Q: How to service fuel injectors and Fuel Rail on a Nissan Quest?A: The fuel injectors on the front bank can be serviced without removing the upper intake manifold. However, servicing the fuel injectors on the rear bank requires removal of the upper intake manifold. It is not necessary to remove the fuel rail if you're only servicing a fuel injector. Fuel injectors can be removed without detaching the fuel rail. First, relieve the fuel pressure. Then, disconnect the cable from the negative terminal of the battery. Remove the air intake plenum (upper intake manifold) from the lower intake manifold. Disconnect the fuel injector connectors. If servicing of the fuel injector(s) is necessary, remove the injector cap screws and cap, then pull the injector(s) from the fuel rail cup. Inspect the injector 0-rings (three per injector) for signs of deterioration. Replace as required. Lubricate the new 0-rings with light grade oil. Do not use silicone grease. It will clog the injectors. Using a light twisting motion, install the injector(s) into the fuel rail cup. Ensure that the injector caps are clean and free of contamination and tighten the cap screws. If removal of the fuel rail assembly is necessary, disconnect the fuel feed and return lines then remove the fuel rail retaining bolts (two on each side). Using a rocking, side to side motion, carefully lift the fuel rail and the fuel injectors as an assembly from the lower intake manifold. Installation is the reverse of removal with the following exceptions: Inspect the fuel rail insulators (one per injector) for signs of deterioration and replace as required. Install the fuel rail insulators into the lower Intake manifold and lubricate them with a light coat of oil before installing the fuel rail assembly onto the lower intake manifold.