Modes of Operation
PGM-FI System Description:
The ECM contains memories for the basic discharge durations of the fuel injectors (determining the air/fuel mixture) at various engine speeds and manifold pressures. Basic discharge durations of the fuel injectors is modified by signals from various sensors to obtain final discharge duration. The oxygen sensor is a main input component for air/fuel mixture control.
CONTROL FUNCTIONS:
1. Electronic Air Control:
When engine is cold, A/C compressor is ON, transmission is in gear (automatic transmission), and/or the alternator is charging, the ECM controls current to the Idle Air Control Valve (IAC) to maintain correct idle speed.
2. A/C Compressor Clutch Relay:
When the ECM receives a demand for cooling from the air conditioning system (A/C switch), it delays the compressor from being energized to assure smooth transition to A/C mode.
3. Starting Control:
When the engine is started, the ECM provides a rich mixture.
4. Fuel Pump Control:
When the ignition is initially switched ON, the ECM supplies ground to the main relay which supplies current to the fuel pump for 2 seconds to pressurize the system.
When the engine is running, the ECM supplies ground to the main relay which supplies current to the fuel pump.
When the engine is not running and ignition is turned ON, the ECM cuts ground to main relay which cuts current to the fuel pump.
5. Fuel Cut-Off Control:
During deceleration with throttle valve closed, current to the injectors is cut-off at speeds above the following rpm, to improve fuel economy.
1500 rpm
Fuel cut-off action also takes place when engine speed exceeds the following rpm, regardless of throttle position to protect the engine from over-running.
6600 rpm
6. A/C Compressor Clutch Relay:
When the air conditioner (A/C switch) is turned ON, it delays compressor from being energized to assure smooth transition to the A/C mode.
7. EGR Control Solenoid Valve (EGR CSV):
When EGR is required for control of oxides of nitrogen (NOx) emissions, the ECM supplies ground to the EGR control solenoid valve which supplies regulated vacuum to the EGR valve.
8. Purge Cut-Off Control Solenoid Valve:
When engine coolant temperature is below 75°C / 167°F, the ECM supplies a ground to the purge cut-off solenoid valve which cuts vacuum to the purge control valve.
9. Intake Air Control Solenoid Valve (USA: EX, SE / Canada: EX-R, SE):
When engine speed is below 3500 rpm, the ECM supplies a ground to the intake control solenoid valve. This opens the solenoid valve sending intake manifold vacuum to intake control diaphragm.
10. Alternator Control:
The system controls the voltage generated by the alternator in accordance with electrical load and drive mode. This reduces engine load to improve fuel economy.
11. Intake Air Bypass (IAB) Control Solenoid Valve (USA: EX, SE / Canada: EX-R, SE)
When engine RPM is below 5000, the IAB is activated by a signal from the ECM. This lets intake air flow through the long intake path to add more engine torque. When the engine RPM is above 5000, the solenoid valve is deactivated by the ECM. This lets intake air flow through the short intake runners to reduce airflow resistance.
ECM BACK-UP FUNCTIONS:
1. Fail Safe Function:
When an abnormality occurs in the signal from a sensor, the ECM ignores that signal and assumes a pre-programmed value that allows the engine to continue to run.
2. Back-Up Function:
When an abnormality occurs in the ECM itself, the injectors are controlled by a back-up circuit independent of the system in order to permit normal driving.
3. Self-Diagnosis Function:
When an abnormality occurs in a signal from a sensor, the ECM lights the "MALFUNCTION INDICATOR LAMP", and stores the failure code in erasable memory. When the ignition is initially turned on, the ECM supplies ground for the "MALFUNCTION INDICATOR LAMP" for about 2 seconds to check bulb condition.