There’s a fairly concise article on Wikipedia that describes the fundamentals and evolution of the Bosch Jetronic systems https://en.wikipedia.org/wiki/Jetronic
There you’ll also find a reference link to a more detailed writeup on D-Jetronic History and Fundamentals

Google “jetronic images” and you’ll find all kinds of schematics and pics to go along with that. Click/tap on the images to take you to all kinds of interesting sites, some more Volvo specific.

The new fangled D-Jet injection system as used on the Volvo 140E, 164E/ES and 1800E/ES series in the early 1970s quickly gained a reputation for being a bit trouble prone, leaving a few owners I knew pining for their previous SU carbed Amazons. By the time I was ready to trade in my beloved 122S, Volvo had just come out with the first iteration of the purely mechanical K-Jet system (called CIS then) in my shiny new 1974 144GL, an extremely reliable car by comparison to the 1971 and 1972 142E my business acquaintances had that I often got to ride in.
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Dave -still with 940's, prev 740/240/140/120 You'd think I'd have learned by now