A Multi-port Fuel Injection (MFI) system is used on some 1992 and all 1993-98 model engines. The MFI system is controlled by a pre-programmed digital computer known as the Engine Control Module (ECM). The ECM controls ignition timing, air/fuel ratio, emission control devices, charging system and idle speed. The ECM constantly varies timing, fuel delivery and idle speed to meet changing engine operating conditions.
Various sensors provide the input necessary for the ECM to correctly regulate the fuel flow at the fuel injectors. These include the manifold absolute pressure, throttle position, oxygen sensor, coolant temperature, intake air temperature, and camshaft and crankshaft position sensors. In addition to the sensors, various switches also provide important information. These include the neutral safety, air conditioning, air conditioning clutch, and brake light switches.
All inputs to the ECM are converted into signals which are used to calculate and adjust the fuel flow at the injectors or ignition timing or both. The ECM accomplishes this by varying the pulse width of the injectors to adjust the fuel/air ratio, or advancing or retarding timing. The ECM tests many of its own input and output circuits. If a fault is found in a major system, this information is stored in the ECM as a Diagnostic Trouble Code (DTC). Information on this fault can be displayed to a technician by means of the grounding a terminal and reading the check engine lamp flashes or by connecting a scan tool and reading the DTCs ( see Driveability & Emission Controls for a more complete procedure).