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Fuel Injector types

Fuel injectors come in many designs depending on where and how they are used. There are a couple of additional system types not mentioned here, but this will cover 95% of the gasoline injected vehicles out there to date.


Top-feed injectors have the gasoline entering from the in the top and exits the bottom. These early designs had provisions for fuel to enter through a rubber hose attached to the top. We refer to these as hose-end injectors.

Bosch hose-end JECS hose-end

Next in this category are the most common type of top-feed injectors. The use an o-ring on the fuel inlet end that slips into a fuel rail. As you can see they come in many different shapes and sizes.

small toop-feed denso top-feed2 Multec top-feed Bosch top-feed Delphi top-feed


Side-feed injectors differ since the fuel enters on the side on the injector and they actually fit inside the fuel rail and the bottom protrudes from it.

denso side-feed JECS side-feed denso side-feed2

Throttle Body Injectors

Or TBI, for short, they reside in a throttle body that is located where a carburetor used to be. Both side and top-feed injector types have been used in these applications. These are not common anymore since the injectors are moving closer to the cylinders all the time.

TBI side-feed GM TBI Starion TBI

Continuous Injection System

Or CIS injectors. The continuous fuel delivery gives the system its name. A fuel distributor changes the fuel pressure to control the volume of the fuel to be delivered under various operating conditions. These mechanical types do not clean well due to their design. They have non-removable internal filters and can't be back-flushed. Poorly performing injectors should be replaced.

CIS Injector

Gasoline Direct Injectors

Or GDI, these injectors shoot the fuel directly into the combustion chamber. These are just being used on a few engines now in the USA now. Since we don't know to any test equipment that can clean or properly test these to date, so we will just give them a mention here.