CIS=Continuous Injection System
In simple terms it means fuel is constantly flowing metered by a valve or meter. It works very well versus carburetors as there is less tuning needed.
Do a search here on CIS and read more info than you can process.
You should have CIS on your 77. It was standard starting in 74. You should get some books on 911's so you can learn as you upgrade/make repairs. 101 Projects for your Porsche 911 is an excellent source of info. A Bentley repair manual is vital to maintaining these cars, if you do the work yourself. Heck, you can understand what your wrench is telling by learning more. Hope this helps and welcome aboard.
