Mercury Villager 1993-2000
Nissan Quest 1993-2000
The fuel injection system includes a high pressure electric fuel pump mounted in the fuel tank, a fuel supply manifold, a throttle body, a pressure regulator, fuel filters, and both solid and flexible fuel lines. The fuel supply manifold includes six electronically-controlled fuel injectors, each mounted directly above an intake port in the intake manifold. Each injector fires once every other crankshaft revolution, in sequence with the engine firing order.
The fuel pressure regulator maintains a constant pressure drop across the injector nozzles. The regulator is referenced to intake manifold vacuum and is connected in parallel to the fuel injectors. It is positioned on the far end of the fuel rail. Any excess fuel supplied by the fuel pump passes through the regulator and is returned to the fuel tank via a return line.
The fuel pressure regulator is a diaphragm-operated relief valve, in which the inside of the diaphragm senses fuel pressure and the other side senses manifold vacuum. Normal fuel pressure is established by a spring preload applied to the diaphragm.
The fuel system is controlled and monitored by the Powertrain Control Module (PCM), although electrical power is routed through the fuel pump relay and an inertia switch. The fuel pump relay is normally located in the fuse and relay panel under the hood, and the inertia switch is located in the passenger compartment. The fuel pump is mounted in the fuel tank.
The inertia switch opens the fuel pump ground circuit in the event of a collision or roll over. Once tripped, the switch must be reset manually by pushing the reset button on the assembly.
The fuel injectors are electro-mechanical (solenoid) type, designed to meter and atomize fuel delivered to the intake ports of the engine. The injectors are mounted in the lower intake manifold and positioned so that their spray nozzles direct the fuel charge in front of the intake valves. The injector body consists of a solenoid and ball valve assembly. The control unit sends an electrical impulse that activates the solenoid, causing the ball to move inward off the seat and allow the fuel to flow. The amount of fuel delivered is controlled by the length of time the injector is energized (pulse width), since the fuel flow orifice is fixed and the fuel pressure drop across the injector tip is constant.
The injectors receive high-pressure fuel from the fuel supply manifold (fuel rail) assembly. The complete assembly includes two tubes connected by a fuel tube hose, six fuel injector mounting flanges, the mounting flange for the pressure regulator, and mounting attachments to locate the manifold.
The fuel manifold is normally removed with the fuel injectors and pressure regulator attached. Fuel injector electrical connectors are plastic and have locking clips that must be released when disconnecting the wiring harness.
Safety is the most important factor when performing not only fuel system maintenance, but any type of maintenance. Failure to conduct maintenance and repairs in a safe manner may result in serious personal injury or death. Work on a vehicle's fuel system components can be accomplished safely and effectively by adhering to the following rules and guidelines.