Aftermarket fuel injectors refer to fuel injectors produced by manufacturer who are not appointed by the manufacturer of the car. Such injector is not produced under the supervision of the car manufacturer. This is as opposed to genuine or Original Equipment (OE) which refers to the original fuel injectors fitted to the car by the car manufacturer when it left the factory.

The performance of aftermarket fuel injectors are doubtful and are usually found to be below the OE fuel injectors. A fuel injector performs such an important function without which the engine would not run. Manufacturer's fuel injector should not be replaced with a doubtful one.

The fuel injector introduces a mixture of fuel and air into the cylinder at the top of the compression stroke. The highly compressed mixture is then ignited by an electrical spark causing it to explode and produce the power that drives the engine and the car. The high precision in timing and quantity and composition of the mixtures requires a properly working injector.

Compression stroke takes only fractions of a second before turning into power stroke. The fuel and air should be mixed in correct proportions for it to burn properly. Power loss and wastage of fuel would result from delay or premature injection. For the best overall performance of your car the injector should function properly. Hard starts, rough idle, power loss during acceleration, wastage of fuel and smell of fuel in the car are indications that the injector does not function properly. Such problems are likely to be caused by aftermarket fuel injectors.

 Substandard injectors may clog easily and deteriorate quickly due to wear and tear. Such an injector will require frequent replacement leading to high maintenance costs. If made of substandard material the injector will not be able to withstand rust. The internal spring and seals of the injector may fail if made with substandard material. OE injectors are replaced after every 100,000 kilometers. Aftermarket fuel injectors may prompt replacement after much less mileage.

For cost cutting OEM injectors are recommended. OEM refers to Original Equipment manufacturers.  OEM are appointed parts manufacturers with authority from the car manufacturer. They use the design of the car manufacturer and produce the injectors under supervision of the car manufacturer. The parts are sold by the OEM packed in the car manufacturers' packaging. The OEM injector is the same as the originally installed. Bosch for instance produces OEM spark plugs for BMW, Audi, Mercedes and VW.