[Schulisco]

Originally Posted by porschedude996

Correct me if I’m wrong.

The Injection systems prior CIS. They were time injection by way of the pump and timing. Pump raised pressure until the injector opens and sprays into the open valve.

The CIS injectors don’t have a valve, they are wide open. Hence “Injection System”.

Small bit to clarify. The valve in the CIS injector is to prevent dripping. So wide open when engines are running.

Not fully correct, the CIS injectors are closed when engine is not running! System prior to CIS was D-Jetronic (D for german word "Druck" = pressure)
Further reading: https://jetronic.org/index.php/en/d-jetronic/51-history

Otherwise they would continue spraying after shutting down and flooding the engine until fuel accumulator and fuel lines are drained. Opening pressure of them is between 2,5 and 3,6bars as you can see in the picture.



When shutting down the engine the pressure falls under 2bars which is high enough to keep the fuel pressurized for at least half an hour to prevent building bubbles of boiling fuel due to engine heat which otherwise prevent successful hot start.

Refer to the Bosch Technical Documentation about CIS:
https://files.bmwclassic.nl/E21/K-Jet/Bosch_K-Jetronic_web.pdf

Excerpts:





You're correct in the fact that once the valves opened by the pressure they remain open as long as the pressure is high enough which produces a continuous fuel spray in front of the intake valve of every cylinder, that's why the name comes: CIS = Continuous Injection System. The fuel amount is controlled by the fuel distributor with its moving plunger by the air flow sensor plate and lever.

Thomas