Computers and Control Systems: Description and Operation

PGM-FI SYSTEM
The PGM-FI system on this model is a sequential multiport fuel injection system.

FUEL INJECTOR TIMING AND DURATION
The ECM/PCM contains memories for the basic discharge durations at various engine speeds and manifold air flow rates. 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 [IDLE AIR CONTROL VALVE (IAC VALVE)]
When the engine is cold, the NC compressor is on, the transmission is in gear, the brake pedal is depressed, the P/S load is high, or the alternator is charging, the ECM/PCM controls current to the IAC Valve to maintain the correct idle speed.

IGNITION TIMING CONTROL
- The ECM/PCM contains memories for basic ignition timing at various engine speeds and manifold air flow rates. Ignition timing is also adjusted for engine coolant temperature.
- A knock control system is also used. When detonation is detected by a knock sensor (KS), the ignition timing is retarded (except-F22A1 engine (S).

OTHER CONTROL FUNCTIONS
1. Starting Control
- When the engine is started, the ECM/PCM provides a rich mixture by increasing fuel injector duration.

2. Fuel Pump Control
- When the ignition switch is initially turned on, the ECM/PCM 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/PCM 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/PCM 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 F22A1 (S): 6,600 rpm, H23A1 (USA: Si/Canada: SR): 6,800 rpm or H22A1 (USA: Si VTEC/Canada: SR-V): 7,700 rpm, regardless of the position of the throttle valve, to protect the engine from over-revving.

4. A/C Compressor Clutch Relay
- When the ECM/PCM receives a demand for cooling from the air conditioning system, it delays the compressor from being energized, and enriches the mixture to assure a smooth transition to the NC mode.

5. Evaporative Emission (EVAP) Purge Control Solenoid Valve
- When the engine coolant temperature is above 167'F (75°C) [H22A1 engine (USA: Si VTEC/Canada: SR-V): 158~F (70°C)], the ECM/PCM controls the EVAP purge control solenoid valve which controls vacuum to the EVAP control canister.

6. Intake Air Bypass (IAB) Control Solenoid Valve
- When the engine speed is below 4,800 rpm [H22A1 engine (USA: Si VTEC/Canada: SR-V): 4,600 rpm], the IAB control solenoid valve is activated by a signal from the ECM/PCM, intake air flows through the long intake path, then high torque is delivered.
- At speeds higher than 4,800 (or 4,600) rpm, the solenoid valve is deactivated by the ECM/PCM, and intake air flows through the short intake path in order to reduce the resistance in airflow.

7. Intake Control Solenoid Valve
- When the engine speed is below 4,000 rpm, the ECM/PCM supplies a ground to the intake control solenoid valve. This opens the solenoid valve sending intake manifold vacuum to the intake control diaphragm.

8. Exhaust Gas Recirculation (EGR) Control Solenoid Valve
- When the EGR is required for control of oxides of nitrogen (NOx) emissions, the ECM/PCM controls the EGR control solenoid valve which supplies regulated vacuum to the 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/PCM FAIL-SAFE/BACK-UP FUNCTIONS
1. Fail-safe Function
- When an abnormality occurs in a signal from a sensor, the ECM/PCM 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/PCM 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/PCM supplies ground for the MIL and stores the DTC in erasable memory.
- When the ignition is initially turned ON, the ECM/PCM 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 HO2S, fuel metering-related, idle control system, ECT sensor, EGR system and EVAP control system self-diagnostic functions.
- When an abnormality occurs, the ECM/PCM stores it in its memory.
- When the same abnormality recurs after the ignition switch is turned OFF and ON again, the ECM/PCM 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.

5. Two (or Three) Driving Cycle Detection Method
- A "Driving Cycle" consists of starting the engine, beginning closed loop operation, and stopping the engine.
- If misfiring that increases emissions or EVAP control system malfunction is detected in two consecutive driving cycles, or TWC deterioration is detected in three consecutive driving cycles, the ECM/PCM turns the MIL on.
- 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.