Install and remove engine fuel injectors in 4-cylinder engines First, relieve the fuel system pressure, then dismount the air chamber, loosen the vacuum hose and fuel lines and disassemble the pressure regulator and fuel rail assembly. Un-hook the injector wiring and remove the injectors, removing the grommets and O-rings. To install, follow the steps reversed, making sure to tighten the fuel rail bolts to 15 ft.lbs. (20Nm) and with new O-rings covered with clean engine oil. In the case of a 3.0L engine, remove the injector harness, invert the fuel rail assembly, take off the lock rings, and remove the injectors. When using injectors that are in reuse, limit the openings to avoid contamination, lubricate fresh O-rings with engine oil and assemble the injectors into the fuel rail receiver cups, put in the lock rings later. In an engine with a capacity of 4.0L, unscrew the negative battery cable, discharge pressure of the fuel, and take off the upper intake manifold and throttle body assembly. Take off the fuel supply manifold, then take off the injector retaining clips and injector discarding the O-rings. Check the injector caps and change them in case of necessity. Apply clean light-grade oil to new O-rings and install them on the 2 injectors and the injectors are then installed carefully with a twisting motion. Install the fuel supply manifold making sure that the O-rings are placed in place then the upper intake manifold and throttle body assembly. Once installed, re-connect the negative battery cable, press the ignition ON to pressurize the system and leaks. Lastly, install the injector wire connectors and the vacuum line, attach the air inlet tube and restart the engine and again check the leakage. To test, disconnect the engine wiring harness connector to the injector, place a Digital Volt-Ohmmeter (DVOM) to probe into the connector and set the meter to a resistance value from 12-16 ohms, then check the resistance of the injector, which is expected to be within this range, a value 12-16 ohms; otherwise the injector is compromised and should be replaced.