Mazda Miata fuel injectors are located in the intake manifold. Holes for the fuel injectors are located in the intake runner of the manifold adjacent to each intake valve. Fuel is supplied to the injectors through a metal fuel rail. The injectors are plugged into the fuel rail, which sandwiches the injectors between the rail and the intake manifold. An electric fuel pump in the fuel tank supplies fuel pressure to the injectors.
Remove the air cleaner and all the plastic air ducts to the throttle body using the screwdriver. Remove the fuse for the electric fuel pump. The fuse block is on the driver's side fender well. If the fuses are not marked, look for a fuse diagram in the owner's manual. Location may be different for different years.
Crank the engine over for two seconds to relieve the fuel pressure. Turn the key off. Replace the fuse to the fuel pump.
Disconnect all the electrical connectors on the fuel injectors. Remove the bolts that secure the fuel rail to the intake manifold, using the appropriate socket and ratchet. Pry the fuel rail up carefully, withdrawing the fuel injectors from the intake manifold. Pull the fuel injectors out of the fuel rail.
Inspect the new fuel injector and make sure that it has an O-ring on the top and the bottom. Push the fuel injector into the fuel rail until you feel the O-ring snap into its pocket in the rail. Make sure that the electrical connector is facing in the right direction and can be plugged in.
Align all the injectors carefully with their corresponding holes in the intake manifold. Push the fuel rail down slowly while continuously aligning the injectors with their pockets in the manifold. When all the injectors begin to enter the manifold, give a good push to snap them into the manifold. Install the hold down bolts on the top of the fuel rail. Tighten the bolts, drawing the fuel injectors the rest of the way down. Connect all the fuel injector electrical connectors.