Fuel Injector: Description and Operation

5-Cylinder Intake Manifold Assembly Showing Throttle Body And Injectors:

Air Shrouded Fuel Injector (All W/CIS):

CIS injectors are pressure operated valves that open only when the pressure inside excedes a preset minimum (approx. 63 - 67 psi/4.3 - 4.6 bar). When the engine is running, fuel pressure in the lines is always higher than the minimum opening pressure of the injectors. The quantity of fuel injected is regulated in the fuel distributor rather than by the injectors themselves. When the engine is turned "OFF", fuel continues to flow until the pressure drops slightly below the minimum opening pressure of the injectors. Retaining fuel pressure in the injectors and lines helps to reduce the tendency for fuel percolation and provides for easy starts, especially during hot re-starts.

All injectors are now air shrouded. Measured air is directed to a passage in the intake manifold where it flows through an insert installed with the injectors. During the intake cycle, the air swirls around the injector tips. This helps improve engine response and driveability through better fuel atomization, especially with low airflow velocities that occur during idle and low speed/part throttle operation.

This is the second generation of air shrouded injectors. They can be distinguished from older type injectors by the circlip holding the sealing O-ring in place, the use of a brass insert and plastic injector shroud, and by the fluted directional air shield attached to the tip of the injectors (not used on the old style injectors). Old and new style air shrouded injectors are not directly interchangeable. The new style injectors and inserts must be used together, however, the entire assembly (inserts and injectors) can be installed in engines of older vehicles that used the old style air shrouded injectors. Neither type can be used in older engines that did not come with air shrouded injectors.