This rather extensive article covers all aspects of the K-jetronic fuel injection systems found in E21's, such as the 318i, 320i and the 323i. Reading through these pages will help you understand how this system works, what it does, and it's individual parts.
The content of this article is a general description of the K-jetronic system, as it was used in many other cars and many other engines. Consider this as vital background information if your E21 runs with K-jetronic.