MFI Engine Control System

MFI Control System Component Location

1 – Mass Air Flow (MAF) sensor "OBD";
2 – Intake Air Temperature (IAT) sensor;
3 – Mass Air Flow (MAF) sensor, except "OBD";
4 – Air-fuel ratio sensor, except "OBD";
5 – Engine Coolant Temperature (ECT) sensor;
6 – Throttle Position (TP) sensor;
7 – Camshaft Position (CMP) sensor;
8 – Crankshaft Position (CKP) sensor;
9 – Heated oxygen sensor (HO2S);
10 – Fuel injectors;
11 – Idle speed control actuator;
12 – Vehicle speed sensor (VSS);
13 – Knock sensor;
14 – Transmission range switch;
15 – Ignition switch;
16 – Engine Control Module (ECM);
17 – Air conditioning relay;
18 – Canister purge solenoid valve;
19 – MFI main relay;
20 – Ignition coils;
21 – Fuel pump;
22 – Acceleration sensor;
23 – Data link connector (DLC).

Fuel control is performed by the Engine Control Module (ECM). The ECM controls ignition timing, determines the amount of fuel supplied to the engine, controls the emission control system and idle speed, as well as the A/C compressor clutch, etc. The ECM changes engine operating modes depending on changing operating conditions based on signals from various switches and sensors.

For example, the ECM controls ignition timing based on signals from sensors that respond to crankshaft speed, engine coolant temperature, throttle position, the currently engaged gear, vehicle speed, etc.
The ECM controls idle speed based on signals from sensors that respond to throttle position, vehicle speed, the currently engaged gear, etc.
Mass Air Flow (MAF) Sensor "OBD"

The mass air flow sensor provides the most direct method of measuring engine load, since it measures the amount of air entering the engine. Air flows into the engine through a sensor with heated and cold wire elements that form part of a bridge circuit. The current passing through the heated wire element keeps its temperature constant at a level higher than the temperature of the intake air. The air mass is determined from the current required to maintain the wire element temperature. The greater the airflow and, consequently, its cooling effect, the greater the value of the signal sent to the ECM.