Fuel injectors operate in conjunction with a high pressure fuel system. The fuel injector head is connected to the fuel line and engine through a O-ring seal. The O-ring allows the injector to be seated, in both the fuel line and engine, without requiring bolts, screws or threaded connectors. Injector leaks stemming from poor O-ring connections may be caused by O-ring shrinkage, exposure to high heat, chemical decomposition, or tears in the O-ring material. Leaks coming directly from the injector require full injector replacement. Replace O-rings whenever an injector is removed from the fuel line or engine, for best results.
Pressurise the fuel system by turning the ignition key to the "electronics only" mode. The fuel pump will turn on pressurise the fuel lines. If in doubt, turn on the vehicle briefly.
Lift the bonnet. Inspect the fuel injectors and connections for leaks. If fuel is leaking from the injector seal at the fuel line -- the point at which the injector connects to the fuel rail -- the leak is most likely due to O-ring failure. If the fuel is leaking directly from the injector, the injector needs to be replaced. Fuel leaks inside the engine's cylinders, often reported by the on-board computer as lean or rich conditions, will require injector replacement.
Depressurise the fuel system. Remove the plug to the fuel safety cut-off switch, if equipped, to disable the fuel pump. Fuel safety cut-off switch locations can be found in the vehicle's owner's manual. Attempt to start the vehicle several times to use any remaining fuel. Remove the ignition key and disconnect the battery.
Remove any vehicle components restricting access to the fuel line. Air intakes, electronics, vacuum hoses and components should all be carefully labelled to ensure they are correctly reinstalled when you are finished servicing the vehicle. Disconnect the fuel injector plug.
Disconnect the fuel rail from the fuel injector. Some fuel rails are bolted to the engine. Remove any bolts which prevent removal of the fuel rail. Pull the rail directly away from the fuel injector to disengage the seal. A small amount of fuel may spill from the rail, once the rail is lifted from the injector. Wipe up any fuel before continuing.
Grasp the injector with your hands, to avoid tool damage to the injector, and pull directly away from the engine to remove the injector. Rock the injector if the seal is tight. You may feel a slight popping sensation when the injector releases.
Inspect the fuel injector for physical damage. Cracked or damaged injectors should be replaced.
Remove the O-rings from the top and bottom of the injector. Clean the injector head and nozzle with a brake parts cleaner saturated cloth and allow to dry.
Install new O-rings on the removed injectors. Coat the O-rings with a small amount of motor oil. The motor oil will lubricate the O-rings during installation to help prevent small tears during the seating process and help prevent the breakdown of the O-ring during use. Slide an O-ring over each end of the injector until the O-ring is seated in the gap provided for the seal.
Grasp the injector with your hand and push the injector into the injector hole on the engine. You may feel a small pop as the injector becomes seated. When correctly installed, the injector will resist removal.
Press the fuel line onto the injector head, until it is firmly seated.
Reconnect the fuel injector plug. Reattach the fuel rail to the engine, if required. Connect any engine components initially removed to provide access to the fuel injectors. Connect the battery.
Reconnect the fuel safety cut-off switch, if disabled. Turn on the vehicle for 15 seconds to allow the fuel lines to pressurise. Check for leaks. Start the vehicle to confirm installation.
If your vehicle is not equipped with a cut-off switch, to remove fuel pressure, disconnect the battery and unplug a fuel line. Catch any fuel in a container and then reconnect the fuel line. It may be necessary to remove a the rail from several injectors, especially with metal fuel rails, to allow access to the leaky injector. Have enough O-rings on hand as replacements for any injectors requiring removal. Some engines require all the injectors to be seated in the engine before fuel rail attachment. If this is required, install all injectors prior to attaching the fuel rail to avoid disconnecting a newly installed injector. Wear Nitrile gloves to avoid contact with fuel; latex gloves deteriorate when exposed to gasoline.
Clean only the O-ring seal area with the brake parts cleaner saturated cloth. Areas other than the O-ring seal seat may have a protective coating that may dissolve in contact with solvents.