Modes of Operation
System Description:
The ECU contains memories for the basic discharge durations of the fuel injectors (determining the air/fuel mixture) at various engine speeds and manifold pressures. The basic discharge duration of the fuel injector is modified by signals from various sensors to obtain the final discharge duration. The oxygen sensor is a main input component for the air/fuel mixture control.
CONTROL FUNCTIONS:
1. Electronic Air Control Valve (EACV):
When the engine is cold, the A/C compressor is ON, the transmission is in gear (automatic transmission), and/or the alternator is charging, the ECU controls current to the electronic air control valve (EACV) to maintain correct idle speed.
2. Ignition Timing Control:
The ECU contains memories for basic ignition timing at various engine speeds, manifold pressures and the coolant temperature.
3. Starting Control:
When the engine is started, the ECU provides a rich mixture.
4. Fuel Pump Control:
When the ignition is initially switched ON, the ECU 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 ECU supplies ground to the main relay which supplies current to the fuel pump.
When the engine is not running and the ignition is turned ON, the ECU cuts the ground to the main relay which cuts the current to the fuel pump.
5. Fuel Cut-Off Control:
During deceleration with the throttle valve closed, current to the injectors is cut-off to improve fuel economy at engine speeds over the following rpm's.
8 valve engine (D15B8):
M/T: 920 rpm
A/T: 900 rpm
16 valve engine (D15B7):
870 rpm
16 valve VTEC-E engine (D15Z1):
850 rpm
Fuel cut-off also takes place when engine speed exceeds the following RPM'S, regardless of throttle valve position, to protect the engine from over-revving.
8 valve engine (D15B8):
6650 rpm
16 valve engine (D15B7):
5800 rpm
16 valve VTEC-E engine (D15Z1):
6300 rpm
NOTE: VTEC-E engine (D15Z1): fuel cut-off also takes place when vehicle speed exceeds, 113 mph (182 km/H).
6. A/C Compressor Clutch Relay:
When the ECU receives a cooling demand signal from the air conditioning system (compressor control unit), it delays the compressor from being energized, and enriches the fuel mixture to assure smooth transition to the A/C mode.
7. EGR Control Solenoid Valve (EGR CSV):
When the EGR is required for control of oxides of nitrogen (NOx) emissions, the ECU supplies ground to the EGR control solenoid valve which supplies regulated vacuum to the EGR valve.
8. Purge Control Solenoid Valve:
When the engine coolant temperature is below 167°F (75°C) (D15Z1): engine only) , Others: 158°F (70°C), the ECU supplies ground to the purge control solenoid valve which cuts vacuum to the purge control valve.
9. Alternator Control:
The system controls the voltage generated by the alternator in accordance with the electric load and drive mode. This reduces the engine load to improve the fuel economy.
ECU BACK-UP FUNCTIONS:
1. Fail Safe Function:
When an abnormality occurs in the signal from a sensor, the ECU 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 ECU 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 the ignition is initially turned on, the ECU supplies ground for the "CHECK ENGINE" warning light for about 2 seconds. When an abnormality occurs in a signal from a sensor, the ECU lights the "CHECK ENGINE" warning light, and stores the failure code in erasable memory.