I inherited a 99 diesel from my father in law and don't know much about them. How do you tell if there's a performance chip installed or not?

 

There are 2 kinds of performance adders. One is a plug in type performance box that would typically be located under the hood and plugged into the harness going to the injection pump. The other is an uploader to the ECM which, unless its in the consol, gonna be hard to tell.