In case of 2005 and older models, it is necessary to relieve the fuel pressure and disconnect the cable with the negative post of the battery. Take out the PCV hose at the valve cover and intake manifold. Working on a 1993 or older model, dismount the hose clamps and hoses on the air valve, unbolt the air valve and remove it on the engine side of the air intake plenum. Take care to label each injector and electrical connector with a felt pen or paint and then take out the electrical connectors and store the harness of the wire, with a small flat blade screwdriver, pressing the lock lever of each connector as you remove it. On 1997 and earlier, remove the vacuum hose at the fuel pressure regulator, disconnect the fuel lines at the fuel pressure regulator, and the fuel rail. Take out the fuel rail mounting bolts, and detach the fuel rail off the injectors. Take the mounting insulators away, pull out the fuel rail and the pressure regulator and pull out the injectors out of their bores and put them aside in a well-marked storage container that they can be reused later should they be needed. In case of using identical injectors, change the grommets and O-rings and fit the fuel injectors in the order of removal in the reverse, and then bend the fuel rail mounting bolts firmly. In 2006 and subsequent models, start by unscrewing the engine cover and depressing the system fuel pressure, this should be followed by disconnection of the cable to the negative battery terminal. Dock the quick connect fitting of the fuel supply line off of the fuel rail, then the electrical connectors off of the ignition coils and the fuel injectors, snapping the harness clips out of it and laying the harness aside. Undo the mounting bolts of the fuel rail and remove the fuel rail and injectors as a unit. Loosen up the clip holding each injector into the fuel rail and take out each injector and discard old injector O-rings. Install the new injector O-rings in lightly oiled condition, lubricate every upper O-ring with clean engine oil, and install the injectors into the fuel rail and hold them using the injector clips. Apply clean engine oil to every lower O-ring, and, being careful not to scuff the lower O-rings, put the fuel rail and injectors in place and screw the fuel rail bolts firmly. Lastly, otherwise, installation is the opposite of removal; turn on the engine and prosecute that there is no leakage.