How Fuel Injection Works – Direct vs Port Injectors

Today, you can no longer buy a brand new carburetor-equipped vehicle anywhere in America. However, it’s still important to know how today’s technology fuels your carb-less internal combustion engine.

Previously, gasoline engines were fed by a carburetor, which was part of the throttle body assembly. As you pressed the throttle, the butterfly valve in the carburetor would open more, which lessened the restriction on the engines cylinders to vacuum air from the outside world, through the throttle body and into the cylinders themselves.

This vacuum, also known as a draft, would subsequently pull fuel from the float bowls where it was stored in the carburetor through little needle-sized ports called jets. The jets were how fuel was metered into the intake manifold. The diameter of these jets determined the flow of fuel into the engine, along with the amount of draft passing through due to the position of the throttle body. This entirely mechanical system was pretty inefficient by current standards.

Today, carburetors have been supplanted by injection systems. These digital setups are linked through complex computer systems that inject fuel based on the timing of the engine. The computer knows the exact position of the rotating assembly inside the block, and where and when to fire the injectors. Direct injection systems are similar in application, but even more precise as the fuel is injected directly into the cylinder at incredibly high pressures (30,000 PSI+).

This video from Engineering Explained breaks down the nuts and bolts of multi-port injection that we find on the majority of engines today, as well as direct injection that is found in some higher performance gas engines and all diesel engines.