At the top of each of the forums are help full reading IE stickies (old pages or questions that stay at the top) CSP =Crank Shaft Position sensor or Cam Shaft Position sensor. Each of these sensors work with the ECM (Engine Control Module) to set the timing of each injectors and ignition. When they are not are not working you have all kinds of problems, and the ECM goes to a mode to get you home. Bad fuel mileages is a sign that something is not working right. Each of these sensors are talked about including there locations in the above mentioned stickies (stuck at the top) May be you need a shop manual?