Computers and Control Systems: Description and Operation

Inputs To Engine Control Module, And Outputs:

The Programed Fuel Injection (PGM-FI) System on this model is a Sequential Multiport Fuel Injection System.

FUEL INJECTOR TIMING AND DURATION
The Engine Control Module (ECM) contains memories for the basic discharge durations at various Engine speeds and Manifold pressures. The basic discharge duration, after being read out from the memory, is further modified by signals sent from various sensors to obtain the final discharge duration.

IDLE AIR CONTROL (IAC) VALVE
When the Engine is cold, the Air Conditioning (A/C) Compressor is on, the Transmission is in gear (Automatic Transmission (A/T) only), the Brake Pedal is depressed, the Power Steering (P/S) load is high, or the Alternator is charging, the ECM controls current to the Idle Air Control (IAC) Valve to maintain the correct idle speed.

IGNITION TIMING CONTROL
The ECM contains memories for basic Ignition timing at various Engine speeds and Manifold pressures. Ignition timing is also adjusted for Engine Coolant temperature.

OTHER CONTROL FUNCTIONS
1. Starting Control.
When the engine is started, the ECM provides a rich mixture by increasing Fuel Injector duration.

2. Fuel Pump Control.
When the Ignition Switch is initially turned on, the ECM supplies ground to the PGM-FI Main Relay that supplies current to the Fuel Pump for two seconds to pressurize the Fuel system.
When the Engine is running, the ECM supplies ground to the PGM-FI Main Relay that supplies current to the Fuel Pump.
When the Engine is not running and the Ignition is on, the ECM cuts ground to the PGM-FI Main Relay which cuts current to the Fuel Pump.

3. Fuel Cut-off Control.
During deceleration with the Throttle Valve closed, current to the Fuel Injectors is cut off to improve fuel economy at speeds over 1,100 rpm.
Fuel cut-off action also takes place when Engine speed exceeds, 6,500 rpm (F22B1 engine), 6,600 rpm (F22B2 engine), regardless of the position of the Throttle Valve, to protect the Engine from over-revving.

4. A/C Compressor Clutch Relay.
When the ECM receives a demand for cooling from the Air Conditioning system, it delays the Compressor from being energized, and enriches the mixture to assure smooth transition to the A/C mode.

5. Evaporative Emission (EVAP) Purge Control Solenoid Valve.
When the Engine Coolant temperature is below 167°F (75°C), the ECM controls the EVAP Purge Control Solenoid Valve which cuts vacuum to the EVAP Purge Control Canister.

6. Intake Air Resonator (IAR) Control Solenoid Valve.
When the Engine rpm is below 2,900 rpm, the IAR Control Solenoid Valve is deactivated by the ECM, and Intake Air does not flow from the IAR. At Engine speeds between 2,900 rpm and 3,700 rpm (mid-range), the Solenoid Valve is activated by a signal from the ECM, and Intake Air flows from the IAR.

7. Fuel Injection Air (FIA) Control Solenoid Valve.
When the Engine speed is between 1,300 rpm and 4,500 rpm, the ECM supplies ground to the FIA Control Solenoid Valve, sending Intake Air to the Fuel Injectors.

8. Exhaust Gas Recirculation (EGR) Control Solenoid Valve.
When the EGR is required for control of Oxides of Nitrogen (NOx) Emissions, the ECM controls the EGR Control Solenoid Valve which supplies regulated vacuum to EGR Valve.

9. Alternator Control.
The system controls the voltage generated at the Alternator in accordance with the electrical load and driving mode, which reduces the Engine load to improve the fuel economy.

ECM FAIL-SAFE / BACK-UP FUNCTIONS
1. Fail-Safe Function.
When an abnormality occurs in a signal from a sensor, the ECM ignores that signal and assumes a pre-programmed value for that sensor that allows the Engine to continue to run.

2. Back-up Function.
When an abnormality occurs in the ECM itself, the Fuel Injectors are controlled by a back-up circuit independent of the system in order to permit minimal driving.

3. Self-Diagnosis Function / Malfunction Indicator Lamp (MIL).
When an abnormality occurs in a signal from a sensor, the ECM supplies ground for the MIL and stores the code in erasable memory. When the Ignition is initially turned on, the ECM supplies ground for the MIL for two seconds to check the MIL bulb condition.

4. Two Trip Detection Method.
To prevent false indications, the Two Trip Detection Method is used for the Heated Oxygen Sensor (HO2S), Fuel metering-related, and EGR System self-diagnostic functions. When an abnormality occurs, the ECM stores it in its memory. When the same abnormality recurs after the Ignition Switch is turned OFF and ON again, the ECM informs the driver by lighting the MIL. However, to ease troubleshooting, this function is cancelled when you short the Service Check Connector. The MIL will then blink immediately when an abnormality occurs.