Prelude L4-1958cc DOHC (1989)
Engine Control Module: Description and Operation
Modes of Operation
Fig. 83 ECU Input/Output
With the use of input sensors, it's own logic circuits to make decisions, and the output devices the ECU controls engine operation for maximum
performance while limiting emissions. Some of the other functions are:
Injector Timing And Duration
The ECU contains memories for the basic discharge durations at various engine speeds and manifold pressures. The basic discharge duration,
after being read out from memory, is further modified by signals sent from various sensors to obtain the final discharge duration.
Electronic Air Control
When the engine is cold, the A/C compressor is on, the transmission is in gear (A/T only), power steering oil pressure is high, or the alternator is
charging, the Electronic Air Control Valve (ECU) controls current to the EACV to maintain correct idle speed.
Ignition Timing Control
The ECU contains memories for basic ignition timing at various engine speeds and manifold pressures. Ignition timing is also adjusted for coolant
temperature.
Other Control Functions
1.
Starting Control
When the engine is started, the ECU provides a rich mixture.
2.
Fuel Pump Control
a. When the ignition switch is initially turned on, The ECU supplies ground to the main relay which supplies current to the fuel pump for about
2 seconds to pressurize the fuel system.
b. When the engine is running the ECU supplies ground to the main relay which supplies current to the fuel pump.
c. When the engine is not running and the ignition is on, the ECU cuts off the ground to the main relay which cuts current to the fuel pump.
3.
Fuel Cut-Off Control
a. During deceleration with the throttle valve closed, current to the injectors is cut-off at speeds over 1,200 rpm, to improve fuel economy.
b. Fuel cut-off action also takes place when engine speed exceeds 7,000 rpm regardless of the position of the throttle valve to protect the engine
from over-running.
4.
A/C Compressor Clutch Relay
When the ECU receives a demand for cooling from the air conditioning system (compressor control unit), it delays the compressor from being
