Gasoline engines with throttles develop vacuum in the intake manifold. That vacuum provides information about how the engine is running and can be used to diagnose problems.
So what is vacuum, why does an engine have vacuum and how is it measured? What causes it to be high or low, what is normal? What is MAP and how does it relate to vacuum?
DISCLAIMER: In my videos and written or text comments, I provide demonstrations, suggestions, and opinions on techniques, methods, and materials for various projects. While I try to be accurate, there are no guarantees, expressed or implied, that my information is correct and will work for you. If you wish to use any of this information, you must check and verify that it is appropriate for your use use it at your risk. Doityourself projects are variable and there are risks in conducting them.