Chevrolet Silverado / GMC Sierra. Service manual — part 1893

Fig. 43: View Of Advance And Retard Cavities
Courtesy of GENERAL MOTORS CORP.

1. Pressurized oil enters the retard cavities (2) of the actuator and moves the park pin (3) from

the locked position.

2. As pressure increases within the retard cavities (2), the rotor and camshaft rotate counter

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

clockwise retarding valve timing.

3. As the duty cycle decreases, the spool is repositioned and oil is sent to the advance cavities

(1), rotating the rotor and camshaft clockwise, advancing valve timing.

With a 0 percent duty cycle signal to the magnet, the spool is positioned in the fully
extended position and there is full flow to the advance cavities of the actuator. As duty
cycle increases to near 50 percent, flow to the advance cavities is decreased.

With a 50 percent duty cycle, the spool is positioned neutral, with no flow to either the
advance and retard cavities.

With a 51-100 percent duty cycle, the spool is positioned to provide oil flow to retard
cavities. As the duty cycle increases, the flow to retard cavities increases.

With a 100 percent duty cycle, there is full flow to the retard cavities of the actuator.

The above duty cycle percentage values are only a guideline, as the actual duty cycle
values may vary based on engine oil temperature, solenoid magnet coil temperature,
magnet coil resistance, and other specifics.

CMP Actuator Park Position Verification

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. 44: CMP Actuator Park Position Verification
Courtesy of GENERAL MOTORS CORP.

The CMP actuator can be visually inspected to determine if the tension spring has returned the
reluctor wheel and rotor to the park position.

With the reluctor wheel returned to the proper parked position, the edge of the notched area of
the wheel (2) aligns with the marking (1) on the camshaft sprocket.

CMP Actuator Handling Safety

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. 45: View Of Proper CMP Actuator Removal
Courtesy of GENERAL MOTORS CORP.

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