The camshaft interrupter magnet is a strong little magnet in a plastic holder (in some 3800s) that snaps into the camshaft gear from the BACKSIDE. To find out if yours is bad (usually, gone) get a telescoping mirror and pull the cam sensor pickup back out of its hole. Then shine a light on the mirror in front of the hole so the light goes in the hole and turn the engine over by hand with a big wrench. You will eventually see the magnet (good) or the hole it fits into (not as good) If it is gone or broken, you will have to remove the timing cover to install the new one $7 at O 'Reilly'* for the plastic version.
If you don't have one, get the Haynes or Chilton'* manual for your car. This is not a difficult job, but it will take you several hours.