Variable Camshaft Timing Solenoid And Camshaft Position Sensors

Courtesy of JAGUAR CARS, INC.

The profile, or position and shape of the camshaft lobes are optimized for a certain engine rpm, but this normally limits low-end torque or high-end power. At high engine speeds, an engine requires large amounts of air. However, the intake valves may close before all the air has been given a chance to flow in. On the other hand, if the camshaft keeps the valves open for longer periods of time, problems start to occur at the lower engine speeds. This will cause unburnt fuel to exit the engine since the valves are still open.

To overcome this, VCT changes the valve timing by either advancing or retarding the camshafts to allow for optimum engine performance, reduced emissions, and increased fuel efficiency. This is achieved via an electronically controlled hydraulic solenoid valve located in the camshaft housing at the rear of the engine, behind the rear CPS solenoid. The ECM transmits a signal to the solenoid, which directs engine oil into the VCT unit. A valve spool in the VCT unit regulates the flow of oil. Refer to Electronic Engine Controls . .

There are 2 CMP sensors located in the camshaft housing. The CMP sensors monitor the position of the camshafts to establish ignition timing order, fuel injection triggering and for accurate VCT camshaft advance-retard timing feedback.

The CMP sensor is a Hall-effect sensor, which switches a battery fed supply on and off. The supply is switched when the teeth of the reluctor pass by the tip of the sensor. The 4 teeth are of differing shapes, so the ECM can determine the exact position of the camshaft at any time. Refer to Electronic Engine Controls .