feeler gauge: A device for measuring the distance, or gap, between two surfaces, such as between the center and side electrodes on a spark plug.

firing order: The sequence in which the cylinders fire on a particular engine to distribute the shock of combustion evenly and to reduce engine vibrations.

fuel filter: A device that removes impurities from the fuel before it gets to the fuel injection system. In fuel-injected cars, the filter is found either in the fuel line under the car, or mounted on the firewall.

fuel injection: A fuel system without a carburetor that employs an electronic fuel management system to deliver a specific amount of fuel to each combustion chamber in response to changes in engine speed and driving conditions.

fuses: Fuses protect the electrical components and wiring on your vehicle the same way they do in your home. They’re located in a fuse box (or boxes) that usually are found under or near the dashboard or under the hood.