Fuel Injection System - 4.0L MPFI: Description

The Multi-Point Fuel Injection (MPFI) system used on the 4.0L engine is electronically controlled by an Electronic Control Unit (ECU). The ECU monitors and analyzes inputs from various sensors, computes engine fuel and ignition timing requirements based on these inputs, then meters fuel delivery to each fuel injector. There are 2 different modes of operation, "Open Loop" and "Closed Loop".

During "Open Loop" modes, the ECU receives input signals and responds only according to the programming that was preset into the ECU. Input from the oxygen (O2) sensor is not monitored during "Open Loop".

During "Closed Loop" modes, the ECU does monitor the oxygen sensor (O2) input. The oxygen sensor input indicates to the ECU whether or not the calculated injector pulse width results in the ideal air/fuel ratio of 14.7 parts air to 1 part fuel. The ECU can "Fine-Tune" the injector pulse width to achieve this optimum fuel economy combined with low emission engine performance.