Ford Aerostar 1986-1997 Repair Guide

General Information


See Figure 1

The electronic fuel injection (MFI) system used on the 2.3L, 3.0L and 4.0L engines is classified as a multi-point, pulse time, speed density fuel delivery system which meters fuel into the intake air stream in accordance with engine demand through 4 or 6 injectors, depending on engine cylinder number, mounted on a tuned intake manifold.

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Fig. Fig. 1: Whenever working on the fuel system, always read the caution, waring or attention labels

An on-board electronic engine control (EEC-IV) computer accepts inputs from various engine sensors to compute the required fuel flow rate necessary to maintain a prescribed air/fuel ratio throughout the entire engine operational range. The computer then outputs a command to the fuel injectors to meter the required quantity of fuel. The EEC-IV engine control system also determines and compensates for the age of the vehicle and its uniqueness. The system will automatically sense and compensate for changes in altitude, such as driving up and down a mountain road.

The fuel injection system uses a high pressure, chassis or tank mounted electric fuel pump to deliver fuel from the tank to the fuel charging manifold assembly. The fuel charging manifold assembly incorporates electrically actuated fuel injectors directly above each of the engine's intake ports. The injectors, when energized, spray a metered quantity of fuel into the intake air stream. A constant pressure drop is maintained across the injector nozzles by a pressure regulator, connected in series with the fuel injectors and positioned downstream from them. Excess fuel supplied by the pump, but not required by the engine, passes through the regulator and returns to the fuel tank through a fuel return line.

On 4-cylinder engines, all injectors are energized simultaneously, once every crankshaft revolution. On 6-cylinder engines, the injectors are energized in two groups of three injectors, with each group activated once every other crankshaft revolution. The period of time that the injectors are energized (injector "on time" or "pulse width") is controlled by the EEC-IV computer. The input from various sensors is used to compute the required fuel flow rate necessary to maintain a prescribed air/fuel ratio.

Fuel supply lines on vehicles with fuel injection will remain pressurized for long periods of time after engine shutdown. This fuel pressure must be relieved before any service procedures are attempted on the fuel system.