characteristic is a slightly longer
crank time when the engine is started. The increased
crank time is the result of the time required to build high
pressure in the fuel system before the engine starts.
Oil Pump Cold Start Rrrrp or Rasp
The oil pump design has changed from a gerotor gear
type pump to a two speed vane type pump for fuel
economy reasons. At temperatures of 32°F (0°C) or
colder, when the engine has been sitting for a few hours
it is possible to have air enter the pump through normal
oil drainback. Upon startup the owner may hear a short
Rrrrp or Rasp coming from the front of the engine. It is
most often heard during a remote start. There is nothing
wrong with the oil pump or oil system. No repairs
should be attempted for this condition.
GM bulletins are intended for use by professional technicians, NOT a "do-it-yourselfer". They are written to inform these
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 your GM dealer for information on whether your vehicle may benefit from the
information.
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