Fuel Injection
PURPOSE
The Electronic Control Unit (ECU), located in the control unit box, processes signals from various input devices regarding engine operating conditions. This information is evaluated in relation to pre-programmed values to calculate injector frequency (opening duration) for optimum air/fuel mixture, performance, driveability and emissions compliance.
Input devices (the ECU receives):
^ Battery supply signal (voltage).
^ Ignition switch signal.
^ Oxygen sensor (lambda sond) signal.
^ Crankshaft speed (RPM) signal from the ignition control unit.
^ Speedometer signal.
^ Crankshaft position signal from the ignition control unit.
^ Knock signal from the ignition control unit.
^ Coolant temperature signal.
^ Air mass meter signal.
^ Gear selector signal (automatic transmission only).
^ Throttle position signal.
^ A/C switch signal.
^ A/C pressure sensor signal.
Output devices (The ECU controls):
^ System relay ground.
^ Fuel injector ground.
^ Cold start injector ground.
^ Idle air valve.
^ Air mass meter signal to the ignition system control unit (ignition ECU input device).
^ Shift indicator light (manual trans. only).
^ Diagnostic socket fault information.
^ "CHECK ENGINE" light.
START-UP PROGRAM:
The start-up program provides for two injection periods per revolution. Under normal operating conditions the ECU uses only one injection period per firing cycle.
WARM-UP PROGRAM:
This program provides a richer air/fuel mixture until the engine coolant has reached a temperature of 60°C (140°F) or above.
NORMAL DRIVING PROGRAM:
During normal driving, the ECU uses various input devices (mostly the mass air flow sensor signal) to regulate injection frequency.
FULL LOAD AND ACCELERATION PROGRAM:
During full load or acceleration, a richer air/fuel mixture is provided to achieve maximum engine power. This also keeps combustion heat and catalytic converter temperature at an acceptable level.
DECELERATION PROGRAM:
During deceleration, the fuel injectors are turned off (in all gears) if engine speed is above 1,800 RPM. Injection is resumed between 1,400 and 2,000 RPM, depending on engine temperature.
ANTI-KNOCK PROGRAM:
Knock causes high and dangerous combustion temperatures. Therefore the fuel injection system provides a richer air/fuel mixture to counteract temperature and knock if the ignition systems "anti-knock program" has been unsuccessful at reducing the knock. The ignition system will first retard the timing by several degrees to reduce knock, if knock persists, the fuel injection system provides a richer air/fuel mixture to eliminate the knocking problem.
RPM LIMITER PROGRAM:
At excess RPM the fuel injectors are turned off to keep the engine from overrevving.
SELF ADJUSTING FUNCTION:
The ECU adapts to engine condition and environment. It adjusts calculations according to assimilated input. Whenever the vehicle is started or driven, the ECU uses the value it has learned from the previous driving period.
SELF ADJUSTING IDLE SPEED FUNCTION:
In time, normal use, wear and coatings will affect the operation of the throttle valve causing less air to enter the intake system. The ECU adjusts the idle speed to these conditions as well as the current engine load (AC operation, headlights....).
SELF ADJUSTING LAMBDA SOND FUNCTION:
The lambda sond (oxygen sensor) operates in a similar fashion. This self-regulating function keeps the air/fuel mixture at a constant midpoint. Therefore the need to adjust CO content is eliminated and no more possible.
EMERGENCY FUNCTION:
There is a "limp home" mode provided when the signal from the mass air flow sensor ceases. This pre-programmed mode sets the fuel injection frequency (opening duration) so the vehicle can be slowly driven to the repair shop.
SELF DIAGNOSIS FUNCTION:
If the self diagnostic circuit ("on board diagnostics") in the ECU detects a fault in the fuel injection system, it activates the "CHECK ENGINE" light. By extracting fault codes from the diagnostic socket, you can determine what component or components need further testing or replacement (see DIAGNOSIS AND TESTING PROCEDURES). The self diagnosis memory can store up to 13 fault codes.