CAM shaft position sensor

A direct-fire ignition use a synch notch on the trigger wheel to help the computer identify which cylinder is ready to fire. However, some systems use an additional sensor called a camshaft position sensor instead of a synch notch to perform this function. In this type of system, the camshaft sensor sends a signal to the computer to indicate that a particular cylinder is ready to be fired.
In most systems the camshaft position sensor is needed only when an engine is started. Once the camshaft position sensor has indicated the positions of the different cylinder to the computer, the sensor won't be needed again until the engine is shut off and restarted. However, in some systems, the camshaft position sensor may be used to directly control the operation of the ignition system or the fuel-injection system. In these engines, the camshaft position sensor provides information to the computer the entire time the engine is operating. Once the computer receives the information from its sensor, it can then decide when to fire the spark plug for each cylinder.
I hopefully wish some Mazda specialist step inn to tell you what kind of camshaft position sensor you do have in your99 Mazda B4000 p/u 4.0L.
:)

Id take care of it soon. Those are the same ones Ford uses and the bushings in the housing go bad (sounds like a belt squeek), even seen them break the housing. When you have it done be sure to have them remove the entire housing and check for any roughness of the bushing