Chevrolet Silverado / GMC Sierra. Manual — part 1891

The CMP actuator is a vane type design that hydraulically changes angle or timing of the
camshaft relative to crankshaft position. The CMP actuator allows earlier or later intake and
exhaust valve opening during the 4-stroke engine cycle. The CMP actuator cannot vary the
duration of valve opening or valve lift. The CMP actuator is to be serviced as an assembly. For
system operation, refer to Camshaft Actuator System Description .

The CMP actuator consists of the CMP reluctor wheel (1), wheel retaining pins (2), return spring
(3), front cover (4), park position pin (5), park position pin spring (6), vanes and vane springs
(7), rotor (8), housing with chain sprocket (9), sealing cover/thrust plate (10), and bolts (11).

CMP System Operation

Fig. 38: CMP Actuator
Courtesy of GENERAL MOTORS CORP.

A CMP actuator dynamically changes valve timing events relative to piston timing by controlling
camshaft position. This is sometimes referred to as variable valve timing or camshaft phasing.
Variable valve timing or camshaft phasing does not change duration or lift.

By advancing camshaft timing, an improvement in low end torque can be achieved.

By retarding camshaft timing slightly, an improvement in high end power can be achieved.

By retarding camshaft timing significantly, an improvement in light load fuel economy can
be achieved.

There are 5 cavities divided by vanes within the CMP actuator.

2008 Chevrolet Silverado 1500

2008 ENGINE Engine Mechanical - 4.8L, 5.3L, 6.0L, 6.2L, or 7.0L - Cab & Chassis Sierra, Cab & Chassis Silverado,

Sierra & Silverado

When oil is directed to the advance cavities (1), the camshaft timing is advanced.

When oil is directed to the retard cavities (2), the camshaft timing is retarded.

When oil is directed to both cavities, the camshaft is held stationary.

2008 Chevrolet Silverado 1500

2008 ENGINE Engine Mechanical - 4.8L, 5.3L, 6.0L, 6.2L, or 7.0L - Cab & Chassis Sierra, Cab & Chassis Silverado,

Sierra & Silverado

Fig. 39: Timing Camsghaft - 62 Degree Range Of Authority
Courtesy of GENERAL MOTORS CORP.

The 6.0L L76 and 6.2L L92 CMP actuator has a 62 degree range of authority. With the engine

2008 Chevrolet Silverado 1500

2008 ENGINE Engine Mechanical - 4.8L, 5.3L, 6.0L, 6.2L, or 7.0L - Cab & Chassis Sierra, Cab & Chassis Silverado,

Sierra & Silverado