Courtesy the
Atlas Vortec Engine Design Team under GM Engineer Mr. Ron Kociba... back in the Late 1990's ...they designed
Variable Valve Timing (0-25 Degrees of retard) into only the
Exhaust Cam Shaft side of the GM 4.2L LL8 Engine in order to improve Power, Responsiveness and Performance in a wider range of RPM.
They were wildly successful in doing so by using this Delphi Exhaust Camshaft Variable Valve Timing Phaser:
With this New Design, they were also able to eliminate the need for any
(EGR) Exhaust Gas Recycle Valve operating on this LL8 Engine. However,
the penalty was paid with the need for an Hydraulically Adjustable Cam Phaser "loosely" connected to an Internal Helical Gear that responded to an infinite range of positions within that 0-25 Degree Camshaft adjust-ability
by relying upon changes in Engine Oil Pressure. (See this Cutaway of the Design)
The Oil Filter Screens in the early Model
ACDelco and
Delphi VVT
(CPAS) Camshaft Position Actuation Solenoids tended to either get clogged with
Oil Contaminants, Dirt and Debris... or get vacuumed loose and ingested into the Engine over time. The Major Culprits or Modes of
CPAS Failure are:
(1) Lack of Frequent Oil and Oil Filter Changes.
Dirty Motor Oil is the Bane of the Cam Phaser Functioning Properly.
(2) Failed
CPAS "O" Ring Seals caused by the constant 'Action -Reaction' the inner Solenoid Plunger causes vs. the
CPAS Housing. As a result, the
CPAS Body slides
ever so slightly in and out, and it tends to Flatten Out the sealing "O" Ring" over time.
Dirty Engine Oil leaking down the Front Passenger Side of the Engine Block is the revealing symptom that this has occurred.
(3) Oil Leaks from the
CPAS Body itself contaminating the Electrical Harness Connector.