F 250 4WD Super Duty V10-6.8L VIN Z CNG (2003)
Variable Cam Timing (VCT) Solenoid Valve
The VCT solenoid valve (Figure 131) is an integral part of the VCT system. The solenoid valve controls the flow of engine oil in the VCT
assembly. As the PCM controls the duty cycle of the solenoid valve, oil pressure/flow advances or retards the cam timing. Duty cycles near 0% or
100% represent rapid movement of the camshaft. Retaining a fixed camshaft position is accomplished by dithering (oscillating) the solenoid valve
duty near 50%.
Variable Cam Timing (VCT) Unit Assembly
Variable Cam Timing Unit Assembly
The VCT unit assembly (Figure 132) is coupled to the camshaft through a helical spline in the VCT unit chamber. When the flow of oil is shifted
from one side of the chamber to the other, a pressure differential occurs forcing the piston to move. This movement is translated into rotational
camshaft motion through the helical spline coupling. A spring installed in the chamber is designed to hold the camshaft in the minimum overlap
position (5 degrees) when oil pressure is too low to maintain adequate position control.